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The Effect of Castration Timing and Preconditioning Program on Beef Calf Performance

Permanent Link: http://ufdc.ufl.edu/UFE0043824/00001

Material Information

Title: The Effect of Castration Timing and Preconditioning Program on Beef Calf Performance
Physical Description: 1 online resource (148 p.)
Language: english
Creator: Taylor, Amie M
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: additive -- beef -- calf -- castration -- preconditioning -- timing
Animal Sciences -- Dissertations, Academic -- UF
Genre: Animal Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: This study had two objectives. First, to determine if timing of castration in nursing calves affected calf performance, primarily weaning weight. Ninety-two calves were assigned to one of two castration treatments, early (average age at castration 36 days) or late (average age at castration 131 days). Calves were stratified to treatment by birth date, breed (Angus or Brangus), and cow age. All calves were surgically castrated using the Newberry Knife to incise the scrotum and traction to remove the testes. Birth weight was similar between early and late castrates at the onset of the experiment. Actual weaning weight, adjusted 205-d weaning weight, and body weight change throughout the experimental period were all similar between early and late castrate treatments. This study suggests that delaying castration until calves were more advanced in age was not advantageous to increasing weaning weight. The second objective was to evaluate the response of weaned calves to different feed additives within a preconditioning supplement. Specifically, alternatives to antibiotics and ionophores were evaluated to determine their effectiveness in improving calf performance and mitigating the stress response observed during the weaning process. Following stratification by bodyweight, sex, previous castration status, and breed, 160 calves were randomly allotted to one of four treatments (n=40 calves/treatment): 1) control calves (CON) were supplemented without additives; 2) Chlortetracycline calves (CTC) were supplemented with added chlortetracycline at 350 g/hd/d; 3) Monensin calves (RUM) were supplemented with added Rumensin at 175 mg/hd/d; and 4) Actigen® calves (ACT) were supplemented with added Actigen® at 10 g/hd/d. Calf bodyweight was similar among treatments at the beginning of the trial period. Over the 52-day preconditioning period, ACT resulted in the greatest gain response. Chlortetracycline calves exhibited similar gains to ACT, which were both greater than gains exhibited by RUM. Control calves were similar to both medicated treatments, but did not gain as much as ACT. Plasma concentrations of haptoglobin and ceruloplasmin were similar among treatments; however, a day effect was observed in both acute phase proteins measured. Our results indicate Actigen® may improve calf performance as effectively as chlortetracycline during a preconditioning period of this length, but neither additive was effective at mediating stress post-weaning.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Amie M Taylor.
Thesis: Thesis (M.S.)--University of Florida, 2011.
Local: Adviser: Thrift, Todd A.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0043824:00001

Permanent Link: http://ufdc.ufl.edu/UFE0043824/00001

Material Information

Title: The Effect of Castration Timing and Preconditioning Program on Beef Calf Performance
Physical Description: 1 online resource (148 p.)
Language: english
Creator: Taylor, Amie M
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: additive -- beef -- calf -- castration -- preconditioning -- timing
Animal Sciences -- Dissertations, Academic -- UF
Genre: Animal Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: This study had two objectives. First, to determine if timing of castration in nursing calves affected calf performance, primarily weaning weight. Ninety-two calves were assigned to one of two castration treatments, early (average age at castration 36 days) or late (average age at castration 131 days). Calves were stratified to treatment by birth date, breed (Angus or Brangus), and cow age. All calves were surgically castrated using the Newberry Knife to incise the scrotum and traction to remove the testes. Birth weight was similar between early and late castrates at the onset of the experiment. Actual weaning weight, adjusted 205-d weaning weight, and body weight change throughout the experimental period were all similar between early and late castrate treatments. This study suggests that delaying castration until calves were more advanced in age was not advantageous to increasing weaning weight. The second objective was to evaluate the response of weaned calves to different feed additives within a preconditioning supplement. Specifically, alternatives to antibiotics and ionophores were evaluated to determine their effectiveness in improving calf performance and mitigating the stress response observed during the weaning process. Following stratification by bodyweight, sex, previous castration status, and breed, 160 calves were randomly allotted to one of four treatments (n=40 calves/treatment): 1) control calves (CON) were supplemented without additives; 2) Chlortetracycline calves (CTC) were supplemented with added chlortetracycline at 350 g/hd/d; 3) Monensin calves (RUM) were supplemented with added Rumensin at 175 mg/hd/d; and 4) Actigen® calves (ACT) were supplemented with added Actigen® at 10 g/hd/d. Calf bodyweight was similar among treatments at the beginning of the trial period. Over the 52-day preconditioning period, ACT resulted in the greatest gain response. Chlortetracycline calves exhibited similar gains to ACT, which were both greater than gains exhibited by RUM. Control calves were similar to both medicated treatments, but did not gain as much as ACT. Plasma concentrations of haptoglobin and ceruloplasmin were similar among treatments; however, a day effect was observed in both acute phase proteins measured. Our results indicate Actigen® may improve calf performance as effectively as chlortetracycline during a preconditioning period of this length, but neither additive was effective at mediating stress post-weaning.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Amie M Taylor.
Thesis: Thesis (M.S.)--University of Florida, 2011.
Local: Adviser: Thrift, Todd A.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0043824:00001


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1 THE EFFECT OF CASTRATION TIMING AND PRECONDITIONING PROGRAM ON BEEF CALF PERFORMANCE By AMIE MARIE T AYLOR A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DE GREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2011

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2 2011 Amie Marie T aylor

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3 To Brandon, for being my best friend and teaching me how to gig a frog.

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4 ACKNOWLEDGMENTS I would like to thank Dr. Todd Thrift for providing me with the o pportunity to continue my education. These additional years of guidance and support as I pursued my graduate degree were filled with more than just lessons about the beef cattle industry, but also lessons on how to balance a career with the important thing s in life like family and friends. Dr. Thrift supported my passion for teaching wholeheartedly while I was in graduate school, offering me encouragement and opportunities inside and outside of the classroom along the way. He has both challenged and enabled me to become a better educator and I have never been more confident in my abilities to teach. For this, I will forever be grateful. I would also like to thank my committee co chair, Dr. Matt Hersom. Dr. Hersom broadened my experience as a graduate studen t with research opportunities that took me outside of my comfort zone and challenged me to better understand the science behind beef cattle management. In addition, I would like to thank my final committee member, Dr. Brian Myers, for his continued support and training as a teacher educator. Dr. Myers has been instrumental in offering technical support and encouragement for my curriculum project on Beef Quality Assurance. Additionally, I would like to sincerely thank my family and friends for their contin ued support over the years. Specifically I want to thank my parents for their enduring love and persistent encouragement to never settle for less than what I deserve. My grandparents for challenging me to pursue a graduate degree, and their willingness to read my thesis and offer suggestions throughout my graduate experience My brother for his leadership and his willingness to selfless ly serve our country Josh has been a role model for me and has always set the bar high, challenging me to

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5 exceed expectat ions while blazing my own path. My frien ds both within and outside the D epartment of Animal Science s I have many memories that I will cherish fondly and certainly were sources of encouragement throughout my graduate experience. I would be remiss not t o thank my husband for his love and support over the past 11 years Brandon has always been willing to patiently teach me skills that I know will come in handy when I begin my career as an agricultural educator. More importantly, for his understanding these past few months and for never complaining when I pulled out a frozen pizza more than once a week as I prepared for my defense! Lastly, I would like to thank God for blessing me and providing me with the opportunities to pursue my goals. I have been blessed beyond words with a family who has instilled in me a passion for agriculture, and the skill set to pursue a career in the industry that sustains us.

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ .......... 9 LIST OF ABBREVIATIONS ................................ ................................ ........................... 10 ABSTRACT ................................ ................................ ................................ ................... 11 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 13 2 REVIEW OF LITERATURE ................................ ................................ .................... 15 Castration ................................ ................................ ................................ ............... 15 Purpose ................................ ................................ ................................ ............ 15 Method and Timing of Castration ................................ ................................ ..... 19 Surgical methods ................................ ................................ ....................... 19 Non surgical methods ................................ ................................ ................ 21 Timing of castration ................................ ................................ .................... 23 Preconditioning ................................ ................................ ................................ ....... 29 Purpose ................................ ................................ ................................ ............ 29 Effect of preconditioning on calf health ................................ ...................... 32 Effect of preconditioning on calf performance ................................ ............ 36 Effect of preconditioning on carcass attributes ................................ ........... 40 Effect of preconditioning on calf stress ................................ ...................... 44 Effect of preconditioning on calf value ................................ ....................... 54 Factors Influencing Precon ditioning Economics and Profitability ...................... 60 Preconditioning system ................................ ................................ .............. 62 Preconditioning time period ................................ ................................ ........ 66 Nutritional supplementation and rate of gain ................................ .............. 69 3 EFFECT OF TIMING OF CASTRATION ON NURSING CALF BODYWEIGHT GAIN AND WEANING WEIGHT ................................ ................................ ............. 92 Story in Brief ................................ ................................ ................................ ........... 92 Rationale ................................ ................................ ................................ ................. 92 Materials and Methods ................................ ................................ ............................ 94 Results and Discussion ................................ ................................ ........................... 95 4 THE COMPARISON OF FEED ADDITIVES DURING PRECONDITIONING ON GROWTH AND PERFORMANCE OF BEEF CALVES ................................ ......... 101

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7 Story in Brief ................................ ................................ ................................ ......... 101 Rationale ................................ ................................ ................................ ............... 102 Materials and Methods ................................ ................................ .......................... 103 Animals and Treatments ................................ ................................ ................. 104 Feed Sampling ................................ ................................ ............................... 105 Sampling and Analysis ................................ ................................ ................... 106 Results and Discussion ................................ ................................ ......................... 107 Animal Performance ................................ ................................ ....................... 107 Animal Stress ................................ ................................ ................................ 114 Economic Evaluation ................................ ................................ ...................... 116 5 CONCLUSIONS ................................ ................................ ................................ ... 131 LIST OF REFERENCES ................................ ................................ ............................. 132 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 148

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8 LIST OF TABLES Table page 3 1 The effect of age at castration on calf growth perfor mance ................................ 99 4 1 Nutritive value of preconditioning supplement, pasture, and peanut hay (PHAY) offered to calves throughout the experiment. ................................ ...... 119 4 2 The effect of supplemental feed additive treatment on calf growth during preconditioning ................................ ................................ ................................ 120 4 3 An economic evaluation of supplemental feed additive treatment during precondit ioning ................................ ................................ ................................ 121

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9 LIST OF FIGURES Figure page 3 1 Effect of castration timing on calf bodyweight in May. P=0.98. ......................... 100 4 1 Effect of feed additive treatment on bodyweight change during a 52 day preconditioning program. P=0.01. ................................ ................................ .... 122 4 2 Effect of feed additive treatment on average dail y gain during a 52 day preconditioning period. P=0.002. ................................ ................................ ...... 123 4 3 Effect of feed additive treatment on bodyweight change during a 7 day drylot period of a preconditioning period. P=0.02. ................................ ...................... 124 4 4 Effect of feed additive treatment on 14 day average daily gain during a 52 day preconditioning period. P=0.01. ................................ ................................ 125 4 5 Effect o f feed additive treatment on average daily gain from day 14 through day 52 of a preconditioning program. P=0.06. ................................ .................. 126 4 6 Effect of feed additive treatment on average daily gain during the past ure period of a preconditioning program. P=0.02. ................................ ................... 1 27 4 7 Effect of sampling day on plasma concentration of haptoglobin post weaning. P<0.0001. ................................ ................................ ................................ ......... 128 4 8 Effect of sampling day on plasma concentration of ceruloplasmin post weaning. P<0.0001. ................................ ................................ .......................... 129 4 9 Effect of feed additive treatment and sampling day on plasma concentratio n of ceruloplasmin post weaning. P=0.01. ................................ ........................... 130

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10 LIST OF ABBREVIATION S ACTH Adrenocorticotropic Hormone ADG Average Daily Gain APP Acute Phase Protein APR Acute Phase Response BRD Bovine Respiratory Disease BW Bodyweight BWC Bodyweight Change CP Crude Protein HPA Hypothalamic Pituitary Adrenal NAHMS National Animal Health Monitoring System TDN Total Digestible Protein UIP Undegradable Intake Protein USDA United States Department of Agriculture

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11 Abstract of Thesis Presente d to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science THE EFFECT OF CASTRATION TIMING AND PRECONDITIONING PROGRAM ON BEEF CALF PERFORMANCE By Amie Marie T aylor December 2011 Chair: Todd Thrift Major: Animal Science s This study had two objective s First, to determine if timing of castration in nursing calves affected calf performance, primarily weaning weight. Ninety two calves were assigned to one of two castr ation treatments, early (average age at castration 36 days) or late (average age at castration 131 days). Calves were stratified to treatment by birth date, breed (Angus or Brangus), and cow age. All calves were surgically castrated using the Newberry Knif e to incise the scrotum and traction to remove the testes. Birth weight was similar between early and late castrates at the onset of the experiment. Actual weaning weight, adjusted 205 d weaning weight, and body weight change throughout the experimental pe riod were all similar between early and late castrate treatments. This study suggests that delaying castration until calves were more advanced in age was not advantageous to increasing weaning weight. The second objective was to evaluate the response of weaned calves to different feed additives within a preconditioning supplement. Specifically, alternatives to antibiotics and ionophores were evaluated to determine their effectiveness in improving calf performance and mitigating the stress response observe d during the weaning process. Following stratification by bodyweight, sex, previous castration status, and

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12 breed, 160 calves were randomly allotted to one of four treatments (n=40 calves/treatment): 1) control calves (CON) were supplemented without additiv es; 2) Chlortetracycline calves (CTC) were supplemented with added chlortetracycline at 350 g/hd/d; 3) Monensin calves (RUM) were supplemented with added Rumensin at 175 mg/hd/d; and 4) Actigen calves (ACT) were supplemented with added Actigen at 10 g/hd /d. Calf bodyweight was similar among treatments at the beginning of the trial period. Over the 52 day preconditioning period, ACT resulted in the greatest gain response. Chlortetracycline calves exhibited similar gains to ACT, which were both greater than gains exhibited by RUM. Control calves were similar to both medicated treatments, but did not gain as much as ACT. Plasma concentrations of haptoglobin and ceruloplasmin were similar among treatments; however, a day effect was observed in both acute phase proteins measured. Our results indicate Actigen may improve calf performance as effectively as chlortetracycline during a preconditioning period of this length, but neither additive was effective at mediating stress post weaning.

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13 CHAPTER 1 INTRODUCTION There are a variety of production practices cow calf producers can implement to beef calves either before weaning, at weaning, or post weaning. Common practices include castration, identification, health management, dehorning, growth implant administratio n and preconditioning. Due to the diversity and geographic range of the United States cow calf industry, implementation of these on farm practices can vary widely Such differences in management not only impact the supply of calves available for beef produ ction, but the quality and subsequent performance of calves in the stocker, feedlot, and harvesting segments (Avent, 2002 ) Consequently cow calf producers can significantly impact the value of their calves through on farm management (Schulz et al., 2010 ) C urrent literature illustrate s a clear need to implement some of these management practices such as castration and dehorning However, the manner and timing at which they should be implemented is less obvious. The first objective of this study was to de termine if diff erences in age at castration resulted in significant differences in growth during the nursing phase and at weaning. Since castration is a common practice within the United States beef industry it would be beneficial to producers if a standar d time frame for castration and other calf management practices could be established. Preconditioning, the process of weaning and preparing calves for a future phase of production (Savell, 2008), is another management practice implemented by cow calf prod ucers. Although the practice of preconditioning was designed to improve calf performance and health post weaning (Lalman and Smith, 2002 ), literature and economic analyses available on preconditioning report variable and often conflicting

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14 results. This lea ves many producers hesitant to adopt preconditioning as an annual practice and assume the risk associated with holding calves for a period of time beyond weaning. At the same time there is a growing demand for preconditioned calves in the stocker and fee dlot segments e specially as the market for naturally raised and organic beef expands and the use of antibiotics in food animal production is scrutinized by consumers This phenomenon has forced producers to re evaluate the need for preconditioning their c alves either on their ranch of origin or through a custom preconditioning yard. T he second objective of this study was to evaluate the response of weaned calves to different supplemental feed additives during preconditioning. Specifically, alternatives to feed technologies like antibiotics and ionop hores were evaluated Additives identified to i mprove calf performance during the preconditioning phase over that of supplement or grazing alone could increase flexibility in marketing and help producers economi cally justify the cost and risks associated with preconditioning

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15 CHAPTER 2 REVIEW OF LITERATURE Castration Purpose Castration the removal or destruction of the testicles, is a common management practice within beef cattle operations of the United States. Approximately 60% of cow calf producers castrat ed their male calves prior to sale ( USDA NAHMS, 2007) There are several reasons producers would choose to castrate before marketing calves with the primary reason being driven by market demand and economics C astrated calves are generally valued higher in the market place compared to their non castrated male co ntemporaries. Troxel et al. reported that steers in Arkansas sale barns consistently sold at a premium compared to bulls in the feeder calf market (T roxel and Barham, 2007; Troxel et al 2002). S teers received a premium of $4.63 + 0.08/45.45 kg and $6.48 + 0.09/45.45 kg over the average selling price of all calves sold through Arkansas markets in 2000 and 2005 respectively (Troxel and Barham, 2007). This trend can also be observed in feeder calf markets throughout the United States, not just in Southeastern sale barns. In a similar study condu cted by Smith et al. ( 2000 ) bulls sold in 1997 and 1999 at Oklahoma auction barns were discounted relative to steers. In 2009, model estimated prices for feeder calves marketed through sale barns in Kansas and Missouri showed that at weights of 250 kg bulls received discounts of up to $5.91/ 45.45 kg compared to similar weigh t steers (Schulz et al., 2009). These r esult s indicate produce rs could lose approximately $20 per head to $30 per head, depending upon market conditions, if they fail to castrate male calves prior to sale.

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16 The premiums associated with castrated males over that of their intact counterparts are d ue in part to the current structure of the United States fed beef cattle industry. The vast majority of beef produced in the United States is so urced from cattle fed in confined feedlot operations with greater than 1,000 head capacity ( USDA NAHMS, 1999) I ntact males express more aggressive and sexual behaviors than castrated males, which can lead to decreases in meat quality and an increased incidence of injury to both handlers and animals (Coetzee et al., 2010) As a result, feedlot operators demand that male calves being placed on feed be castrate d. Although feedlots castrate male calves, feeders prefer to purchase steers over bulls due to performance reductions and risks associated with castrating heavy weight, post pubertal calves ( Bretschneider 2005 ; K night et al., 2000 ; Worrell et al., 1987 Addis et al. (197 3 ) Zweiacher et al. (1979), and Berry et al. (2001) each performed a series of experiments comparing calves castrated prior to and at place ment in a feedlot Each investigator reported that calve s purchased as steers exhibited greater (P<0.05) gains over the trial periods than calves castrated upon arrival. Addis et al. (1973) reported purchased steers had a 9.4% greater overall gain than bulls castrated on arrival during an 82 day test period. Ca strates gained 0.80 kg more than bulls castrated by banding and 1.00 kg more than bulls castrated by the emasculator on arrival (Zweiacher et al., 1979). Berry et al. (2001) also showed bulls banded on arrival at the feedlot exhibited a 19% decrease in ave rage daily gain compared to purchased steers. In addition, purchased steers had increased (P<0.03) dry matter intakes and reduced (P<0.05) morbidity compared to surgical and non surgical castrates (Berry et al., 2001 ; Zweiacher et al., 1979 )

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17 Similar find ings were reported i n a large scale study evaluating weight gain and health of bull calves castra ted upon arrival at a stocker facility (Ratcliff et al., 2005). Bulls castrated on arrival gained 0.12 kg per head per day less (P<0.01) during th e receiving p eriod than purchased steers Although castrated bulls had similar gains to steer s during the extended stocker phase, steers exhibited higher average daily gains over the entire trial period due to lost performance by bulls during the receiving period. In a ddition, bull s castrated on arrival had an 8% higher (P=0.08) morbidity rate compared to calves purchased as steers. Aside from aggressive behavior exhibited by intact males and lost performance seen in late castrates consumer preferences largely drive t he need for castrated beef calves within the United States I ntact males are superior to their castrated contemporaries in their ability to efficiently grow and deposit lean muscle tissue (Bailey et al., 1966; Champagne et al., 1969; Klosterman et al., 195 4 ). Unfortunately, bulls lack the ability to produce an acceptable carcass for the American consumer (Field, 1971; Forrest, 1975; Reagan et al., 1971; Seideman et al., 1982 ). Bull carcasses consistently produce lower quality grade carcasses than those pro duced by s teers Champagne et al. (1969) determined that bull carcasses displayed significantly less marbling (P<0.01) and subsequent ly had lower carcass quality g rades than steers in a group of Hereford male calves. These results agree with other finding s reported by Gortsema et al. (1974) Jacobs et al. (1977), and Landon et al. (1978) where crossbred steers of both English and Continental breed types produced higher quality grade carcasses than bulls of the same breed type and weight.

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18 Additional ly, bul l carcasses tend to produce tougher and darker beef than beef produced by steer s (Seideman et al., 1982) Field (1971) reviewed seven studies that evaluated tenderness in bull and steer carcasses. All seven studies concluded that meat from bulls had higher Warner Bratzler shear force values than meat from steers, indicating bull meat is tougher Hunsley (1971) determined that differences in shear force values between bulls and steers widen as age at harvest increases Differences in carcass characteristics are substantiated by studies that compare bull meat to steer meat in taste panels and consumer acceptance surveys. In a study conducted by Jacobs et al. (1977), researchers found tha t 60% of consumer respondents in a blind survey from three retail outlets preferred the overall palatability of beef from steer s to beef from bul ls O ver 45 % of these same consumers respond ed that cuts purchased and prepared from the round of bulls were inferior to previous purchases of beef. In a trained sensory panel test cond ucted by Reagan et al. (1971), panelists found significant differences in flavor, tenderness, and overall acceptability in two different comparisons of steak s from steers and bulls. Forrest (1975) reported that a trained taste panel ranked rib roasts harve sted from steers as more (P<0.05) desirable than those harvested from bulls in tenderness, juiciness, flavor, and overall palatability. It has also been suggested that quality grade and palatability differences exist between steers castrated prior to wean ing an d those castrated after weaning and closer to puberty. Prigge (1976 ) reported that calves cas trated at weights exceeding 250 kg produced carcasses similar to that of bulls in fat composition and quality. Heaton et al. (2006) reported differences in t enderness, juiciness, flavor, and overall palatability with a consumer panel that ate beef on a regular basis These consumer panelists ranked

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19 steaks from steers castrated before 90 days of age higher (P<0.04) in all of the above palatability attributes th an steaks from steers castrated after 225 days of age There are clear disadvantages to utilizing intact males within the United States beef industry. Aggressive behavior, reduced carcass quality, and poor consumer acceptance of bull meat all drive market demand for castrated calves. Additionally, lost performance associated with the added stress of castrating heavy weight, post pubertal calves in the stocker and feedlot segments illustrate a need for cow calf producers to implement the practice before mar keting calves at weaning Method and Timing of Castration According to Lents et al. (2006), over 17 mill ion calves under the age of one year are castrated annually in the United States. USDA NAHMS data from 2007 would support this, reporting that the majo rity of these calves are castrated prior to sale on their ranch of origin Although it seems castration is a common practice the method and age at which calves are castra ted is highly variable. Reports suggest age at castration can range from 1 day of age to over 123 days of age, with nearly 20% of cow calf producers opting to castrate after 123 days of age ( USDA NAHMS, 2007) A pproximately half of the cow calf producers use d surgical methods to castrate calves, while the remaining half utilize d non surgic al methods ( USDA NAHMS, 2007). Factors ranging from producer philosophy, perceived cal f stress, operational resources and size may determine th e methodology and timing at which castration is implemented. Surgical m ethods Surgical castration encompass es a v ariety of techniques that ultimately incise the scrotum to expose the testicles, after which the testicle s are removed Scrotal incisions can be made with either a knife blade or a scalpel, and should be placed high enough

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20 on the scrotum to allow for prope r drainage. Correct incision placement can help prevent fluid build up and subsequent infection during the healing process. When using a knife blade or scalpel, adequate drainage can be achieved by pushing the testicles into the upper portion of the scrotu m or body cavity before removing the bottom half of t he scrotum When castrating with the Newberry Knife, the same procedure should be followed before incising the sides of the scrotum. This ensures the anterior and posterior flaps created by the incision properly expose the testicles and allow for drainage. Once the scrotum has been incised, the spermatic cord must be severed completely to remove the testicles Severing the spermatic cord can be accomplished through the use of traction, scraping with a bl ade, crushing, or twisting the spermatic cords. Traction is performed by holding the exposed testicles and using downward force to pull the testicles until the spermatic cord breaks. Scraping the spermatic cord facilitates the separation of tissues and ves sels during the removal process. The emasculator tool can be used to remove the cord while crushing or crimping associated blood vessels, which may reduce hemorrhaging in larger, more sexually mature cattle (Lane et al. 2010) Twisting is performed when u sing the Henderson Castration T ool TM which can also effectively severe the spermatic cord and reduce significant blood loss in older bulls (Jensen, 2006) Surgical castration is highly effective. Following the procedure, producers can be assured both test icles were removed unlike some non surgical methods However, surgical castration can be stressful and result in post castration hemorrhage and i nfection if not executed properly ( Coetzee et al., 2010 ) This risk may increase when

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21 surgical castration is pe rformed in heavy weight, post pubertal males ( Coetzee et al., 2010 ; Lane et al., 2010) Non s urgical m ethods Non surgical castration is generally referred to as bloodless castration since these methods destroy and/or remove the testicles without subsequen t blood loss and hemorrhaging. There are two primary non surgical methods banding and the emasculatome. Banding, by either the elastrator, Callicrate Bander TM or similar device, applies an elastic band around the scrotum, above the testes. These bands impede blood flow through the spermatic cord eventually creating a necrotic state that causes the testicles and scrotum to slough off within a period of weeks. The elastrator is only recommended for use in calves less than one month of age (Lane et al. 2010). The Callicrate Bander TM works in a similar fashion to the elastrator except that it employs a much larger elastic band, which is tightened by a ratchet mechanism and secured with a metal grommet. This tool can be used in older, heavier weight c attle (Jenson, 2006). O perators should exercise caution when applying the bands with either method. Failed castration and complications can result if the elastic band is misplaced or not tightened correctly. The risk of prolonged wound formation at the si te of band placement seems to increase as age at castration increases (Fisher et al., 2001; Knight et al., 2000). Additionally, all calves should be vaccinated with a tetnus antitoxin to avoid anaerobic infection that may result from the procedure. The Bu rdizzo emasculatome is another bloodless method used by some cattleman. The emasculatome works by crushing the spermatic cords and prohibiting blood flow to the testicle. The loss of blood flow and reduction of nervous function

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22 allows the testicles to atro phy and become non functional. Prior to the screwworm eradication, the use of e masculatomes by cow calf producers w as common since the procedure did not require incising the scrotum and creating a wound that would attract the insect (Capucille et al., 2002 ) Today, emasculatomes are used by only 3.5 percent of cow calf operations in the United States ( USDA NAHMS, 2007). Many producers perceive non surgical methods as less stressful a nd labor intensive than surgical methods Although some data may support th is philosophy ( Fisher et al., 1996 ; King et al., 1991; Robertson et al., 1994 ), other reports suggest that there is minimal difference if any in the stress response associated with non surgical techniques ( Berry et al., 2001; Fisher et al., 2001 ; Warnock 2010 ) Warnock (2010) evaluated castration method on calf performance and stress response in a feedlot setting. Male calves were assigned to one of five treatments; control calves surgically castrated prior to weaning at an average age of 52 days, intact bulls, bulls castrated by a Callicrate Bander TM upon arrival (d 0) bu lls castrated by the Henderson C astrati on T ool TM upon arrival (d 0) and bulls castrated surgically upon arrival (d 0) During the first two weeks of the arrival period, control calves gained 0.7 kg per head per day, while bulls castrated surgically, with the Henderson C astration T ool TM and with the Callicrate Bander TM gained 0.2, 0.2, and 0.1 kg per head per day, respectively. Since stress has the abilit y to reduce performance these r esults indicate short term stress elicited by castration will occur regardless of method used. Although differences were initially observed during the two week arrival period, gain response for the entire 84 day trial period was similar among all treatment groups, indicating c alves recovered from late castration, regardless of method used

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23 Warnock (2010) also evaluated the acute phase response to castration method. Acute phase proteins, like ceruloplasmin and haptoglobin, have been utilized to quantify the stress response associated with a particular management practice over that of performance alone (Arthington et al., 2003) Intact bulls and bulls castrated either surgic ally, by the Henderson Castration T ool TM or by the Callicrate Bander TM exhibited simi lar ceruloplasmin concentrations post castration, which were all higher (P<0.10) than ceruloplasmin levels exhibited by control steers during this measurement period Similarly, haptoglobin levels among the castration methods were similar following castrat ion but numerically higher than control steers. Acute phase responses between castration methods differed between days (P=0.02). Banded bulls exhibited a delayed stress response compared to the stress response exhibited by surgically castrated bulls. Pla sma ceruloplasmin concentrations in banded calves were elevated over that of controls (P<0.10) beginning on day 15. Henderson castrates exhibited elevated (P<0.05) ceruloplasmin concentrations beginning on day 2, but the stress response was mediated by day 15 since ceruloplasmin concentrations between Henderson castrat es and controls were similar after this time Differences in performance and inflammatory response between castrates and control steers post castration indicate all meth ods of castration are s tressful. However, t he amount and duration of stress elicited by specific methods of castration are less clear, and may be dependent on the time at which castration is implemented. Timing of c astration Industry recommendations generally advocate for castr ation to occur as close to birth as possible ( Bretschneider, 2005 ) The general belief is that castration in young,

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24 sexually immature calves elicits less of a stress response and reduces the risk of castration associated blood loss and infection ( King et a l., 1991; Lyons Johnson, 1998; Stafford and Mellor, 2005 ) At the same time, many producers are concerned that castrating too early will reduce growth rates in male calves from birth to weaning (Lehmkuhler, 2003 ) Some evidence exists that bulls gain sligh tly faster than castrates during the nursing phase ( Klosterman et al., 1954 ; Marlowe and Gaines, 1958 ). However, o ther researchers purpose those differences are due primarily to selection (Brinks et al., 1961 ; Cundiff et al., 1966; Koch and Clark, 1955 ) This belief was supported when Tanner et al. (1970) castrated a random sample of male calves born over a three year perio d and found that intact calves did not have a significant weight advantage at weaning to steers. Bulls gained only 0.01, 0.06, and 0.0 kg/d more (P>0.05) than steers pre weaning during the first, second, and third year s of the trial, respectively. These gains resulted in a 3.0 kg advantage (P>0.05) in 205 day weaning weight for bulls compared to steers over the three year period. Similarl y, Brinks et al. (1961) and Flower et al. (1963) reported bulls only exhibited a 1.5 and 2.3 kg heavier (P>0.05) 205 day weaning weight than steers randomly selected for castration respectively. Most literature suggests that castrating close to birth has minimal to no effect on ultimate weaning weight Bailey et al. (1966) compared the pre weaning growth rate of steers surgically castrated at approximately 3 months of age to calves left intact in two separate studies. Differences in pre weaning growth rat e and weaning weight were not significant among the two treatment groups in either study. Data were pooled for both studies since calves were treated in a similar fashion during the pre weaning period of

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25 both experiments. Upon weaning at approximately seve n months of age, bulls on average, weighed 183.5 kg while steers on average, weighed approximately 181.5 kg. These results agree with those of Glimp et al. (1971), King et al. ( 1991 ) and Looper et al. (2005). Glimp et al. (1971) assigned Hereford and A ngus calves to a variety of treatments, including castration at birth or weaning, short scrotum castration at birth or weaning, or left intact. Average daily gain during the pre weaning period and adjusted weaning weight were not different among any of the treatment s Calves castrated at birth by either a rubber band or short scrotum method gained 0.73 and 0.78 kg/day, respectively. Calves remaining i ntact after weaning and calves castrated at weaning either surgically or by the short scrotum method gained 0.73, 0.72, and 0.75 kg/day, respectively. Looper et al. (2005) also reported that steers surgically castrated at birth or at weaning had similar adjusted 205 day weaning weights. Calves castrated at weaning exhibited a 7 kg heavier (P>0.10) adjusted 205 d ay weaning weight than calves castrated at birth. In contrast, Micol et al. (2009) reported that steers castrated at 10 months of age had greater live weight gains from birth to weaning than steers castrated at 2 months of age (1.06 vs. 1.01 kg/day) Howev er, steers castrated at 2 months of age gained faster than the 10 month castrates during the growing (0.75 vs. 0.61 kg/day) and finishing (0.74 vs. 0.66 kg/day) phases of the trial resulting in no weight gain differences over the entire trial period. Simi larly, Knight et al. (2000) reported a lower (P<0.01) pre weaning growth rate in calves castrated at birth compared to calves castrated at 6 and 12 months of age. Calves castrated at birth gained 1.08 kg/day pre weaning, while calves

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26 castrated at 6 and 12 months of age both gained 1.15 kg/day during this time. These difference s did not result in significant liveweight differences beyond 6 months of age. Differenc e s in pre weaning growth and weaning weight among early and late castrates may further diminish if producers administer anabolic implants at the time of castration. Heaton et al. (2006) reported no difference in pre weaning average daily gain among calves castrated at three different ages and given an implant. Bagley et al. (1989) also studied timing of castration and implant status on calf growth over a two year period. Calves castrated at birth had similar average daily gains and weaning weights c ompared to calves castrated at 4 months of age Calves administered an anabolic implant at the time of c astration weighed on average 8.2 kg heavier (P<0.01) at weaning than those not given a growth implant at castration Lents et al. (2006) conducted two different studies comparing body weight and gain in calves given an estrogenic implant and castrated pri or to or at weaning. In the first experiment, calves castrated surgically and non surgically between 2 and 3 months of age and administered a growth implant had similar weanin g weights compared to ca lves left intact until weaning. Fifty days post weaning, calves castrated surgically and non surgically between 2 and 3 months had greater (P<0.05) average daily gains than those castrated at weaning. Calves banded at weaning gained 0.43 kg/day 50 days post weaning, while calves castrated surgically and banded g ained 0.48 and 0.49 kg/day, respectively. In the second experiment, calves were banded at birth, with or without an implant, or left intact and castrated 30 days prior to weaning with an implant. No significant differences in weaning weight were detected a mong either treatment group banded at birth. However, all calves castrated at birth had heavier (P<0.01)

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27 weaning weights and greater average daily gains than the intact group during the 30 day period prior to weaning. Bulls castrated at 6 to 7 months of ag e only gained 24.1 kg during the 30 day period following castration and prior to weaning. Calves banded at birth, either receiving an implant or not receiving an implant, gained 31.3 and 35.1 kg during this same period. Marst on et al. (2003) reported simi lar findings to that of Lents et al. (2006) Calves castrated at 90 days of age and implanted had similar weaning weights to bulls left intact until weaning. Although calves castrated at 90 days of age without an imp lant weighed less at weaning than implan ted steers and intact bulls, both early castrate groups had greater (P<0.01) average daily gains during a 28 day post weaning period than bulls castrated at weaning. Calves castrated at weaning gained 1.16 kg/day during the 28 day post weaning period, whil e calves castrated at 90 days of age and either implanted or not implanted gained 1.72 and 1.52 kg/day. R esults of both studies by Lents et al. (2006) and Marston et al. (2003) indicate any weight advantage intact bulls may have over their castrated contem poraries could disappear if castration is delayed until shortly before or at weaning Other studies indicate that delaying castration beyond weaning can also erase any weight advantage intact bulls have over their castrated contemporaries. Burciaga Robles et al. (2006) reported that calves purchased as bulls tended to arrive at a feedlot environment at heavier weights (249 kg) than calves purchased as steers (238 kg). A t the conclusion of a 44 day receiving period, castrated bulls and purchased steers had similar bodyweights (307.1 kg vs. 310.0 kg) Any weight advantage the bulls had over the purchased steers was negated during the trial period because steers exhibited

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28 higher (P<0.0001) av erage daily gains and better (P<0.0001) overall health. Purchased ste ers also had reduced morbidities and mortalities, and only required on average $2.65 in medical costs per head compared to $12.30 per head for castrated bulls Newsome et al. (2010) and Ratcliffe et al. (2005) analyzed calf performance and castration statu s data over multiple years using large numbers of calves and found similar results to those of Burciaga Robles et al. (2006) Ca lves purchased as steers had greater average daily gains during the receiving periods than those purcha sed as bulls and late cas trated. Purchased steers also had lower morbidity rates and decreased treatments per animals during the trial periods. Such i ncreases in post castration weight loss and morbidity seen in older heavier cattle may be due in part to the increased stress asso ciat ed with castrating older calves. As stress increases, routine behaviors, like grazing and feed intake, as well as immune func tion may decrease (Blecha, 2000 ), inhibiting calf performance following castration. King et al. (1991) measured peak cortisol c oncentrations in c alves of two different ages (78 days or 167 days) that were left intact, surgically castrated or castrated using a burdizzo. They determined castration of 78 day old calves did not elicit a significant stress response since peak cortisol concentrations were similar between the intact calves and early castrate treatments at all time points measured. However, a rise (P<0.05) i n peak cortisol concentrations three hours post castration between intact males and late castrates was reported. Cal ves castrated surgically or by the burdizzo method at 167 days of age exhibited peak cortisol concentrations of 44.2 + 4.2 and 38.6 + 8.3 g/L three hours post castration, respectively. In contrast, bull calves exhibited a peak cortisol concentration of only 24.1 + 8.5 g/L three hours post castration. This

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29 suggests late castration may elicit a greater stress response in calves, regardless o f method used. In a review of 19 castration studies, Bretschneider (2005) concluded that stress response to castration, measured by peak plasma cortisol concentrations, was significantly higher in calves greater than 6 months of age. Stafford and Mellor (2005) also illustrated the duration of stress following castration lengthens as age at castration increases. Results measuring stress response by plasma concentrations of acute phase proteins support these conclusion s Acute phase proteins are proteins p roduced by the liver in response to stress and injury (Baumann and Gauldie, 1994). In a United States Department of Agriculture (USDA) study reported by Lyons Johnson (1998) calves castrated at birth and at 33 weeks of age had significantly lower haptoglob in (an acute phase protein) levels than those castrated at weaning at 36 weeks of age. Producers should try to minimize castration associated stress for two reasons. There are clear economic advantages to reducing stress post castration since stressed ani mals eat less, gain less, and tend to require more medical treatment Equally important, an increased concern over animal welfare and animal husbandry practices has arisen among the public. As a result, current literature on both castration method and timi ng require expansion There is a clear need to increase producer awareness and knowledge so producers can find ways to mitigate and reduce the stress associated with castration and other calf management practices whenever possible. Preconditioning Purpose Within the beef industry, p reconditioning refers to the process of weaning and preparing calves for a future phase of production (Savell, 2008). Preconditioning can

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30 vary widely in both length of time and management applied bef ore calves are marketed and sh ipped to the stocker or feedlot segment s. P rograms may consist of cas tration, dehorning, vaccination, parasite control, or a combination of such procedures. In addition, the timing at which these practices are implemented can vary from producer to producer with some procedures occurring before weaning and others occurring on the day of weaning. During preconditioning, c alves may be supplemented while in a dry lot or on pasture either a t the ranch of origin or a t a custom preconditioning yard Supplementa tion, although not always economical, can improve the nutritional status of fresh weaned calves and train them to eat from a feed bunk as they acclimate from a milk based diet to a pasture and/or grain based diet. P reconditioning also serves to minimize th e stress of weaning and reduce the incidence of respiratory disease commonly observed in nave abruptly weaned calves sold and transported through traditional marketing channels (Lalman and Smith, 2002) The concept of preconditioning calves is not new. Industry leaders, researchers and veterinarians met in the late 1960s to discuss preconditioning as a means to reduce the economic impact of bovine respiratory disease (BRD) and mismanagement in newly received feeder calves ( Gill, 1967; Schipper et al., 19 89 ) Despite the perceived benefits of preconditioning, program results have been highly variable and often conflicting (Cole, 1985) To further compound this problem, the beef industry is geographically widespread and highly diversified in operation type and management ( USDA NAHMS, 2007) creating a lack of uniformity in preconditioning programs across the country This has made producers slow to adopt preconditioning as an annual practice because they

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31 are reluctant to assume the risk and cost associated w ith holding calves for a period of time beyond weaning. At the same time, there is a growing demand for preconditioned calves in the feedlot and stocker segments. Incidence of BRD has not decreased over the years ( USDA NAHMS, 1999) despite advances in vacc ines and antibiotics available for prevention and treatment of the disease (Fulton, 2009) Additionally, survey data would suggest only half of calves placed in feedlots have received vaccinations to prevent respiratory disease prior to arrival ( USDA NAHMS 1999). It is estimated that nearly 15% of calves placed in the feedlot will develop BRD, making it the most common disease condition in United States feedlots ( USDA APHIS 2001). T reatment costs, death loss, and reductions in animal performance associat ed with BRD and mismanagement in feeder cattle continue to produce significant economic losses in the beef industry today (Fulton, 2009) In a study conducted by Fulton et al. (2002), feedlot calves treated once for respiratory disease returned approximate ly $40.00 less per head than calves requiring no treatment while on feed. In calves treated at least three times for respiratory disease while in the feedlot, returns were nearly $300 less than calves not requiring treatment. Stocker cattle returns are als o negatively impacted by morbidity, with recent data indicating a decrea se in net returns of up to 21.3% from sickness alone (Pinchak et al., 2004). Data from the Texas A&M Ranch to Rail program report similar differences between healthy and sick calves, with healthy calves returning $93/head more than sick calves (McNeill, 1999). However calves classified as healthy in these studies were not necessarily preconditioned. Nevertheless, both recent and classi cal literature would

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32 suggest health status of newl y received feeder calves is related to previous management and the practice of preconditioning. Effect of p reconditioning on c alf h ealth United States feedlot managers expect preconditioned calves to have approximately 75% fewer sick animal s and 65% fewer dead animal s than calves not preconditioned prior to placement in the feedlot (Avent, 2002). Research comparing the health of preconditioned calves and their non preconditioned counterparts would support this belief. In a three year study conduc ted by Pate and Crockett (1978), calves preconditioned and fed for at least three weeks prior to shipment had fewer (P<0.05) calves treated for sickness at the feedlot than their contemporaries shipped directly from the ranch of origin to the feedlot. Additionally, w eaned calves shipped di rectly to the feedlot had a 2.3% death loss, while preconditioned calves did not experience any death loss at the feedlot. In a review conducted by Cole (1985), data from eight large scale, controlled trials established that precond itioning reduced feedlo t morbidity and mortality by 23% and 49 % respectively. Schipper et al. (1989) reported that preconditioned calves sold through certified sales in Canada had only one half the number of feedlot treatments non preconditioned calves ha d over an eight year period. Roeber et al. (2001) reported significant differences in feedlot morbidity rates between two groups of preconditioned calves and calves of unknown origin and management procured from the auction market. Preconditioned cal ves ha d morbidity rates of 34.7% and 36.7 % while calves of unknown origin and management had morbidity rates of 77.3% Step et al. (2008) reported similar results to the previous authors between preconditioned calves that were weaned and retained on the ranch with those that were

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33 either weaned and sold directly to a feedlot or purchased at an auction market and of unknown origin. Calves that were weaned and retained on the ranch for 45 days had lower (P<0.001) rates of respiratory disease and required fewer (P< 0.05) treatments than calves shipped directly to the feedlot or purchased from the auction market. Auction market calves were reported to have nearly 42% morbidity while calves weaned and held on the ranch for 45 days only had 5.9% morbidity. Mortality rat es also differed between calf origin and weaning management, with auction marke t calves reporting a 3.1% death loss and ranch weaned calves reporting no death loss during the 42 day receiving period. Equally important, auction market calves ($13.54/head) a nd ranch calves shipped directly to the feedlot ($13.24/head) had greater (P<0.001) health costs than ranch calves weaned and preconditioned for 45 days ($8.30/head) Preconditioning also seems to improve health status as calves are transitioned from the cow calf segment to the stocker segment. Data reported by Lofgreen (1988) indicate that weaning and preconditioning calves for three weeks can reduce morbidity rates when calves are received at stockering facilities. Preconditioned calves were reported to have one third less BRD related sickness compared to non preconditioned controls. Coffey and Childs (2002) also reported differences in the incidence and treatment rate of respiratory disease in preconditioned and non preconditioned stocker cattle. Calves that were verified to have been weaned for 45 days, previously castrated, dehorned, and vaccinated required no treatment for respiratory disease during the entire stockering phase of the trial. However, approximately 9% of the non preconditioned calves req uired treatment for respiratory disease during the grazing phase.

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34 In contrast, studies exist that report no difference or even higher rates of feedlot morbidity in preconditioned calves (Swann et al., 1986; Vickers and Pritchard, 1986 ; Waggoner et al., 200 5 ) Woods et al. (1973) reported that preconditioned calves exhibited reduced (P<0.01) rates of respiratory disease in only the last year of a three year feeder calf study. The number of preconditioned calves treated for respiratory disease that year wa s 5 0% less than the number of non preconditioned calves The vaccination protocol utilized among preconditioned calves in the last year of the study included three additional immunizations against respiratory disease which were not used in the previous two y ears of the study. This may explain the difference in mortality rate for the two treatment groups during that year. In the remaining two years of the study, preconditioned calves exhibited similar morbidity rates to the non preconditioned calves. Wieringa et al. (1976) also reported similarities in respiratory disease rate between calves preconditioned for 20 days and control calves weaned and shipped directly to the feedlot. The comparable sickness between preconditioned and non preconditioned calves in t his study may be attributed to the short preconditioning period s as well as the direct shipment of control calves from the ranch of origin to the feedlot. Under normal marketing conditions, non preconditioned calves are weaned and taken to an auction barn w h ere they are comingled with unfamiliar cattle and handled nu merous times before eventual shipment to the feedlot ( USDA NAHMS, 2007; Thrift and Thrift, 2011 ) According to Abidoye et al. (2006), comingling and the number of sources within a feedlot pen ca n impact calf health and performance.

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35 In the aforementioned study (Wieringa et al., 1976) a random subset of control and preconditioned calves were placed together in a feedlot pen shortly after arrival to determine if commingling influenced health statu s of the treatment groups. Following commingling, c ontrol calves exhibited an increase (P=0.04) in the incidence of respiratory disease compared to preconditioned calves placed in the same pen C ommingled c ontrol calves exhibited a 23.5% morbidity rate, wh ile preconditioned calves in the same pen had only a 5% morbidity rate. This indicates non comingled control calves remaining separate from thei r preconditioned contemporaries and shipped directly to the feedlot may not have been challenged enough to exhib it higher morbidity rates in this study. Although some literature may suggest otherwise, it would seem that preconditioning can influence calf morbidity and mortality rates in subsequent segments of the beef industry. Preconditioning does not eliminate mor bidity and mortality within beef production, but it does reduce the rate and severity of sickness. The success of preconditioning programs may be reliant on the efficacy of vaccination protocols (Irsik, 2005; Knight et al., 1972) the amount of time spent within marketing channels as well as the disease and stress level calves are exposed to as they move between production segments ( Cole, 1985; Meyer et al., 1970 ). Because preconditioning programs typically require producers to pre wean, castrate, dehorn an d vaccinate prior to marketing, calf stress may be reduced and immunity may be improved during the initia l receiving phases when most calves tend to be at greatest risk of becoming sick ( Avent, 2002; Lalman and Smith, 2 002 ; Bailey and Stenquist, 1992 ). Red uctions in calf morbidity and

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36 mortality can not only impact profitability through reduced medicine costs and labor but th rough improved calf performance in the stocker and feedlot segments Effect of p reconditioning on c alf p erformance Health status of ca ttle upon entry to a stocker or finishing facility can significantly impact subsequent performance measures, such as average daily gain, feed intake, feed efficiency, and net return (Fulton, 2002 ; Gardner et al., 1998 ). In the Texas A &M Ranch to Rail progr am, calves identified as healthy consistently exhibited great er average daily gains and a 14% lower cost of gain while on feed than those identified as sick (McNeill, 1999). Because preconditioned calves are perceived by many in th e industry to be healthie r than fresh weaned calves lacking previous management, many feeders and buyers expect preconditioned calves to outperform their non preconditioned contemporaries (Avent, 2002) Literature measuring calf performance in subsequent production segments indic ate that preconditioned calves start on feed sooner and have higher average daily ga ins during the receiving phase than their non preconditioned contemporaries. Cole (1985) concluded that preconditioning calves prior to shipment results in higher average d aily gains and greater feed intake during the first 30 to 45 days in the feedlot. Preconditioned calves gained, on average, 1.08 kg/ day during the feedlot receiving period compared to non preconditioned controls who only gained 0.88 k g/ day (Cole, 1985) In two separat e studies conducted by Bolte et al. (2008; 2009), preconditioned calves weaned in the summer and fall exhibited higher (P<0.02) dry matter feed intakes during the first 30 days in the feedlot compared to non preconditioned controls. Additionall y, dry matter intake during the receiving period increased linearly (P=0.02) as

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37 the preconditioning period lengthened from 15 days to 60 days in the summer weaned group (Bolte et al., 2008) L ofgreen (1988) reported differences in average daily gain and f eed intake at receiving between preconditioned calves and un weaned controls. Feed intake at receiving was increased from 5.39 kg/ day in controls to 6.19 kg/ day in preconditioned calves, while average daily gain for controls w as 0.25 kg/ day less than calve s preconditioned for 21 days prior to shipping Preconditioning also resulted in improved feed conversion rates during the receiving period Calves shipped directly to the feedlot at weaning required 3.69 kg of feed to produce one kg of gain, while precond itioned calves only required 3.05 kg of feed to produce on kg of gain. Seeger et al. (2008) evaluated the performance of calves of unknown health history purchased at an auction market to preconditioned calves sold through certified sales. The precondition ed calves were separated into two treatment groups based on the health program they were administered H owever, all preconditioned calves were weaned for 45 days, treated for parasites, and vaccinated against respiratory disease before sale and arrival at the feedlot Calves in both preconditioning treatment groups significantly outperformed the calves of unknown health history during the 28 day feedlot receiving phase of the trial. Calves of unknown health history only g ained 1.60 kg/ day from arrival to th e second processing while precondit ioned calves gained 1.80 kg/day and 1.76 kg/ day. Dry matter intake during receiving also was affected by treatment (P<0.05) with precondition ed calves consuming 7.35 kg/ day an d 7.60/ per day and auction mark et calves con suming 6.29 kg/ day. These differences in performance

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38 between weaning and health programs resulted in fewer (P<0.05) days on feed for preconditioning groups. Improvements in calf performance during the receiving phase are generally attributed to the precond reduced stress upon arrival from the pre weaning process. Most preconditioning programs provide supplementation to calves following weaning, providing a relatively easy transition from nursing to fi nishing whe re they are fed a similar diet. Enhanced nutritional status and adaption to high energy concentrates prior to shipping facilitates calf growth early in the finishing period I n some cases, the trend for higher rates of gain and other measures of performance are not be limited to this short receiving interval. In a large scale study comparing feedlot performance of single sourced preconditioned and non preconditioned calves, Cravey (1996) reported significant differences in average daily gain da ys on feed, and feed conversion measures during the cumulative feeding period Pre conditioning improved average daily gain by 0.09 kg/ day and dry matter feed conversion nearly 9% reducing the feeding period by 40 days for preconditioned calves. In a simil ar large scale study evaluating feedlot performance of preconditione d and non preconditioned calves, average daily gain was improved 10% and dry matter feed conversion improved from 2. 93 kg of feed per kg of gain to 2 .72 kg of feed per kg of gain by precon ditioning (Cravey, 1996) In both studies, preconditioned calves exhibited heavier harvest weights while requiring less feed and fewer days on feed than their non preconditioned contemporaries. These results agree with those reported by other authors eval uating cumulative feedlot performance in preconditioned calves. Pate and Crocket (1978) reported an

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39 11 % increase in rate of gain over the entire feeding period for calves preconditioned on the ranch for 24 days. Macek et. al. (2011) reported significantly faster feedlot gains, fewer days to harvest, and heavier harvest weights in calves preconditioned for at least 45 days prior to arrival at the feedlot. Seeger et al. (2008) reported calves preconditioned for 45 days gained 1.56 kg/day and 1.55 kg/ day over the entire feeding period, while calves of unknown he alth history gained 1.50 kg/ day from arrival to harvest. In contrast, Pritchard and Mendez (1990) reported no difference in cumulative average daily gain for preconditioned and non preconditioned calves P reconditioned calves also exhibited poorer feed conversions, requiring 6.44 kg of feed per kg of gain while non preconditioned calves only req uired 6.24 kg of feed per kg of gain. Similarly, Bolte et al. (2009), Lofgreen (1988), and Cole (1985) reported no differences in rate of gain and feed conversion ratios across the entire feeding period among preconditioned and non preconditioned controls Although preconditioned calves in all of these studies out performed their non preconditioned contemporaries du ring receiving, the authors failed to find significant performan ce differences across the growing and finishing phases of feedlot production. This may be attributed to compensatory gain in non preconditioned calves as they overcome the stress of weaning an d adapt to a high concentrate diet following receiving The impact of preconditioning calves on subsequent performance is somewhat variable, and may be dependent upon calf type, calf condition, year effects, and preconditioning method I t seems preconditio ned calves hold a performance advantage to fresh weaned calves of unknown health history following their arrival at stockering

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40 and finishing facilities However, their ability to outperform their non preconditioned contemporaries throughout the entire feed ing period is less clear Regardless, i mprovements in gain, feed conversion, and intake during receiving all contribute to lower days on feed and reduced costs of gain. With more desirable measures of growth and reduced mortality rates preconditioning may also influence the subsequent carcass quality and value of calves. Effect of p reconditioning on c arcass a ttributes Carcass quality and consistency in beef production ha ve become a focus within the industry in recent ye ars. Increases in the number of catt le sold on a carcass m erit basis and through USDA certified brands have established a clear need for producers and feeders to manage cattle in a way that will improve quality and palatability attributes in fed cattle (Smith et al., 2005) Numerous factors have been shown to impact the subsequent carcass composition of beef calves, including previous management, disease, and stress level (Gardner et al., 1999; M itlohner et al., 2002) Management practices such as castration and dehorning have been shown to positively influence USDA quality grade and palatability (Field, 1971; Jacobs et al., 1977) Research comparing castrated ma les to intact males show steers produce more USDA Choice carcasses and meat consumers find to be more palatable than that produced b y bulls (Champagne et al., 1969) C astration and dehorning have also been shown to consistently reduce the incidence of quality defects in fed cattle suc h as bruising and dark cutters (Fie ld, 1971; Seideman et al., 1982 ). Additionally, evidence exists that when castration and dehorning are implemented prior to weaning, less stress is imposed on the calf morbidity is decreased, and fewer carcass quality defects result (Burciaga Robles et al., 2006; King et al., 1991)

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41 T he practice of vaccination is also as sociated with improve d carcass quality since it can enhance the health status of recently weaned calves and is a critical component in the effort to prevent respiratory disease (Knight et al., 1972; Macek et al., 2011; Snowder et al., 2006). Literature doc umenting the relationship between calf health and subsequent carcass quality clearly shows that healthy cattle outperform cattle requiring treatment. Harvested cattle with a history of respiratory disease consistently produce lower quality carcasses and to ugher meat (Gardner et al., 1999; McNeill, 1999; Roeber et al., 2001), which can significantly reduce their carcass value (Gardner et al., 1998). Many preconditioning programs stipulate calves must be castrated, dehorned, and vaccinated prior to sale, maki ng preconditioned calves appealing to buyers who understand the connection between pre finishing management, disease, stress level, and carcass attributes. Although literature comparing carcass composition and quality among healthy and sick cattle abounds, carcass data comparing preconditioned calves to their non preconditioned contemporaries is somewhat limited. R esearch available on the subject does indicate preconditioned calves tend to produce carcasses with more positive attributes that influence profi tability, such as degree of marbling, USDA quality grade, and hot carcass weight. Seeger et al. (2008) reported that two treatment groups of preconditioned calves produced approximately 22% and 26% USDA Choice or Prime carcasses, while calves of unknown he alth history only produced 17% USDA Choice or Prime carcasses ; a 35% improvement from preconditioning All treatment groups had similar dressing percentages, hot carcass weights, and produced the same percentage of USDA Yield Grade 1 and 2 carcasses.

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42 Abid oye and Lawrence (2006) evaluated the performance of cattle that were preconditioned on the ranch of origin to cattle sourced from multiple ranches, commingled and backgrounded prior to entering the feedlot. Preconditioned cattle were castrated, dehorned, immunized, and weaned no less than 28 days prior to arrival at the feedlot. The authors reported that preconditioned cattle had a greater percentage of calves grading USDA Choice or Prime compared to calves that were comingled and backgrounded prior to fee dlot entry. Approximately 40% more single source, preconditioned cattle graded USDA Prime than backgrounded cattle, while 128 backgrounded cattle and only 27 single source, preconditioned cattle graded USDA Standard In a study conducted by Waggoner et al (2005), calves were allocated to four preconditioning periods to evaluate the duration of time spent between weaning and feedlot entry on performance and carcass characteristics. Calves were preconditioned for 0 to 20 days, 21 to 40 days, 41 to 60 days, or greater than 61 days before arriving at the feedlot. C alves preconditioned for at least 21 days had heavier (P=0.06) hot carcass weights than calves preconditioned for 0 to 20 days and marbling score increased linearly (P<0.01) as preconditioning durat ion increased. Measures of back fat and calculated yield grade also increased as preconditioning duration lengthened; however, all treatment periods produced USDA Yield Grade 2 carcasses. Calves preconditioned for less than 2 1 days produced the lowest value carcasses among the treatment groups, earning only $111.77/45.4 kg compared to $114.91/45.4 kg earned by calves preconditioned for 41 to 60 days. Additionally, net income for calves preconditioned for

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43 less than 21 days was $41.66/head, while net income f or calves preconditioned for 41 to 60 days was $2.23/head. Macek et al. (2011) also reported heavier (P<0.02) hot carcass weights for calves weaned and preconditioned for 45 and 15 days compared to calves weaned for 0 days and shipped directly to the feed lot. H owever, Macek et al. (2011) did not report differences in marbling score, USDA yield grade or twelfth rib back fat like the previous authors Pate and Crockett (1978) reported preconditioned calves and their non preconditioned contemporaries produced carcasses with similar dressing percentages and of the same quality grade. Similarly, Roeber et al. (2001) did not report differences in hot carcass weight, marbling score, and carcass value between preconditioned calves and calves of unknown origin and m anagement procured from an auction market. Ca lves from both the certified preconditioned program and the auction market produced carcasses with marbling scores between Small 00 and Small 27, qualifying both groups for USDA Choice carcasses. Literature eva luating preconditioning and its effect on subsequent carcass composition is both limited and variable. It would seem that because preconditioned calves have undergone managemen t practices designed specifically to reduce stress and improve health that these calves would produce higher quality carcasses on a consistent basis. Industry perceptions seem to support this idea. According to Avent (2002) feedlot operators expect preconditio ned cattle to produce nearly 30% more USDA Choice carcasses than non precond itioned calves. However, c urrent literature is only indicative of such an association, illustrating a need for further research to support such perceptions

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44 Effect of p reconditioning on c alf s tress Calves can be subjected to a variety of stressors through out their life, with many of these stressors occurring at or around the time of weaning. Although practices such as castration, dehorning, weaning and handling are all considered standard management processes each of these events can be stressful ( Carrol l and Forsberg, 2007 ) Castration and dehorning are considered to be physical stressors since they can cause temporary pain to cattle undergoing these procedures (Grandin, 1997) Stressors like handling, restraint, and transport are classified as psycholog ical since a pain response is not necessarily invoked, but a fear response is (Grandin, 1997) Weaning can challenge calves from both a physical and a psychological standpoint as they are often forced to rapidly transition away from a milk based diet, are permanently separated from their dam transported off the ranch of origin and comi ngled with unfamiliar cattle in unfamiliar environments ( Arthington et al., 2003; Grandin, 1997 ; Kim et al., 2011 ). These concepts are important because stress can negativel y impact the ability of calves to resist disease and exhibit favorable performance gains post weaning. In animals, stress activates both the sympathetic nervous system and the hypothalamic pituitary adrenal (HPA) axis in what is commonly referred to as a n euroendocrine response (Breazile, 1988; Murata, 2007). As a result, catecholamines and glucocorticoids are released, which then act on a variety of target organs and tissues in an attempt to help the animal regain homeostasis (Carrol and Forsberg, 2007; Mu rata, 2007). Although such a response is designed to help protect animals undergoing stressful situations, these reactions may actually impair immune function and increase the likelihood of disease in animals that experience stress over extended periods of time (Aich et al., 2009; Blecha, 2000; Breazile, 1988). Additionally, stress may alter appetite

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45 and the nutritional requirements of animals, which if not met, could further suppress an and Forsberg, 2007; Hutcheson and Cole, 1986). Many of the fresh weaned calves that arrive at stockering and finishing facilities in the United States are in such a stress induced state (Carroll and Forsberg, 1997) The practices of weaning, castration, c omingling, and long haul transport all occur within in a short period of time for many calves in the beef industry. As calves become stressed from these management and marketing practices, normal activities such as eating or drinking may cease and immune f unction may become impaired as they attempt to c ope and reestablish homeostasis. This results in a weakened immune system and poor nutrition al status making fresh weaned calves highly susceptible to respiratory illness and death after arrival As a resul t the concept of preconditioning evolved around alleviating calf stress as a means to improve calf health and performance. The practice of preconditioning provides calves with a period of time to overcome the physical and psy chological stresses associated with weaning and calfhood management before they are transported and comingled in subsequent industry segments. Additionally, when combined with supplementation and an effective vaccination program preconditioning can ease the stress associated with rapi d diet change and inadequate feed consumption while enhancing the immune system at a time when calves are at the highest risk of becoming morbid. Many within the industry recognize the benefits associated with preconditioning and its ability to mitigate st ress ( Avent, 2002 ; Lalman and Smith, 2002 ) which has prompted researchers to both quantify and compare the

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46 stress response of precondition ed calves to more traditional methods of weaning and marketing. One way to measure stress at weaning is through beha vioral changes that occur when the maternal bond is disrupted and calves ad apt to a new diet (Herzog, 2007 ). Pri ce et al. (2003) used behavior as an indicator of weaning stress during a three year study evaluating five wean ing strategies Treatments includ ed non weaned controls on pasture, fenceline separation from dams while on pasture, non preconditioned calves under total separation from dams while on pasture, preconditioned calves under total separation from dams in a drylot, and non preconditioned calv es under total separation from dams in a drylot. Preconditioned calves received alfalfa hay in the drylot for 10 days prior to weaning. Althou gh non weaned control s and fenceline weaned calves were reported to be under less stress than calves under total s eparation, preconditioned calves under total separation spent more time eating walked the fenceline less, and laid down more than non preconditioned calves under total separation Additionally, preconditioned calves under total separation vocalized less t han non preconditioned calves under total separation Preconditioned calves were reported to ha ve an average of 371 vocalizations per hour per 10 calf group over the three year study Non preconditioned calves under total separation were reported to have a n average of over 518 vocalizations per hour per 10 calf group and nearly 435 vocalizations per hour per 10 calf group for calves on drylot and pasture, respectively. O bserving behavioral changes can be useful in determining if an animal is stressed follow ing implementation of a management practice like weaning Unfortunately, there are distinct shortcomings in using behavior as a sole means of

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47 quantitative measurement in stress studies. Some practices or events do not necessarily elicit a behavioral change even if the animal is stressed, nor is a particular behavior exclusive to a specific type of stressor (He rzog, 2007 ). As a result, m any researchers prefer to use physiological parameters, such as stress response chemicals and hormones, as markers of stres s in animals. Traditionally, the glucocorticoid s cortisol and corticosteroid have been used to measure stress responses in c attle and other livestock undergoing specific manage ment practices Wieringa et al. (1976) evaluated the effect of preconditioning o n plasma corticosteroid levels in Hereford calves being weaned and shipped to the feedlot. Preconditioned calves were weaned three weeks before all calves were transported directly to the feedlot. Preconditioned calves exhibited lower (P<0.05) plas ma corti costeroid levels both prior to transport and during transport to the feedlot compared to freshly weaned control calves Control calves had plasma corticosteroid levels of 4.18 g/100 mL on the day prior to transport, while preconditioned calves had plasma corticosteroid levels of 3.25 g/100 mL prior to transport. Differences in corticosteroid levels prior to transport may be attributed to both the adjustment period of precondit ioning and handling differences between treatment groups when blood samples were collected. Control calves had to be brought from the pasture to the working pens and sorted from their dams prior to bleeding unlike preconditioned calves that experienced sim ilar conditions three weeks prior and were already at the pens for sample collection. This may be an important factor for producers to consider when deciding to wean and precondition calves. For producers not opting to precondition, the stresses associated with maternal separation, dietary change, and

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48 added handling and processing on the day of weaning may not be separated from the stress directly associated with transport in freshly weaned calves like they can be preconditioned calves. In contrast, Herzog (2007) evaluated measures of stress during weaning and reported similar serum cortisol levels between abruptly weaned calves, preconditioned calves, and non weaned control calves. Serum cortisol concentrations for each trea tment group averaged 60 nmol/L pr ior to weaning on day 0, which acted as a baseline control measure. The cortisol concentrations reported for day 1, 2, and 3 following weaning did not rise above this baseline average for either of the treatment groups. Additionally, cortisol concentration s within each treatment did n ot increase from day 0 to day 3 following weaning when collections ceased. It should be noted that cortisol concentration s were taken only once per day in the morning, which could indicate why the reported cortisol concentratio ns failed to denote weaning related stress or differences in stress level between weaning treatments. Although c ortisol is a useful measure of adrenal response during short term stress caution must be exercised when using and interpreting cortisol measure ments in the literature. C ortisol secretion from the adrenal gland is highly dependent on sampling time and method, circadian rhythms, reproductive state, sex, and genetics (Grandin, 1997 ). T he release of adrenocorticotropic hormone (ACTH), which acts on t he adrenal gland to promote secretion of glucocorticoids, also changes over time and can take as long as 20 minutes to peak making single measurements of serum cortisol unreliable (Grandin, 1997). As a result, researchers have begun to report changes in t he immune

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49 system as a means to measure stress more accurately including increases in positive acute phase protein (APP) profiles. Acute phase proteins are produced by the liver during the acute phase response (APR) when an animal experiences stress. Orig inally, the APR was thought to be elicited by the release of pro inflammatory cytokines specifically as a result of an injury or infection in the animal ( Baumann and Gauldie, 1994; Carrol and Forsberg, 2007). These pro inflammatory cytokines will then trav el to the liver and regulate the release of APPs from hep atocytes (Petersen et al., 2004) The APR facilitates the healing process and allows animals to reestablish homeostasis during stressful periods (Lomborg et al., 2008). Recently, however, the APR is thought to be elicited by psychological stressors in addition to physical stressors like injury or infection (Murata, 2007). Although the exa ct mechanism underlying this stress induced APR in not entirely clear, Murata (2007) hypothesizes that the activa tion of the HPA axis and subsequent release of glucocorticoids induce production of APPs within the liver. This hypothesis is supported by both in vitro lab experiments (Higuchi et al., 1994 ) and applied animal research studies in which food animal species were exposed to various psychological stressors and subsequently exhibited changes in APP production (Arthington et al., 2003; Gymnich et al., 2003; Kim et al., 2011) The p roduction of APPs can be measured through blood serum concentrations, which wil l either substantially increase above baseline levels in response to stress as in the case of positive APPs, or decrease below baseline levels in the case of negative APPs (Carrol and Forsberg, 2007; Petersen et al., 2004) Serum concentrations of

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50 APPs al low researchers to quantify the stress associated with a particular practice, much like serum concentrations of glucocorticoids or catecholamines. The primary advantage to utilizing APPs over that of more traditional measures of stress, like cortisol, are their longer half lives and latency to peak, which provides researchers with a broader sampling window to collect blood serum from animals (Slocombe and Colditz, 2005). Ceruloplasmin and haptoglobin are two positive APPs currently used to measure and evalu ate stress in food animal species. Arthington et al. (2008) evaluated stress in steers allocated to four different weaning programs prior to shipment using ceruloplasmin and haptoglobin Weaning treatments included control calves weaned on the day of trans port, calves provided ad libitum access to creep feed prior to weaning and shipment, calves preconditioned for at least 45 days prior to shipment, and early weaned calves removed from their dam at 70 to 90 days of age. Preconditioned calves were reported t o have a reduced (P=0.08) increase in plasma haptoglobin conc entrations compared to control and c reep fed calves weaned and shipped on the same day. Haptoglobin concentrations increased from day 0 to day 1 for all treatments. However, preconditioned calves exhibited an increase of 1.50 units during this time period, while fresh weaned controls and creep fed calves exhibited increases of 2.15 and 2.63 units of, respectively. Additionally, preconditioned calves generally had lower ceruloplasmin concentrations than creep fed calves throughout the trial, while early weaned steers also had lower (P<0.10) cerulop lasmin levels on days 8, 15, 22 and 29 following shipment compared to fresh weaned control calves.

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51 Campistol (2010) also measured the acute phase respon se in calves during a 42 day preconditioning trial. Calves were initially allotted to one of two pre weaning treatments ; supplemented and unsupplemented Supplemented calves were given a high fiber supplem ent one week prior to weaning, while un supplemented calves did not receive any supplementation prior to weaning. At weaning (day 7 ) each pre weaning treatment was subsequently split into two post weaning treatments based on weaning strategy. Calves were either weaned using total separation from dams for t he entire preconditioning period or weaned using fenceline separation for 14 da ys before being moved to total separation for the remainder of the preconditioning period. Regardless of pre weaning treatment or weaning strategy, all calves received supplemen t f rom day 7 to day 21 of the trial period. Campistol (2010) reported that a ll calves exhibited a post weaning increase (P<0.01) in haptoglobin, regardless of pre or post weaning treatment. Haptoglobin levels across all treatments were returned to pre we aning levels by day 14 of the preconditioning period suggesting the practice of weaning is a long term stressor in beef calves Although n o pre weaning or post weaning treatment differences were reported for haptoglobin response ceruloplasmin levels were less (P=0.02) at weaning (day 7) for unsupplemented calves compared to supplemented cal ves. Additionally, calves in this unsupplemented pre weaning treatment group who were under total separation during the entire preconditioning period exhibited lower (P =0.04) ceruloplasmin levels on day 21 than calves in this same pre weaning treatment group that were under fenceline separation for a portion of the preconditioning period.

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52 Both stu dies conducted by Arthington et al. (2003) and Campistol (2010) suggest pr oviding calves with a pre weaning supplementation may not help mitigate the stressors associated with weaning, which include maternal separation, social re organization, and cessation of nursing. Additionally, a two part weaning strategy consisting of fenc eline separation followed by transport to another location for total maternal separation may lengthen the period calves are under weaning related stress. Unfortunately, the study conducted by Campistol (2010) lacked both a non weaned control group and a fr esh weaned treatment group that could be used to compare stress response in preconditioned calves to more traditional methods of weaning and marketing. Although calves were not preconditioned, Vendramini and Arthington (2007) evaluated post transport and feedlot receiving stress of early weaned calves offered a yeast fermentation product Calves were weaned at an average age of 66 days weighing approximately 84 kg each. Following weaning, calves grazed ryegrass and stargrass pastures for a total of 224 day s before simulating transport to a feedlot. Treatments during the grazing period included a control group offered concentrate supplement only and a treatment group offered the same concentrate supplement with a yeast fermentation product. The authors repor ted similar performance responses during the grazing period for both treatment groups. At the conclusion of the grazing period, half of each grazing supplemented group was loaded onto a trailer and transported for 24 hours before being returned to the rese arch facility. Following the transport simulation, all calves were placed in a drylot for 30 days and offered one of two diets in a 2 x 2 factorial design. Half of the calves transported

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53 received the concentrate supplement offered in the grazing period alo ne, while the remaining half received the concentrate supplement with added yeast fermentation product. Similarly, calves not subjected to the transport simulation were allocated to either a supplemented control or supplement with additive treatment. Altho ugh transportation reduced (P<0.01) calf body weight in the first 24 hours of the feedlot receiving period, calf performance for the remaining 30 day receiving period was not influenced by either transport or yeast supplementation. Likewise, haptoglobin an d ceruloplasmin concentrations were similar between all treatments, indicating transportation and yeast supplementation did not influence calf stress levels during this trial. Haptoglobin and ceruloplasmin concentrations were influenced by sampling day, r egardless of treatment. Increases (P<0.05) were observed in haptoglobin from day 5 through day 9, while ceruloplasmin increased (P<0.05) from day 9 through day 16 of the receiving period. Since non transported calves exhibited similar increases in acute ph ase concentrations, increases in stress cannot be attributed solely to transportation in this study. Additionally, calves had been weaned for over 200 days before simulated transport and transition to a feedlot like environment. This also suggests weaning may not have been the sole stressor eliciting the inflammatory response in this group of early weaned calves. As a result, the transition from a grazing environment to a drylot environment typical of many feedlots may have resulted in an increase in calf stress as calves. This is important and may indicate why preconditioning studies report inconsistent results in calf stress and subsequently performance. Although preconditioning may help separate

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54 weaning and transport stress this early weaning trial indi cates weaning for a n extended period of time may not completely prevent stress as calves experience transitions in environment and large increases in concentrate level in their overall diet. Numerous studies have successfully established that weaning, tran sport, castration, and restraint all increase stress markers in calves (Zavy et al., 1992). At the same time, it is apparent little has been done to determine how preconditioning influences indicators of s tress in weaned calves, either through changes in b ehavior or physiological parameters Additionally, literature available on preconditioning and its ability to mitigate stress in feeder calves is somewhat vague and utilizes a variety of methods that may not accurately assess stress. Further research in th is area is warranted to determine if the success of preconditioning is due in part to the alleviation of stress at weaning prior to shipment and comingling Effect of p reconditioning on c alf v alue Feeder c alf value is influenced by a variety of factors, in cluding weight, sex, condition, lot size, uniformity, health, and previous management (Avent, 2002). Under normal market conditions feeder calf prices will increase as calf weight decreases, and lot size and uniformity increase (Avent, 2002 ) Buyers also t end to pay more for castrated steers than heifers, with significant discounts occurring for intact males and calves with horns (Troxel and Barham, 2007 ) Additionally, calves that are perceived to be healthy or in a condition that would facilitate compensa tory gain are priced more favorably than calves perceived as in condition (Avent, 2002 ) Preconditioning calves can influence each of these factors, subsequently influencing the price producers are offered for calves in a given production year. Preconditioning provides producers with a n extended period of time to implement

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55 management practices, such as castration, vaccination, and dehorning, which can help producers avoid unnecessary discounts at the market The preconditioning period also provides calves with an extended period of time to overcome the stress of weaning, adapt to a dry diet, and gain weight through supplementation. In combination with proper management, this can significantly improve health, condition, future per These improvements in health and performance are the primary reason stockers and feeders are willing to pay premiums for preconditioned calves. As the number of animals pulled and treated for disease declines, medicine cost and associated costs like increased labor, lost performance and reduc ed end product quality also decrease (Duff & Galyean, 2006), justifying premiums offered for preconditioned cattle. According to Avent (2002), feedlot managers per ceive that preconditioned calves are worth a premium of $0.116 / kg over that of si milar, non preconditioned calves Recent market data support this, reporti ng actual premiums up to $0.174 / kg for preconditioned calves sold through verified programs (King and Seeger, 2005). For calves weighing approximately 227 kilograms, this premium would equate to nearly $40/ head. Substantial premium s however, are not always observed in the marketplace Avent (2002) reported premiums for preconditioned calves sold in Jopl in, Missouri and at Superior Livestock only ranged from $0.043/ kg to $0.074 / kg which are well below the premium feeders reported they were willing to pay in the same study Donnel l et al. (2007) reported calves sold through Noble Foundation cooperators in Oklahoma received premiums averaging only $0.0 94/ kg Similarly, Lalman and Smith (2002) r eported premiums as low as $0.061 / kg.

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56 Although counter intuitive, preconditioning premiums also seem to decrease during periods of high feeder calf market prices (Dh uyvetter et al., 2005). As calf prices increase, calves, regardless of previous management, become more valuable than they would other wise be in a down market. As a result, d eath loss and reductions in performance due to stress, sickness, or lack of previo us calfhood management become more expensive in high markets This should increase the incentive for feedlots and stockers to pay more for preconditioned calves than their non preconditioned counterparts as cow calf producers assume some of the risk associ ated with morbidity and m ortality during the preconditioning period (Bailey and Stenquist, 1992). However, this is not always the case. In 2005, Dhuyvetter et al. reported an inverse relationship between feeder calf futures price and preconditioning premiu ms calves earned during special calf sales over a 6 year period As a result participation in pr econditioning programs often decline during periods of high feeder calf prices (Lalman and Smith, 2002) due in part to lower premiums In addition, cow cal f p roducers lack the incentive to assume the risk and additional costs as sociated with preconditioning when feeder calf prices are high and the market is un willing to distinguish between preconditioned and non preconditioned calves Increased risk for cow cal f operators and the d iscrepancies that exist between the perceived or expected value of preconditioned calves and the price paid in the marketplace may explain why cow calf producers choose not to precondition calves beyond weaning (Dhuyvetter et al., 2005 ). The primary reason these discrepancies continue to exist in the marketplace is that feeder calf buyers still bear some risk when purchasing preconditioned calves

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57 (Avent, 2002 ; Dhuyvetter et al., 2005 ). Currently, there are a variety of preconditioning p rograms that exist within the industry, resulting in a lack of uniformity from one pr otocol to the next. Additionally, d iscerning previous management within the traditional market ing arena is often difficult and flawed Buyers are typically uncertain about the characteristics of feeder calves sold through auctions which forces buyers to price calves based o n the average quality within that particular market place and time (Bulut and Lawrence, 2006) C ommunication w ithin the market can also breakdown and fe eders cannot be assured cow calf producers followed a specific protocol for minimum weaning period or vaccine handling and administration The information asymmetry created when sellers fail to verify calf quality or previous management increases the risk associated with purchasing feeder calves which ultimately results in order buyers pricing preconditioned calves below their expected value. As a result, producers have begun to market preconditioned calves through third party certified sales Certified sa les help to correct asymmetry within the marketplace by offering buyers and feeders some assurances when purchasing preconditioned feeder calves (Bulut and Lawrence, 2006). Calves enrolled in these marketing programs are required to undergo a specific wean ing and preconditioning protocol, of which a third party certifies Over time, many of these programs establish a positive reputation within the industry (Avent, 2002), allowing feeders and order buyers to price preconditioned calves enrolled in these cert ified program s at a premium that reflects their true value within the marketplace. Bulut and Lawrence (2006) examined this concept by assessing the value of third party certification for preconditioned calves sold through Iowa auction markets.

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58 Compared to base calves lacking a third party weaning and vaccination certification claim preconditioned calves with a certified vaccination claim and certified weaning claim of at least 30 days received a $0.135/kg premium or for a 227 kg calf, a premium exceeding $30/ head. At the same time, calves with partially certified preconditioning claims received premiums above the base price but significantly less than those earned by third party certified calves for vaccinations and weaning Calves with a minimum 30 day weaning certification, but no vaccination certification received a $0.075/kg premium. Calves with a certified vaccination claim, but no certified weaning claim received a similar premium of $0.069/kg which is nearly half of the premium completely certifie d calves received in the same market The authors also assessed whether the premiums associated with third party certification cover the cost of participation in third party preconditioning programs. Bulut and Lawrence (2006) estimated the cost of third p arty certification would not exceed $ 0.022/kg for calves averaging 227 kg. According to recent market data (Bulut and Lawrence, 2006; Donnell et al., 2006; King and Seeger, 2005), the premiums earned through third party certification sufficiently cover thi s cost. Additionally, market data reported by Bulut and Lawrence (2006) indicate that buyers do not necessarily distinguish between part ial and uncertif ied preconditioning claims result ing in a significant value loss regardless of the effort producers hav e made to improve calf quality This suggest s participation in third party programs are a worthwhile investment for producers opting to precondition calves This concept is further supported by market data Preconditioned Health ( CPH 45) program. Laurent (2011) reported net estimated

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59 returns for producers enrolled in the CPH 45 sales averaged $59.36/ head at two market locations over an 18 year period, with negative returns occurring in only two of the 18 year s. In four of the years estima ted net returns exceeded $80/ head for producers opting to hold calves and market at least 45 days after weaning Specifically, in 2005, returns were estimated at over $100/ head for calves held and sold in the December market weighing approximately 45.45 kg more than if they were weaned and immediately sold in the October market when calf supply was greater Simi larly, Donnell et al. (2007) reported net returns for multiple preconditioning programs, including the Noble Foundation and Oklahoma State University cooperator sale. Cooperators participating in the Noble Foundation sales during 2004 and 2005 earned estimated ma nagement premiums of $0.094/ kg, resultin g in a net return of $57.31/ head when producers marketed heavier calves approximately 52 day s after weaning. Dhuyvetter et al. (2005) reported preconditioned calves sold through special calf sales were priced significantly higher than non preconditioned calves sold through traditional auction market sales. On average, preconditioned calves sold f or $0.102/ kg more than their non preconditioned contemporaries sold from fall 1999 to winter 2004. Producers that preconditioned added an estimated 30 kg of additional body weight, that when sold in the November December market resulted in an estimate d net return of over $14/ head. One of the benefits to preconditioning explains this trend. W hen supplementation is offered during the preconditioning period, cattle can both regain weight lost due to the stress of weaning and gain weight over that of their orig inal weaning weight Although heavier weight calves tend to be priced lower in the marketplace, this is often offset by

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60 the seasonality of market prices and premiums associated with preconditioning ( Avent, 2002; Dhuyvetter et al., 2005 ) Producers that opt to precondition will typically sell their calves at least one month later than they would have if they opted to sell calves directly at weaning. For producers with spring calving seasons, which is the majority of cow calf producers in the U nited S tates ( M cBride and Mathews, 2011), this means marketing preconditioned calves in the November December market. Feeder calf prices during this period are typically more favorable than the September October market fresh weaned calves are sold in ( Dhuyvetter et al., 2005 ). Preconditioning allows producers to capitalize on more favorable feeder calf prices with heavier weight calves due to seasonality and changes in feeder calf supply and demand. Preconditioning has several benefits, of which feeder calf buyers and fee ders recognize. Improvements in health, implementation of castration, dehorning, and vaccination, as well as the opportunity to mitigate weaning associated stressors prior to transport make preconditioned calves desirable to operators in subsequent industr y segments. As a result, buyers have become increasingly willing to offer premiums for preconditioned calves, especially if producers can offer feeders and stockers assurances related to previous management and vaccination protocols. H owever, information a symmetry and market conditions may not always result in premiums or premiums sufficient enough to cover the risk and associated costs of preconditioning. This forces cow calf producers to evaluate preconditioning on an annual basis as cost of production, p roducts available, and market dynamics fluctuate Factors Influencing Preconditioning Economics and Profitability Several factors must be taken into consideration when making the decision to precondition, including current market prices, forage availabili ty, on farm infrastructure

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61 and f eed costs. According to recent data, approximately half of calves sold from cow calf operations in the United States are sold at weaning, while the remaining half are held on the ranch of origin for precondition ing ( USDA NA HMS, 2007) However, these proportions change from year to year as market factors weather, and preconditioning costs change. In 2009, nearly 60% of cow calf operations in the United States decided not to precondition calves and instead sold calves at wean ing (McBride and Mathews, 2011). This was due in part to relatively low feeder calf prices, increasing feed and fertilizer prices and a weak and uncertain 2009 consumer economy ( USDA ERS, 2011 ). T he likelihood a specific cow calf operation will precondit ion in a given year can also be eographic location within the country In 2009, 70% of cow calf farms located in the Southeast ern region of the United States cho se not to precondition compared to only 41% of operations in the Northern Plains (McBride and Mathews, 2011). Geographic proximity to subsequent segments of the industry, feed and forage availability within a particular locale, and environmental constraints on production may make holding and supplementing calves beyond weaning less feasible for some cow calf producers than others. In addition, an inverse relationship seems to exist between herd size and likelihood of preconditioning In 2009, nearly two thirds of farms with less than 50 head of cows opted not to precond ition, while nearly two thirds of farms with greater than 500 cows opted to precondition (McBride and Mathews, 2011). Larger operations are more likely to have a defined calving season, practice better pasture management and record keeping, as well as vacc inate and utilize technologies like implants and ionophores

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62 (McBride and Mathews, 2011 ; USDA NAHMS, 2007 ). A ccess to better quality forage and beef technologies facilitate calf performance during preconditioning, while shorter calving intervals provide pr oducers with a larger, more uniform calf crop to market following the holding period. Of these factors, cost is probably the greatest single factor driving the decision to precondition Cow calf producers can incur large costs while preconditioning calves including feed, labor, vaccinations, and at times medicine and death loss Although most progra ms average slightly over $1/head/ day (Donnell et al., 2007), est imates range between $35/head and $75/ head for some programs (Avent, 2002; Lalman and Smit h, 200 2 ; Ward and Lalman, 2003). Vast differences in program costs can be dependent upon the preconditioning system utilized, length of time calves were preconditioned, feed costs, and rate of gain (Donnell et al., 2007) Preconditioning s ystem Preconditioning can be implemented on either a pasture based system or a dry lot based system, each with their own advantages and disadvantages. According to Mathis et al. ( 2009 ) p asture based systems seem to reduce stres s in freshly weaned calves. In this system, the pos t weaning environment is similar to the pre weaning environment resulting in less of a dietary change as calves continue to have pasture access for grazing Although calves in a pasture based system seem to benefit from this familiar environment, drylot s ystems tend to produce greater gains post weaning due to the provision of supplementation (Mathis et al., 2009). Supplementation offered in dry lot systems can be forage based; however, it is often a high energy concentrate ration, which can also increase t he cost of preconditioning.

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63 Although few studies have sought to compare these preconditioning systems in a controlled experimental setting, t hese g eneralizations have recently been supported by work at New Mexico State University Mathis et al. (200 8 ) ran domly assigned calves of similar weaning weights to either a pasture based or drylot based system to compare calf performance and profitability over a three year period. Pastured calves remained on native New Mexico range and were supplemented with a 32% c rude protein range cube three times per week while drylot calves received a corn wheat middlings based pellet and alfa lfa hay each day. During the 42 day preconditioning period, calves under intensive drylot management exhibited greater (P<0.01) ADG, resu lting in heavier (P=0.03) body weights at the conclusion of the preconditioning period. Although drylot calves gained more and weighed more at the conclusion of the preconditioning period, net income per head was $45 greater (P<0.01) for calves managed on a pasture based system than a drylot system. Feed costs were five times greater (P<0.01) in the drylot system; increasing total cost per head to over $60.00 for the drylot system verses only $12/ head in the pasture system. Interestingly, pasture calves ex hibited greater (P<0.01) ADG from day 0 to the midpoint of the preconditioning period, suggesting the pasture based system was less stressful as calves had less of an environmental and nutritional adjustment to make immediately following weaning. In a foll ow up study, Mathis et al. (2009) evaluated pasture based preconditioning using a high input and a low input method. Calves allocated to a high input pasture system received ad libitum access to a self fed corn wheat middlings based pellet, while low input calves received a 32% crude protein range cube three times per week. Again, the high input system, although pasture based, resulted in greater (P<0.01) post

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64 weaning gains than the low input system. Low input calves gained 0.50 kg/head/ day on average, whil e h igh input calves gained 0.82 kg/head/ day on average. High input calves also exhibited heavier (P<0.01) body weights at the conclusi on of the preconditioning period, despite similar weaning and trial interim body weights As a result of greater gains an d heavier final body weights, high input calve s in this trial had a $20/ head greater (P<0.01) final value than low input calves. However, greater (P<0.01) feed costs in the high input system resulted in a $20.54/ head net income advantage for low input calv es. These results are in agreement with the previous study conducted by Mathis et al. (2008 ), indicating a lower cost approach may be more profitable post weaning despite greater gains and more marketable calf weight S i milar results were reported by St. L ouis et al. (2003), who evalua ted performance and profitability in nearly 200 purchased heifer calves on drylot or winter annual pasture in Mississippi. Calves were assigned to one of three treatments; calves on drylot receiving 4.54 kg/head/ day of a mixed grain diet, calves on drylot rece iving 2.27 kg/head/ day of a mixed grain diet, or calves on ryegrass pasture receiving no supplementation. At the conclusion of the 21 day preconditioning period, n et returns were greatest for ryegrass calves, at $46.38/hea d, compared to $3.21/head and $18.25/ head for drylot calves receiving a high rate of supplement or a low rate of supplement, respectively. Total preconditioning cost for purchased calves on ry egrass was less than $30/ head, while feed costs alone amounted t o nearl y $30/ head in the high supplemented drylot group In contrast to results previously reported by Mathis et al. (2007) and Mathis et al. (2009) ryegrass calves exhibited greater (P<0.05) ADG than either drylot treatment

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65 group. Ryegrass calves g ained 1.33 kg/ day, while t he drylot calves gained 0.84 kg/day and 0.89 kg/ day for high supplement ed and low supplement ed treatments, respectively The higher rate of gain for pastured calves may be due to forage quality differences between the New Mexico trials using native range and the current study using a winter annual In addition, Mathis et al. (2009) reported declines in forage quality throughout the trial period, while no forage quality decline was reported by St. Louis et al. (2003). St. Louis et al. ( 2003) also reported that ryegrass calves exhibited no sickness or death loss while both drylo t treatments each reported 3.03% morbidity during the preconditioning period. Similarly, Boyles et al. (2007) reported that calv es preconditioned on pasture for 3 0 days had nearly 2.5 times less (P<0.05) feedlot morbidity than calves preconditioned on drylot. Mathis et al. (2008) did not report differences in feedlot morbidity between pastured and drylot preconditioned calves, but did report the drylot precondition ing treatment had more (P=0.02) calves die during finishing than the pastured preconditioning treatment Drylot precon ditioned calves exhibited a 7.6% death loss compared to a 0% death loss for pasture preconditioned calves. Although the preconditioning m orbidity rates reported by St. Louis et al. (2003) are relatively low especially for purchased calves, the morbidity and mortality rates reported by St. Louis et al. (2003) Mathis et al. (2009), and Boyles et al. (2007) all indicate pa sture based systems impose less stress on weaned calves Drylot systems force calves to rapidly transition to a dry, unfamiliar diet, which they must eat out of bunks, which they are also not accustomed to. The drylot environment also facilitate s dust and mud accumulation th at may reduce mobility and performance in rainy weather, or irritate

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66 the calf s respiratory tract and increasing the risk of morbidity during dry weather Although data presented would suggest pasture based systems are more profitable due to lower feed cos ts, this may not always be the case. In markets when feed and hay prices are relatively low and premiums for preconditioned calves are such that the value of gain is greater than the cost of gain, drylot based programs may be profitable as well. The decisi on to precondition as well as the method utilized should be made each year using forecasts for calf, feed, and fertilizer market prices. Preconditioning t ime p erio d P reconditioning programs vary in length, with most programs last ing between 14 and 45 days and some lasting 60 days or longer (Dhuyvetter, 2003) Recent data suggest when the period from weaning to feedlot arrival is lengthened beyond 45 days feedlot morbidity and health costs are reduced (Mathis, 2009). L iterature would also suggest that it ty pically takes at least two weeks for calves to regain weight lost during the weaning process ( Cole and McCollum, 2007 ; Alkire and Thrift, 2005 ), making it difficult for producers to recoup expenses through added weight gain when preconditioning periods are only two to three wee ks in length. At the same time, the risk and costs associated with preconditioning tend to increase as the interval from weaning to feedlot entry is lengthened This makes many cow calf producers hesitant to implement programs for lon g lengths of time especially when feed cost are expected to be high. Such a discrepancy creates a challenge for cow calf producers as they attempt to optimize both profitability and calf performance when deciding how long to precondition Data comparing r eturns from various preconditioning periods is limited. Donnell et

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67 Foundation preconditioning sales, reporting net margin s increased approximately $1/ head for each additional day c alves remained in a preconditioning program. This is most likely due to increases in gain above and beyond weaning weight that were achieved through the longer preconditioning periods some producers opted to implement Feed costs and their influence on mar gins were also analyzed. Feed was the largest expense to cooperating producers, equating to approximately two thirds of total preconditioning costs in 2004 and 2005. For every $1 increase in feed and mineral costs net margins were reduced by n early $1.50/ h e ad. Although net returns for the different preconditioning periods were not reported separately, returns for longer preconditioning periods may not have been greater than returns for shorter preconditioning periods since feed costs typically increase with e ach additional day supplement, mineral, and hay is offered In a University of Tennessee study reported by Rawls (2010), preconditioning returns for 45 day and 60 day programs were compared us ing historical data fr om 1995 through 2008. G ross margins bet ween the calf value at weaning and the calf value after preconditioning were estimated for both spring and fall calving seasons. Additionally, i t was assumed calves preconditi oned for 45 days gained 0.80 kg/ day, while calves preconditioned for 60 days gain ed more rapidly at 0.91 kg/ day. Feed costs were estimated and adjusted each year for calves receiving a precondi tioning supplement at 2% of bodyweight. P reconditioned calves were also assumed to have a 1% death loss du ring the preconditioning period and a $0.088/ kg premium at sale Under these assumptions, 60 day preconditioning periods were reported to be more profitable than 45 day preconditioning periods for both fall born and spring born

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68 calves. This is not surprising since calves in the 60 day program s benefited from a longer feeding period and an assumed higher rate of gain per day than calves in the 45 day programs. Although feed costs would have been greater for the 60 day programs, total costs were sprea d out over an additional 15 days and 41 pound s of gain. More importantly, net returns for both 45 day and 60 day programs, regardless of calving season calf sex, weight, or month marketed, ranged from a $25/head profit to a $25/ head loss in at least half to three quarters of the years reported. This suggests preconditioning margins have historically been small regardless of time period implemented. Similar results were reported by Waggoner et al. (2005) using New Mexico Ranch to Rail data. Calves were grouped into four treatments based on preconditio ning period, including 0 to 20 days, 21 to 40 days, 41 to 60 days and greater than 61 days. Although net returns were calculated for the feeding and finishing period only net income increased (P=0.09) as preconditioning period increased. Calves preconditi oned for 0 to 20 days had a net income of $41.66/ head, while calves preconditioned for 40 to 60 days and greater than 61 days had a net income of $2.23/ head and $4.00/ head, respectively. Cost of gain was also highest for calves preconditioned for 0 to 20 days, while calves preconditioned for 41 to 60 days spent the fewest days on feed and had the lowest total feed cost. Although this study did not specifically evaluate preconditioning return s these results are relevant to cow calf producers retaining owne rship through the feedlot segment. Producers opting to retain ownership may capture much more value through the preconditioning process than producers who opt to sell at the end of the preconditioning period when returns are marginal.

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69 Literature comparing the profit margins of short and long term preconditioning periods is limited and warrants further research. The length of a particular program influences both calf performance and costs, which ultimately influence s the cow calf tment. Longer preconditioning periods provide calves with more time to overcome the stress of weaning, adapt to a dry diet, regain weight lost in the weaning process, and gain additional pounds for the producer to market. On the other hand, longer precondi tioning periods also require more resources, specifically in the form of feed, labor and infrastructure which could reduce profitability Nutritional s upplementation and r ate of g ain Costs associated with nutrition constitute the greatest single proport ion of total preconditioning costs (Cole, 1985; Don nell et al., 2007; Lalman and Smith, 2002 ). As previously outline d pasture based programs tend to have much lower associated nutritional costs than drylot based programs. At the same time, forage quality and/or quantity may be not be sufficient to meet nutritional requirements or facilitate gains to cover the costs of preconditioning in pasture based programs (Cole and McCollum, 2007 ; Lusby, 2006 ; Thrift and Thrift, 2011 ) The refore, provision of supplemen tal feeds may be justified to increase post weaning gains over that of grazing alone S everal stocker calf trials illustrate this concept. Paisley et al. (1998) evaluated post weaning gains of stocker calves grazing winter wheat pasture, either receiving s upplementation or not receiving supplementation. Supplement consisting of ground milo, wheat middlings, and an ionophore, was provided every other day in pellet form Unsupplemented calves received free choice access to a high calcium mineral supplement t hroughout the trial period. C alves receiving alternate day energy supplement ation achieve d significantly higher gains than those not receiving

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70 supplementation Over the 127 day trial period c alves receiving supplementation gained 1.33kg/day compared to 1. 15kg/ day for unsupplemented calves resulting in heavier final body weights B iggerstaff et al. (1991 ) also reported increases (P<0.05) in average daily gain when fresh weaned calves received a molasses soybean meal supplement in addition to pasture grazi ng Calves grazed bahiagrass pastures from September to November, which would be the traditional time period for weaning and preconditioning in most cow calf herds (McBride and Mathews, 2011 ) Throughout the three year backgrounding trial, supplementation improved average daily gain by 0.21 kg over that of unsupplemented calves. At the same time, c alf gains across treatments tended to decline during the secon d month of the trial each year. This was followed by an increase in molasses consumption in treatmen t groups where supplement was provided. Decreased calf performance and increased consumption of supplement were most likely due to the seasonal declines in fora ge quantity of bahiagrass pastures during the trial period Similarly, Coffey et al. (2006) eva luated the effect of supplementation and forage source o n the performance of steers in a three year fall backgrounding trial Steers were allowed to graze stockpiled bermudagrass forage or were provided bermudagrass hay as a forage source, while su pplement ed steers received a 14% crude protein supplement at the rate of 1.82 kg/ day. No forage source by supplementation interaction was reported. Although final weight and cumulative average daily gain were similar between the two forage treatments, supplemented steers consistently outperformed unsupplemented steers in each year of the study. On average, supplemented calves

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71 gained 0.34 kg more (P<0.05) per day than the unsupplemented calves over the approximate 80 day trial periods. It is important to note that in each of the trial years, stockpiled forage quantity and quality generally declined from the start of the trial to the conclusion of the trial. Additionally, both forage sources only met maintenance requirements for the steers in the last two thirds of t he trial periods. Reliance on pasture as the sole source of calf nutrition may be a challenge for producers weaning and preconditioning calves in the fall when forage quantity and quality traditionally decline. In such cases, if the costs associated with s upplementation to achieve higher rates of gain are less than the value associated with that gain, supplementation in pasture based systems may prove more economical than grazing alone. When providing supplement, producers should recognize that f resh weane d calves have a distinct need for feed that is bo th high in quality and palatability ( Hersom et al., 2011 ; Lofgreen, 1988; Lusby, 2006 ). Following weaning, calves are stressed, which may alter the ir nutritional status and reduce appetite ( Carroll and Forsb erg, 2007; Hutcheson and Cole, 1986 ) In addition fresh weaned calves spend much of the first few days post weaning bawling and walking the fenceline rather than consuming feed ( Lalman and Smith, 2002 ; Price et. al., 2003 ) As a result, pr econditioning di ets require a higher concentration of nutrients to meet dietary nutritional requirements and need to be palatable to entice consumption of unfamiliar feeds (Cole and McCollum, 2007 ). There are a variety of feeds producers can choose from when preconditioning. C orn, wheat barley, and milo are acceptable feedstuffs because they are energy dense

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72 and have the potential to meet calf nutrient requirements despite limited feed intake ( Addis et al ., 1973 ; Gadberry et al., 2009 ). Provision of high energy supplementation has been shown to increase calf performance post weaning ( Gill et al., 1980 ) but producers should exercise caution when using high energy supplements because they may also increase morbidity rates in stressed calves (Gill et al., 19 80 ). Supplements high in protein, particularly natural sources of protein, may also work well in many preconditioning programs since growing cattle require high quality, readily available protein sources to facilitate growth and muscle deposition ( Hersom e t al., 2011 ) C o product feeds like molasses, citrus pulp, soybean hulls, and dried distillers grains may also be used in growing and preconditioning programs. Co products tend to be affordable alternatives to more traditional sources of energy and protei n like corn and soybeans especially when cow calf producers are located in close proximity to manufacturing sources Several studies have evaluated the use of co products in preconditioning and stocker programs. Most studies would suggest that co products can improve calf performance and profitability in post weaning scenarios over that of grazing alone. Alkire and Thrift (2005) evaluated citrus pulp as both an affordable and palatable source of energy during a 42 day pasture preconditioning trial. C itrus pulp is a co product feed readily available to producers located near citrus processing facilities. Although citrus pulp is an excellent source of energy, crude protein concentrations are low. In order to evaluate citrus pulp as an economical alternative to traditional commodity supplements, the authors utilized urea and undegradable intake protein (UIP) as additional sources of protein. Treatments included an unsupplemented control

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73 group and three citrus pulp supplemented groups each rece iving 2.27 kg of supplement/head/ day. Supplemented treatment groups were citrus pulp with no additional protein source, citrus pulp with 0.22 kg added UIP, and citrus pulp with urea. Regardless of supplement treatment, supplemented calves exhibited greater (P<0.01) ADGs t hroughout the trial period compared to unsupplemented calves grazing bahiagrass bermudagrass pasture alone. Calves receiving citrus pulp with added UIP gained the most over the 42 day preconditioning period compared to the remaining citrus pulp treatments. Citrus pulp with added UIP p roduced 42 day gains of 0.43 kg/head/ day, citrus pulp alone p roduced 42 day gains of 0.33 kg/head/ day, and citrus pulp with urea p roduced 42 day gains of 0.24 kg/head/ day. Profitability of supplementation verses grazing alone w as also evaluated by the authors, indicating supplementation of citrus pulp with added UIP was the most profitable treatment while grazing alone was the least profitable treatment. Assuming preconditioning resulted in a premium at the time of sale, provisi on of citrus pulp with added U IP would result in a $30.41/ head p rofit compared to an $18.95/ head profit for unsupplemented control calves. Savell et al. (2007 a ) compared the use of soybean hulls to soybean meal in a preconditioning program. Calves grazing bahiagrass berumdagrass pastures were supplemented with either soybean hulls or soybean meal for a 42 day preconditioning period. Both supplements are a co product of t he soybean oil industry and provide adequate crude protein for growing calves. Soybean h ulls are also a good source of energy and provide a high level of digestible fiber. Treatments of soybean hulls and

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74 soybean meal were designed to be isonitrogenous, providi ng 0.27 kg of crude protein/head/ day. Calves receiving soybean hulls exhibited grea ter (P<0.0001) post weaning gains compared to calves receiving soybean meal. Provision of soybean hulls resulted in a 1 5.82 kg/ head body weight gain for the entire preconditioning period compared to only a 10.14 kg/ head body weight gain for soybean meal su pplemented calves. Differences in gain may be attributed to differences in energy intake between the treatment groups. In order to keep treatments isonitrogenous, soybean hulls were fed at a higher rate than soybean meal resulting in a greater amount of t otal digestible nutrients (TDN) being provided in the soybean hull treatment group. Profitability estimates indicate that feeding soybean hulls can also be more profitable than feeding soybean meal during preconditioning. Assuming preconditioned calves rec eived a premium at the time of sale, calves preconditioned with s oybean hulls earned a $7.21/ head profit, while those preconditioned on soybean meal lost $0.41/ head compared to being sold at weaning. Austin and Thrift (2007) evaluated the use of molasses, another by product energy supplement in a pasture based preconditioning program Molasses, an affordable by product of the sugar industry, is an excellent source of energy commonly used to increase weight gain in grazing cattle. Molasses is typically for tified with nitrogen or protein containing products to increase crude protein content, especially when utilized in growing programs (Hersom et al., 2011 ). In the current study, calves were allotted to one of four treatme nts; unsupplemented control, 16% cru de protei n fortified molasses slurry, 16% crude protein fortified molasses slurry with an added b ypass methionine source, and 32% crude protein fortified molasses slurry. The bypass methionine source

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75 treatment was incorporated into the study as an alternat ive to the traditional slurry non protein nitrogen source urea. All treatments grazed b ahiagrass pasture, with liquid molasses supplied ad libitum through lick tanks. Molasses supplementation increa sed (P<0.05) average daily gain over that of unsup plemente d controls during the 42 day preconditioning period. Unsupplemented calves lost weight throughout the trial period, exhibiting an ave rage daily gain of 0.06 kg/head/ d ay. Calves supplemented with 16% mo lasses slurry gained 0.05 kg/head/ day with no differen ces in daily weight gain exhibited between any of the molasses supplementation treatments. Although supplemented calves gained slightly more than unsupplemented controls, weight gains throughout the trial period for all treatments were insufficient to cove r the costs of preconditioning when preconditioning failed to bring a management premium for calves. Poor calf performance in the supplemented treatments may be a result of the nitrogen and protein sources used in the trial. Natural protein sources are oft en better utilized by growing cattle than synthetic or non protein nitrogen sources (Hersom et al., 2011 ), which were used exclusively in this study. Results of this study and others (Savell et al., 2007b; Thomas et al., 2009; Thrift et al., 2003) illust ra te p reconditioning profitability is dependent on a variety of factors, including supplementation source, rate of gain, feed costs and the ability of producers to capture added value through the marketing process. It has been demonstrated that t he provisi on of supplementation can increase preconditioning gain s over that of grazing alone The act of supplementation however, does not definitively produce gains that make supplementation profitable in all cases. In an effort to achieve profitable rates of gai n in grazing cattle many p roducers opt to

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76 utilize feed additive technologies like ionophores and subtherapeutic antibiotics, in conjunction with supplementation. Both ionophores and antibiotics work by manipulating the microbial population within the rum en and intestinal tract, r educing digestive disorders, improving digestion and absorption of feedstuffs and ultimately promoting growth in cattle ( Holdsworth and Parker 2003) Ionophores are classified as an antibiotic because of their bacteriostatic pr operties. Originally used in the poultry industry to control coccidiosis, this class of compounds includes the ionophores monensin lasalocid and laidlomycin proprionate (Bergen and Bates, 1984; Callaway et al., 2003; Schelling, 1984). The specific mode o f action by which ionophores work to improve calf performance is related to the ir ability to modify the flow of ions within the lipid bilayer of bacterial cell walls ( Holdsworth and Parker 2003; Bergen and Bates 1984) T his can disrupt the bacterial orga to regulate metabolic functions as intracellular ATP is lost through degradation in the (Berge n and Bates, 1984 ; Callaway et al., 2003 ) Some ionophores also have the ability to disrupt the sodium ion gradient of speci fic bacterial cells, which can increase intracellular ion concentration and cause bacteria to swell and burst (Bergan and Bates, 1984). As a result, ionophores can selectively inhibit bacteria specifically gram positive bacteria within the digestive tract of ruminants (Fernando et al., 2005) subsequently influencing calf performance Research documenting improvements in calf performance through the inclusion of ionophores in feedlot diets is extensive. When used in conjunction with high starch diets, iono phores reduce feed intake while maintaining gain, ultimately improving feed efficiency during the finishing period ( Horton and Palmer, 1981; Laudert, 1997 ). When

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77 used in grazing cattle, i onophores have been shown to elicit a gain response in some studies ( Horton et al., 1992; Paisely et al., 1998; Worrell et al., 1990 ) while in others gain was not influenced or reduced ( Montgomery et al., 2000 ). Differences in performance responses may be dependent on several factors, including forage quality, forage quant ity, environmental conditions as well as ionophore supplementation rate and frequency (Bretschneider et al., 2008; Horton et al., 1992). Inconsistencies in grazing cattle responses were reported by Biggerstaff et al. (1991) i n a three year fall background ing trial. Monensin was added to a soybean meal supplement at the ra te of 200 mg/head/ day in the last two years of the trial Heifers grazing bahiagrass pastures in the second year of the trial and receiving a soybean meal monensin supplement g ained 0.11 k g more per head per day over that of heifers receiving a soybean meal supplement without monensin. Monensin suppleme nted heifers gained 0.82 kg/head/ day over the 47 day trial, while non monensin suppleme nted heifers gained 0.70 kg/head/ day. In contrast, g a in response to the addition of monensin in the last year of the trial was reversed. Heifers receiving the soybean meal monensin supplement lost weight over the 55 day trial period while heifers receiving the soybean meal supplement without monensin gained weight. Monensin s upplemented heifers gained 0.07 kg/head/ day while non monensin suppleme nted heifers gained 0.10 kg/head/ day. Supplement consumption between treatments in both years of the trial were similar as was residual forage remaining in pastures a t the conclusion of each year. Additionally, gains of unsupplemented controls were negative in the third year of the trial when monensin response was poor while gains of unsupplemented calves in the second year

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78 were similar to gains of calves supplemented without monensin. This indicates differences forage quality between trial years may have be en responsible for inconsistencies in response to monensin Kunkle and Bates (1989) measured the performance response of grazing Brangus steers and heifers to lysoc ellin supplementation following weaning. Steer and heifer calves were blocked into a heavy and light weight block. Treatments included soybe an meal supplemented at 0.45 kg/head/ day with three levels of ionophore included in th e diet at 0, 50, 100, or 200 m g/head/ day. A n unsupplemented control was also included w h ere calves grazed bahiagrass pasture as their sole source of nutrition for the 91 day trial period Performance response to lysocellin treatment between steers and heifers as well as between light and heavy weight calves was similar throughout the trial period Inclusion of lysocellin in a soybean meal supplement increased (P<0.05) daily gains of grazing calves over that of calves receiving supplement without an ionophore. Shrunk weight gain s were 0. 16, 0.1 5, and 0.13 kg/head/ day for ionophore inclusi on rates of 50, 100, and 200 mg/head/ day, respectively. Calves receiving lysocellin in a soybean meal supplement gained twice as much as unsupplemented controls, exhibiting a 0.66 kg/head/ day rat e of gain compared to a 0.32 kg/head/ day rate of gain for unsupplemented calves. Cost of gain, including protein and ionophore suppl ementation, was less than $0.09/ kg Although this figure would seem to be profitable for the time period, market prices for calves at weaning and following backgrounding were not provided to determine if this cost of gain was less than the value of gain.

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79 Improvements in performance following ionophore supplementation were also reported by Horton et al. (1981). L asalocid was included at 100 mg/head/ day in a supplement offered three times per week during a 140 day winter backgrounding trial. Calves receiving lasalocid supplementation exhibited a 14% improvement in average daily gain, resulting in a 10 kg increase in body weight over that o f calves not receiving the ionophore. Similarly, Pitman and Pa te (1984) reported a 4.7% and 12.3% increase in gain over that of controls in a yearling stocker calf trial for low and high lasalocid intakes, respectively. Steer calves on trial grazed stargra ss pastures for 126 days in the fall with lasalocid provided ad libitum in a mineral mix a t the rate of 0, 216, and 324 g/ ton of mineral mix. Ammerman et al. (1979) evaluated the use of monensin in a 126 day backgrounding program where cottonseed hulls se rved as the major source of dietary roughage. Steers were allotted to one of four treatments; soybean meal without added monensin, soybea n meal with 200 mg monensin/head/ day, soybean meal corn mixture without monensin, or soybean me al corn mixture with 200 mg/head/ day. The authors reported neither monensin nor supplemented energy level influenced average daily gain. Although monensin did not affect rate of gain, it did significantly reduce feed intake in both supplement groups, improving feed conversion by an average of 13 % I mprovements in performance are primarily attributed to one of two things; reductions in rumen degradation of dietary protein and modifications in rumen volatile fatty acid production ( Bergen and Bates, 1984 ; Schelling, 1984). Ionophore s are digestion in the rumen and reach the abomasum where it can be more efficiently utilized

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80 by the animal (Russell and Strobel, 1989; Schelling, 1984). Several studi es have also demonstrated that ionophores reduce the acetate to propionate ratio within the rumen ( Ammerman et al., 1979 ). Propionate production and utilization by the ruminant is considered to be more efficient than the production and utilization of the o ther volatile fatty acids (Call away et al., 2003 ). As propionate production increases, methane production also decreases ( Joyner et al., 1979 ), leading to increased carbon and energy retention during the fermentation process ( Bergen and Bates, 1984; Callaw ay et al., 2003 ). Ionophores can also be used in conj unction with antibiotics in grazing cattle supplements and fe edlot diets during the receiving period. Duff et al. (1995) allotted 250 crossbred calves to four treatments following arrival and processin g at the feedlot. All calves rec eived ad libitum access to a 70% concentrate diet during the 28 day trial period. Treatments included a control diet without ionophore, monensin added at 20 g/ ton and tylosin at 10 g/ ton of dietary dry matter, monensin added at 30 g/ ton and tylosin at 10 g/ ton of dietary dry matter, and lasalocid included at 30 g/ ton and oxytetracycline at 8 g/ ton of dietary dry matter. Rate of gain from day 0 14, 15 28, or 0 28 were not influenced by treatment, indicating ionophore ty pe and level did not affect calf performance during receiving. D aily dry matter intake from day 0 28 tended to be lower for ionophore treatment gro ups compared to control calves; however, feed to gain ratios throughout the trial period were similar among all treatment groups. Although reduced feed intake did not negatively affect average daily gains in this study, it does have the potential to influence calf health and performance if intake is reduced to the point where daily nutrient

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81 requirements are not met. Reduced dry matter intake following ionophore supplementation in stressed calves have been reported by other authors and may be due in part to poor palatability (Addis et al., 197 3 ; Balsi et al., 2010a; Pritchard and Thomson, 1992 ). The addition of d ie tary ionophores and feed grade antibiotics in the receiving ration did reduce the numerical percentage of calves exhibiting coccidial oocysts. Fecal samples obtain ed on day 0 indicated nearly 75% of calves exhibited some degree of coccidiosis before trea tments were initiated. Incidence of coccidial oocysts decreased up to 22.2% across treatments by the conclusion of the trial. Ionophores and antibiotics administered through the feed, like monensin and oxytetracycline, can help producers control diseases l ike coccidiosis, which may improve health and subsequently performance in high risk, recently weaned calves Duff et al. (2000) examined antibiotic regimes while comparing pre shipping and arrival medication in feedlot calves during the receiving period. T wo studies were conducted using medium weight steers and light weight steers and bulls. Medium weight steers were assigned to either a control treatment not receiving antibiotic medication, a pre shipping treatment receiving an injectable antibiotic (tilmi cosin phosphate) prior to arrival at the feedlot, and an arrival treatment receiving the same injectable antibiotic after arriving at the feedlot. Light weight bulls were castrated and both steers and castrated bulls were allotted to a control, pre shippin g, or arrival treatment as in experiment one. Light weight c alves in experiment two were then assigned in a 3 x 2 factorial design to either receive feed grade chlortetracycline or not receive feed grade chlortetracycline from day 5 through day 28 of the r eceiving phase.

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82 In experiment one, a verage daily gain, daily dry matter intake, or feed efficiency were similar for control and trea ted calves regardless of whether antibiotics were administered prior to shipment or at arrival at the feedlot Throughout the 35 day receiving period, average daily gains were 1.18 1.24, and 1.27 kg/head/ day for control, pre shipping, and arrival treatments, respectively. Similarly, pre shipping or arrival antibiotic treatment with injectable tilmicosin phosphate did not sig nificantly improve rate of gain, intake, or feed efficiency in calves from day 0 day 28 of the trial period in experiment two. A n interaction between tilmicosin phosphate and chlortetracycline was observed from day 5 day 10 in light weight calves duri ng experiment two Control calves not receiving tilmicosin phosphate either pre shipping or at arrival made a greater (P<0.10) improvement in average daily gain when chlortetracycline was added to the diet on day 5 than calves receiving tilmico s in phosphat e before or at arrival. C alves receiving chlortetracycline in the diet gained 0.05 kg/head/ day from day 5 day 10 while control calves not receiving chlo rtetracycline in the diet lost 0.32 kg/head/ day during this interval. Additionally, gain to feed rati o was increased (P<0.10) with the addition of chlortetracycline in the diet during day 0 day 14 of the 28 day receiving period. Although performance response was inconsistent between trials, morbidity rates in medium weight and light weight calves were greater (P=0.01) for control calves than the medicated treatment groups in both trials. In experiment one, nearly 72% of control calves had to be treated for BRD, while only 46% of calves receiving antibiotic medication required t reatment. In experiment tw o, 40% of control calves required treatment, while 18.7% of pre shi pment calves and 7.5% of arrival calves required

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83 treatment. Morbidity rates were similar between light weight calves receiving chlortetracycline in the diet and those not receiving chlortet racycline in the diet. Similarities in BRD morbidity rate between feed grade antibiotic administration treatment groups may be due to differences in intake of individual animals. Although pen intakes were similar between these treatments during the receivi ng phase, sick and/or stressed animals susceptible to disease may not have consumed enough chlortetracycline to reduce overall treatment group morbidity. Brazle (1994) measured the effect of chlortetracycline within a mineral mixture for stocker cattle gr azing native grass in Kansas. Steers were provided ad libitum access to mineral mixes with four levels of chlortetracycl ine; 0, 150, 300, or 450 mg/head/ day. Supplementation of chlortetracycline did not elicit a gain response in calves during the 92 day tr ial period. Control calves provided with mineral but no chlort etracycline gained 1.168 kg/head/ day. Calves supplemented with 150, 300, and 450 mg of chlortetracycline/head/ day gaine d 1.172, 1.168, and 1.172 kg/head/ day, respectively. Incidences of footrot and eye problems were similar between controls and all treatment levels of added chlo rtetracycline. Only 2% of controls exhibited footrot and less than 7% of controls exhibited eye problems, indicating overall morbidity in this group of stocker calves was low and may not accurately assess the efficacy of feed grade chlortetracycline in grazing cattle. Hubbell et al. ( 2000) also evaluated the efficacy of chlortetracycline in a three month fall and winter grazing trial. Calves were offered 0.91 kg of corn/hea d/ day to act as a carrier for one of two antibiotic feed additives evaluated in the trial. Treatments included a control with corn and no feed grade antibiotic, corn with 70 mg/animal/ day of

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84 chlortetracycline, an d corn with 20 mg/animal/ day of bambermycin. Measures of gain reported by the authors indicate supplementation with a feed grade antibiotic while grazing endophyte infected fescue does not provide a significant growth advantage over that of corn supplementation alone. Control steers gained 56.36 kg over the entire trial period, while steers fed chlortetracycline gained 67.73 kg and steers fed bambermycin gained 59.55 kg. Prior to treatment assignment, calves were preconditioned for 30 days. Although morbidity rates were not reported, p reconditioning may have improved calf health and nutritional status prior to the initiation of the trial, subsequently influenc ing calf response to the provision of antibiotics. In contrast, Erwin et al. (1956) reported significant increases in gain when chlortetracyclin e was added to alfalfa or wheat straw rations in a small scale study. Yearling steers were allotted to treatment in a 2 x 4 factorial experiment, with roughage source (alfalfa and wheat straw), chlortetracycline, fat, and stilbestrol level as variables. No interactions between chlortetracycline administration and the other variables were reported. When chlortetracycline wa s added in the diet at 5 mg/ 0.45 kg for both roughage rations, gain increased by 0.1 kg/head/day and by 0.14 kg/head/ day for the alfalfa and wheat straw rations, respectively. Chlortetracycline administration did not influence feed intake or feed efficiency over the 183 day trial period. Addis et al. (1973 ) also reported positive performance responses to dietary antibiotic supplementation in three separate trials. The feed grade antibiotics Aureo S 700 (chlortetracycline sulfamethazine) and B acitracin MD were added to a 72% concentrate feedlot receiving ration. Calves allotted to the Aureo S 700 treatment received the antibiotic at the rate of 700 mL daily for the first 28 days following arrival.

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85 Bacitracin MD calves received the antibiotic twice daily for the first days of each 28 day feeding period. Control calves offered the receiving ration without a feed grade antibiotic ate more during the first two weeks of each trial than calves offered rations with Aureo S 700 and Bacitracin MD. Although initial gains favored control calves, average daily gain over the entire 56 day trial periods were higher for calves receiving feed grade antibioti cs. In the third trial, control calves exhibited an a verage daily gain of 1.27 kg/head/ day, while Aureo S 700 calve s exhibited gains of 1.32 kg/head/ day and Bacitracin MD ca lves exhibited gains of 1.37 kg/head/ day. Feed conversion was highest for control c alves compared to calves being supplemented with an antibiotic. Improved feed efficiency for antibiotic treated calves resulted in lower costs of gain than control calves despite higher treatment and processing costs for antibiotic fed calves. Although va riable, literature on feed grade antibiotic s and ionophore s indicate health and performance of stressed calves can be improved with supplementation. Responses in daily gain, intake, and feed efficiency result in widespread use of these feed additives in th e feedlot segment ( USDA APHIS, 2011; USDA NAHMS, 1999 ). Their success in receiving and finishing diets have expand ed their use in post weaning scenarios in the stocker, backgrounding and cow calf segments ( USDA NAHMS, 2007 ). At the same time, consumers ha ve become increasingly concerned about subtherapeutic antibiotic usage in food animal production and their role in antibiotic resistance in humans. This has prompted researchers and producers to seek alternatives to feed grade antibiotics and ionophores in diets of calves at the highest

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8 6 risk of becoming morbid Alternatives for use in ruminant diets include probiotics and yeast based additives The use of these products in both monogastric species and pre ruminants as non antibiotic feed technologies indica te they have the potential to elicit improvements in health and performance in young, stressed calves. Hulut and Cravener (2011) reported similar feed conversion ratios, body weights, and mortality rates among turkey hens fed a commercial control diet cont aining either feed grade antibiotics or a yeast based additive. Bertrand and Martineau (2009) incorporated a yeast based additive into the diet of veal calves, reporting performance improvements that extended into the fattening period. Similarly, Kerr et a l. (2007) reported the addition of a yeast based additive to milk replacer significantly improved average daily gain and total weight gain in dairy calves. Newman et al. (1993) reported significant improvements in average daily gain when a yeast based add itive was added to milk replacer in dairy calves. Mannan oligosaccharide offered through non acidified milk replacer improved average daily gain by 4.227 kg/ day over that of controls receiving an unsupplemented milk replacer. A starter diet was also offere d to calves ad libitum in both treatment groups, of which in take was increased by 18% in the mannan oligosaccharide treatment group. Incidence of respiratory disease decreased with mannan oligosaccharide supplementation, possibly improving intake and rate of gain in this treatment group. Responses to yeast based additives in ruminant animals have been less consistent in the available literature. Cole et al. (1992) incorporated yeast culture at various levels in the receiving diets of feeder calves and lambs in four different studies.

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87 Yeast culture was added included in the die t at a rate of either 0 or 0.75% in the first and third feeder calf studies, and at a rate of 0, 0.75, 1.125, or 1.5% in the second and fourth feeder calf and lamb studies. Including ye ast culture into feeder calf diets for 57 days did not significantly improve performance during receiving in the first and second studies. Morbidity rates were similar between control and yeast supplemented calves; however, the authors did report an improv ement in response to antibiotic treatment in yeast supplemented calves. In the third study, calves supplemented with yeast culture tended to weigh more and exhibit higher feed intake than controls after an infectious bovine rhinotracheitis virus challenge, indicating the addition of a yeast culture may elicit greater performance responses in sick verses healthy cattle. Phillips et al. (1985) reported similar inconsistencies in response to yeast culture supplementation in feeder calves. Yeast was inc luded in the diet at 0, 1, or 2% of dry matter in the diet. Light weight feeder calves were subjected to weaning, fasting, re feeding, and re fasting to simulate the stress associated with traditional weaning and marketing channels. Although dry matter intake of b oth yeast culture treatment groups tended to be higher than controls, gain response to yeast culture supplementation did not exhibit a clear trend throughout the trial period. Intake for control calves in trial two was 4.1 kg/head/ day, while average dry ma tter intake for yeast supplemented calves was 5.1 kg/head/day. This resulted in a 24% improvement in dry matter intake after yeast culture was added to the diet of stressed calves. Dry matter intakes between yeast treatment groups and controls in the first two weeks of each trial were not extremely depressed despite the fasting conditions simulated in the design of the experiment. This indicates calves may not have been stressed enough to reduce

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88 appetite to the degree observed in other stress calf studies ( Lofgreen et al., 1980; Lofgreen et al., 1981), explaining why gain response to yeast culture was inconsistent and not improved over controls in most cases. Birkelo and Rops (1994; 1995) investigated the effect of yeast culture supplementation in growing ca lves and yearling steers in the feedlot in two separate trials. Weaned calves were blocked by weight and allotted to either a control or yeast supplemented treatment (Birkelo and Rops, 1994). Calves on both treatments were limit fed a high concentrate diet for an average of 99 days. Rate of gain and feed efficiency measures were similar between controls and calves supplemented with a yeast culture product in both heavy weight and light weight blocks. Average daily g ain in controls was 1.09 kg/head/ day while average daily gain in yeast supp lemented calves was 1.05 kg/head/ day. In a follow up study, Birkelo and Rops (1995) evaluated the use of a yeast culture in the finishing diet of yearling steers fed a high concentrate diet. Again, steers were allotted to either a non supplemented control or a yeast supplemented treatment group. No treatment differences were reported for weight gain or feed efficiency during the finishing period. Additionally, hot carcass weight, percent USDA Choice and abscessed livers wer e not influenced by yeast culture supplementation. The authors concluded inclusion of a yeast product in high concentrate diets for growing calves and yearling steers does not benefit health or performance under such experimental conditions. One yeast deri ved product used in food animal diets includes the mannan oligosaccharide Bio Mos. Tassinari et al. (2007 ) used Bio Mos in receiving rations for fresh weaned calves arriving at the feedlot to evaluate its effect on calf health and

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89 performance in a small scale study. Throughout the 48 day receiving trial, half of the calves on trial received a control receiving diet without Bio Mos supplement and the other half of calves on trial were supplemented with the Bio Mos additive. Although dry matter intakes we re similar between treatments, weight g ain was increased by over 3% with Bio Mos supplementation, subsequently improving feed to gain ratios for the Bio Mos treatment group. Additionally, measures of the immune system indicated yeast derived supplementat ion improved calf immune response to vaccines administered upon arrival. Improvements in rate of gain and feed efficiency may be due to reduced stress levels during the transition period between weaning and finishing as indicated by lower globulin, and globulin levels in Bio Mos calves. In a separate trial evaluating Bio Mos in feedlot receiving diets, inclusion of the yeast product yielded similar improvements in calf performance and health (Alltech Technical Update Bio Mos 935 RT, 2 006) Nine hundred and two crossbred weaned calves were allotted randomly to one of two treatments; receiving diet without Bio Mos and receiving diet with Bio Mos. The receiving diet consisted of barley silage, barley, a vitamin mineral premix, and chlor tetracycline. The Bio M os treatment group had 20 g of Bio Mos added to this receiving diet per head per day for the first 20 days following feedlot placement. Average daily gain was improved 0.24 kg/head/ day and feed conversion was improved from 12. 47 in controls to 8.53 in Bio Mos supplemented calves. Approximately 50% of the control calves required tr eatment, while approximately 18% of Bio Mos supplemented calves were pulled and treated for sickness during the trial periods. Treatment costs were redu ced by nearly half, and mortality rate decreased

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90 over 2% between study treatments following Bio Mos administration for 20 days. Improvements in health and performance significantly reduced total feeding costs for calves supplemented with Bio Mos. Total co sts, including feed cost per head (with Bio Mos ), processing, trea tment, and mortality was $62.41/ head for Bio Mos supplemented calves over an average feeding period of 70 days. Total cost for control calves was $106.46/ head over an average feeding perio d of 92 days. Feed and mortality costs made up the largest proportion of total costs since control calves had lower gains, poorer feed conversions, and higher death rates. It should be noted that a true control diet evaluating Bio Mos supplementation as a n alternative to feed grade antibiotics was not included in this trial. Bio Mos was used in conjunction with chlortetrac ycline in the receiving rations, which may influence the efficacy of Bio Mos when offered to fresh weaned calves arriving at the feedl ot Actigen a concentrated form of the yeast derived additive Bio Mos has been evaluated in a limited number of food animal production trials. Literature available on Actigen is primarily restricted to its use in the poultry, swine, and dairy industri es as a feed additive to mitigate production stress in young animals. It is thought Bio Mos and Actigen improve calf performance by regulating the immune response during stress and eliminating harmful bacteria from the intestine (Alltech, unpublished dat a ; Chandler and Newman, 1994 ). Aris et al. ( 2011) used ten Holstein calves fed either a control milk replacer or a milk replacer containing Actigen (1 g/head/ day) to measure inflammatory response associated with Escherichia coli infections. Actigen suppl ementation for 42 days helped to mitigate the immune response in intestinal tissue by downregulating the expression of pro inflammatory cytokines.

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91 Close et al. (2011) reviewed 12 different studies and reported reductions in pre weaning piglet mortality ra tes and increases in piglet birth weight and wean ing weight when sows were fed Actigen in late gestation. The improvements in piglet weights and health were associated with increased quantity and quality of colostrum produced by the sows in the studies. B rennan et al. (2010) reported increases in goblet cell size and small intestinal mucin secretion following Actigen supplementation in broiler chicks. Additionally, Brennan et al. (2010) compared the efficacy of Actigen to the conventional feed grade anti biotic Bacitracin MD when added to a corn soybean broiler diet. Actigen and Bacitracin MD regulated mucin production and immune response in similar fashions within the gut, improving small intestine function over that of the control diet without any feed additive. Unfortunately data utilizing Actigen in ruminants, particularly in beef cattle at or around the time of weaning, is currently unavailable. According to literature published on monogastrics and pre ruminants, Bio Mos and Actigen seem to have so me potential for regulating stress and im proving performance in food animals These yeast derived additives as well as other direct fed microbial alternatives may be utilized in increasing amounts if government regulation and/or consumer demands restrict a ntibiotic use in livestock diets. This creates a clear need to determine the efficacy of feed grade antibiotic alternatives as more consumers become opposed to subtherapeutic antibiotic usage in food animals. Specifically, more research is needed to determ ine the efficacy and cost effectiveness of antibiotic alternatives in conjunction with calf management practices like preconditioning, which have the potential to reduce calf stress and improve performance and value in beef calves.

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92 CHAPTER 3 EFFECT OF T IMING OF CASTRATION ON NUR SING CALF BODYWEIGHT GAIN AND WEANING WEIGHT Story in Brief The objective of this study was to determine if timing of castration in nursing calves affected calf performance, primarily weaning weight. Ninety two calves were assigne d to one of two castration treatments, early (average age at castration 36 + 18 days ) or late (average age at castration 131 + 26 days). Calves were stratified to treatment by birth date, breed (Angus or Brangus), and cow age. All calves were surgically ca strated using a Newberry Knife to incise the scrotum and traction to remove the testes. Birth weight was similar (P > 0.83) between early and late castrates at the onset of the experiment. Actual weaning weight, adjusted 205 d weaning weight, and body weight change throughout the experimental period were all similar (P > 0.51) between early and late castrate treatments. Brangus calves tended (P=0.06) to be heavier at weaning and had heavier (P=0.01) adjusted 205 d weaning weights compa red to Angus calves Howe ver, there was no breed by castration interaction (P > 0.40) between early and late castration treatments for any of the measurement points. This study suggests that delaying castration until calves were more advanced in age was not advantageous to increasin g weaning weight. Rationale Castration is a common management practice within the United States beef industry. Traditionally, steers have held a distinct advantage in the market place over their intact contemporaries because of their ability to fit within modern beef production systems and produce a more desirable carcass for consumers ( Bretschneider 2005). Although intact males will gain more efficiently and produce a higher red meat yield than

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93 steers ( Arthaud et al., 1969), their aggressive behavior an d reduced carcass quality create a need for bull calves to be castrated prior to weaning. Although the practice of castration is widely utilized within the industry the timing and method utilized for castration can vary considerably from operation to ope ration (USDA NAHMS, 2007) Factors that may impact timing of castration include producer philosophy, product marketing claims, weather, and availability of resources such as facilities or labor. Some cattlemen believe that delayed castration can improve gr owth rate in nursing calves. This belief is also endorsed by some product manufacturers who claim that delayed castration can create significant weight gain advantages at weaning compared to calves that were castrated at or near birth. Since producers are paid on a pounds basis and most cattlemen opt to market their calves at weaning, differences in weaning weight can mean differences in profitability. Despite the perceived benefits of delayed castration, studies have shown that both light weight and yearl ing calves castrated post weaning have significantly reduced feedlot performance and health compared to calves that were purchased as steers (Brazle, 1992; Berry et al., 2001; Knight et al., 1999). Additionally, there is evidence that castration elicits a greater stress response in older calves than in calves that were castrated at or near birth (Stafford and Mellor, 2005). As the principles of animal welfare and the economics of efficiency become increasingly more of a focus within the beef industry, produ cers may find that the supposed benefits of delayed castration are far outweighed by its drawbacks. The objective of this study was to determine if age at castration resulted in significant differences in weaning weight and growth rate in nursing calves. In addition,

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94 comparisons between Angus and Brangus calves were made between treatment groups to determine if there was a breed by castration effect. Materials and Methods Ninety two intact Angus and Brangus bull calves were utilized in the study. Calves w ere born between December 18, 2009 and March 28, 2010. Calves were stratified by birth date, breed (Angus or Brangus), and cow age (first time heifer or cow), paired, and then randomly assigned to one of two treatment groups, early (n= 51) or late (n=42) ca stration All calves were surgically castrated using a Newberry Knife to incise the scrotum and traction to remove the testes. Early castrates (n=23 Angus; n=28 Brangus) were 36 days of age on average (range 3 to 73 days of age) at time of castration (Marc h 1, 2010 and April 23, 2010). Late castrates (n=15 Angus; n=26 Brangus) were 131 days of age on average (range 84 to 180 days of age) at time of castration (June 16 and June 17, 2010). At the time of castration, average body weight of the late castrate tr eatment group was 162 + 4.9 kg All calves were weighed once per month beginning in May until weaning o n August 16, 2010 The experiment took place at the University of Florida Boston Farm Santa Fe River Ranch Beef Research Unit. C ow calf pairs had ad libi tum access to hay with co product supplement during the winter months ( December 2009 through April 2010 ), and were maintained on bahiagrass ( Paspalum notatum ) pasture throughout the remainder of the trial period. The experiment was designed as a completel y randomized design, with castration treatment, breed, and breed by treatment as the fixed effects, steer within treatment as the random effect and individual calf as the experimental unit. Data were analyzed using the Mixed procedure of SAS v9.2. Means we re calculated using the least squares

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95 means, and means were separated using the P diff option when the overall F value was <0.10. Results and Discussion There was no breed by castration interaction (P > 0.40) between treatments for any of the measurement po ints in this study, which suggests the effect of time at castration was not different for the two breeds utilized. At the initiation of the trial, calf birth weights (Table 3 1) were similar (P=0.83) amon g castration treatments However, Brangus calves ten ded (P=0.07) to be heavier at birth than Angus calves. At the conclusion of the trial, mean weaning weight was 206 + 5.2 kg Although weaning weight was similar (P=0.76) between early and late castrated calves Brangus calves tended (P=0.06) to be 13 kg he avier at weaning than Angus calves. In addition, weight per day of age at weaning and adjusted 205 d weaning weight were similar (P > 0.24) between treatments. Brangus calves had greater (P=0.01) adjusted 205 d weaning weights compared to the Angus calves. Calf body weights for the month of May (Figure 3 1), were similar (P=0.98) between the early and lat e castration treatments This implies calves castrated at or near birth (early) had overcome any growth delays related to castration by the time body weight measurements were initiated. Castration in younger, sexually immature calves seems to elicit less of a stress response than castration in older, heavier calves (Bretschneider, 2005; Stafford and Mellor, 2005) Lyons Johnson (1998) reported that calves cas trated at birth or 33 weeks of age had reduced serum haptoglobin levels compared to calves castrated at 36 weeks of age. Haptoglobin is an acute phase protein produced in response to stress and/or injury, making it a useful measure of stress in animals und ergoing management practices like castration (Baumann and

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96 Gauldie, 1994; Murata, 2007). Stress can decrease health and normal behavi ors, like suckling (Blecha, 2000 ). A decreased stress response to earl y castration could account for bodyweight similaritie s among the treatments in May. Additionally, early castrates did not seem to experience any significant disadvantage in growth due to treatment throughout the trial period. Calf body weight change and mean ADG (Table 3 1) were similar (P > 0.19) during the tria l period These results indicate delaying castration approximately 100 days will not result in a significant weight advantage at weaning compared to calves castrated at or near birth. At the same time, early castration should not result in lighter weig ht calves at weaning, which is of significant concern to producers who choose to market at that time. In a study conducted by Bailey et al (1966), calves castrated at approximately three months of age had similar pre weaning growth rates and weaning weig hts compared to calves left intact until weaning. Bagley et al. (1989) found no differences in pre weaning average daily gains and weaning weight between calves castrated at birth and calves castrated at 4 months of age. Although time at castration in the current study differ s slightly from Bailey et al. (1966) and Bagley et al. ( 1989), our findings are in agreement. In contrast, Marlowe and Gaines (1958) repor ted that castrated males grew 5% slower than bulls during a pre weaning trial period in a purebre d herd This resulted in a 7.3 kg advantage in adjusted 210 day weaning weight for bulls over steers. Similar results were reported by Klosterman et al. (1954) and Cundiff et al. (1966). T hese sex differences may be due to selection bias as calves chosen t o remain int act tended to be larger faster growing calves (Cundiff et al., 1966). Producers opting to retain herd sire

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97 replacements generally choose to castrate calves that exhibit less growth potential from both a genotypic and phenotypic standpoint. Whe n selection bias was controlled for Brinks et al. (1961) and Tanner et al. (1970) reported differences in pre weaning growth rate and ultimate weaning were not significant between intact calves and castrates. D ifferences in pre weaning growth and weaning weight between early and late castrates may be further reduced if producers administer anabolic implants at the time of castration. Marston et al. (2003) reported Angus crossbred calves receiving an implant and castrated early, at approximately three mont hs of age gained similarly to calves cas trated at weaning, at approximately seven months of age. Both late and early castrates receiving an implant gained 1.15 kg/ day during the nursing phase However, calves castrated early without an implant only gained 1.08 kg/day during the nursing phase. Lents et al. (2006) reported also calves castrated and implanted between two and three months of age had similar (P > 0.45) weaning weights compared to calves left intact until weaning. Calves banded and implanted at t wo to three months of age tended (P=0.06) to gain more than intact calves prior to weaning (0.94 kg/d ay versus 0.90 kg/d ay respectively). Heaton et al. (2006) implanted and castrated calves at three different ages; less than 90 days, 225 days ( at weaning) and 380 days of age or greater. Average daily gains during the pre weaning phase of the trial were similar (P > 0.89) among treatment groups Although calves were not implanted in the current study, these results suggest a single implant at the time of cas tration could positively impact rate of gain in nursing calves, and compensate for any castration associated weight loss that may occur in young calves.

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98 Since both early and late castration procedures were performed prior to weaning and the onset of pubert y, results from the current study would seem reasonable. Cattle do not attain puberty, and thus secrete significant amounts of growth promoting testosterone, prior to weaning at 6 9 months of age ( Barber and Almquist, 1975; Bretschneider 2005; Lunstra et al., 1978). According to herd data, calves in this study would not have been expected to reach puberty prior to 9 months of age ( Austin, 2009 ) long after calves in the current study were assigned to treatment and castrated The concept underlying delaye d castration is to leave male calves intact long enough to capture the benefits of endogenously secreted androgens that are known to stimulate growth in animals (Gortsema et al., 1974). However, to capture the full benefit, castration would most likely nee d to be delayed until calves were post pubertal. It is only at this point calves would have the ability to secrete enough endogenous testosterone to create significant differences in weight and growth performance (Knight et al., 1999) The comparable puber tal status of the treatment groups in this study likely contributed to the similar weaning weights and growth measures between the early and late castrates.

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99 Table 3 1. The effect of age at castration on calf growth performance Treatment 1 Item Early Late SE 2 P Value Birth weight, kg 36 37 1.1 0.83 Weaning weight, kg 207 205 5.2 0.76 Weight per day of age, kg 1.1 1.1 0.03 0.24 Ad justed 205 d weaning weight, kg 233 229 4.0 0.51 Body weight change, kg May to June 35 34 2.1 0.79 June to July 39 37 1.6 0.40 July to August 45 44 2.0 0.55 May to August 80 78 2.7 0.49 Birth to Weaning 171 169 4.9 0.71 ADG 3 kg/d May to June 1.05 1.03 0.06 0.79 June to July 0.94 0.89 0.04 0.39 July to August 0.7 5 0.72 0.03 0.54 May to August 0.85 0.83 0.03 0.49 Birth to Weaning 0.91 0.87 0.02 0.19 1 Early Castrated (average age at castration = 36 days) Late Castrated (average age at castration = 131 days) 2 Standard e rror (n=92) 3 Average daily g ain

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100 Figur e 3 1. Effect of castration timing on calf bodyweight in May. P= 0.98.

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101 CHAPTER 4 THE COMPARISON OF FE ED ADDITIVES DURING PRECONDITIONING ON GROWTH AND PERFORMAN CE OF BEEF CALVES Story in Brief The objective of this study was to evaluate the response of weaned calves to different feed additives within a preconditioning supplement. Specifically, alternatives to antibiotics and ionophores were evaluated to determine their effectiveness in improving calf performance and mitigating the stress response observe d during the weaning process. Following stratification by bodyweight, sex, previous castration status, and breed, 160 calves were randomly allotted to one of four treatments (n=40 calves/treatment): 1) control calves (CON) were supplemented without additiv es; 2) Chlortetracycline calves (CTC) were supplemented with added chlortetracycline at 350 g/hd/d; 3) Monensin calves (RUM ) were supplemented with added Rumensin at 175 mg/hd/d; and 4) Actigen calves (ACT) were supplemented with added Actigen at 10 g/hd /d. Calf bodyweight was similar (P=0.16 ) among treatments at the beginning of the trial period. Over the 52 day preconditioning period, ACT resulted in the greatest gain response. Chlortetracycline calves exhibited similar (P=0.35) gains to ACT, which were both greater (P < 0.005) than gains exhibited by RUM. Control calves were similar (P > 0.13) to both medicated treatme nts, but did not gain more (P=0.02) than ACT. Plasma concentrations of haptoglobin and ceruloplasmin were similar (P > 0.70) among treatments; however, a day effect (P < 0.0001) was observed in both acute phase proteins measured. Our results indicate Actigen may improve calf performance as effectively as chlortetracycline during a preconditioning period of this length but neither additive was eff ective at mediating stress post weaning

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102 Rationale In recent years the demand for preconditioned calves by the feedlot segment has increased the willingness of beef cattle producers to implement preconditioning programs. There are a variety of programs pro ducers can choose to implement, which may include pre weaning vaccination, castration, dehorning, or a combination of such procedure s (Pritchard and Mendez, 1990). In addition, the period during which calves are preconditioned may vary in length with some calves being weaned and preconditioned for up to 45 or 60 days prior to marketing ( Dhuyvetter, 2003 ) One of the key factors associated with preconditioning is the n utrition of the fre shly weaned calf (Cole, 1985). Nutritional aspects of preconditioning not only consider nutritional needs of the weaned stressed calf but also include the acclimation of calves to dry feed, feed bunks, and water troughs (Savell, 2008). One of the greatest costs associated with preconditioning programs is the cos t of feed in puts (Cole, 1985). The p rovision of supplemental feeds can increase the cost of preconditioning over grazing alone, but the additional gains associated with supplementation may prove more economical than grazing alone. Supplementation can be a favorable m anagement practice to increase the nutritio nal profile of the weaned calf and reduce the stress associated with the weaning process. Another reason for preconditioning calves is to reduce the inc idence of morbidity in calves observed subsequent to weaning a nd prior to feedlot finishing. The preconditioning period allows calves to overcome the physiological and psychological stresses associated with weaning that may suppress immune function and increase calf su sceptibility to disease (Lalman and Smith, 2002 ) Establishing a good immune response before entering the feedlot has been shown to reduce the incidence of

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103 morbidity by 6% and mortality by 0.7% in the feedlot (McNeill, 2001; Cole, 1985). Preconditioning status is one of the major factors associated wi th premium calf prices (King et al., 2006) primarily due to the improved health status of the calves. The use of feed additives in the preconditioning diet is one means to positively affect the health status of fresh weaned calves during preconditioning. Traditionally, preconditioning diets may contain an antibiotic, ionophore, or both. The use of these feed technologies have previously been demonstrated to increase calf performance through suppression of sub clinical disease and im provement in rumen ferme ntation (Holdsworth and Parker, 2003). However, there ha s been an increase in demand for (Smith, 2005) The use of antibiotics and ionophores is precluded from natural programs, eve n during the preconditioning period. The opportunity to incorporate alternative feed technologi es into preconditioning diets that replace antibiotics and/or ionophores may offer producers more flexibility when marketing weaned calves The objective of th is study was to evaluate the response of weaned calves to different feed additives within a preconditioning supplement Specifically, Actigen an alternative to antibiotic s and ionophore s, which are prohibited from use in naturally raised and organic prog rams, was evaluated to determine its effectiveness in improving calf performance and mitigating the stress response observed during the weaning process. Materials and Methods The experiment was conducted at the University of Florida Santa Fe Beef Research Unit in North Central Florida from August 2010 until October 2010. All

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104 Institutional Animal Care and Use Committee (IACU C ). Animals and Treatments Cow calf pairs were gathered off pasture on the morning of August 16, 2010. Steers (n=80) and heifers (n=80) of Angus and Brangus breeds were separated from their dams and placed into one of four dry lot treatment pens (n=40 calves/pen) at the start of the experiment (d ay 0). Calves remained on the ranch of origin for the duration of the experiment. Calves were born between December 2009 and April 2010. All calves received similar pre weaning management, which included vaccination at approximately 4 to 6 months of age, identification, as well as surgical castration and dehorning when necessary All calves on trial were supplemented with a formulated wheat middlings cottonseed meal based pellet (19 % CP, 76% TDN). Supplement pellets were formulated and manufactured by Lakeland Nutrition Group (Eaton Park, FL, USA). Prior to the start of the experiment, a full bodyweight (BW) was taken on July 28, 2010 and calves were blocked by BW breed type, previous castration status, and sex Calves were then randomly allotted to 1 of 4 treatments (n= 40 calves/treatment): 1) control calves (CON) were supplemented with the formulated basal diet without additives; 2) Chlortetracycline calves (CTC) were supplemented with the control diet plus added chlortetracycline at 350 g/h ea d/d ay ; 3) Monensin calves ( ION) were supplemented with the control diet plus added Rumensin (Elanco, Greenfield, IN, USA) at 175 mg/h ea d/d ay ; and 4) Actigen calves (ACT) were supplemented with the control diet plus added Actigen (Alltech Nicholasville, KY, USA) at 10 g/h ea d/d ay Supplements were offered daily a t a targeted intake of 1.82 kg/h ead /d ay All supplements were

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105 formulated to be isonitrogenous and isoenergetic. Adequate feed bunk space was provided in each dry lot pen and pasture. Calves were held in their dry lot trea tment pens (n=40 calves/pen) for 1 week before being transferred to 1 of 32 1.2 ha pastures (n=5 calves/pasture) for a total of 8 pastures/treatment. During the dry lot phase, calves received ad libitum acce ss to perennial peanut ( Arachis glabrata ) hay. Me an forage available per dry lot pen was estimated at 1573.33 DM kg/ha. Each pasture was composed of a mixture of bahiagrass ( Paspalum notatum ) and bermudagrass ( Cynodon dactylon ). The pastures were previously grazed and fertilized at 60 lb N/acre prior to the initiation of the experiment. The nutritional value of the forage in the pastures for the duration of the experiment was 15 % CP, 33% IVDMD The mean forage available per pen at the start of the experiment was estimated at 463.75 DM kg/ha. All pens had a feed bunk, water er and shade provided. Calves remained in the same pasture from d ay 7 to d ay 52 of the experiment. Nutritional composition of preconditioning supplements, peanut hay, and pastures available to calves throughout the trial are presented in Table 4 1. Feed Sampling Pasture samples were obtained on d ay 4 of the experiment, prior to transferring calves to their treatment pastures on d ay 7 of the experiment. Samples were obtained to estimate forage quantity and quality by hand clipping 3 0.25 m 2 areas and compositing the samples. Pasture samples were dried at 60 o C in forc ed air oven for approximately 96 hours Dried samples were ground to pass through a 1 mm screen in a Wiley mil l (Arthur H. Thomas Company, Philadelphia, PA, USA ). Pasture sample s w ere analyzed for CP organic matter (OM), and in vitro dry matter digestibility (IVDMD) Total nitrogen was determined using macro elemental N analyzer (Elementar, vario

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106 MAX CN, Elementar Americas, Mount Laurel, NJ, USA) and used to determine CP (CP = N x 6.25). In vitro DM digestibility of samples was determined using the ANKOM analyzer ( ANKOM, New Jersey, USA ). Supplement samples were analyzed by the same procedure out lined above for pasture samples Sampling and Analysis Calf BW was obtained on 2 con secutive days at the initiation ( d ay 0 and day 1) and termination (d ay 51 and day 52 ) of the experiment Day 0 was the day of weaning, with d ay 1 considered the first day on the supplement. One half of the calves on trial were utilized for intensive bloo d collection to measure acute protein plasma ( APP ) concentrations. C alves were gathered on day 0, 1, 4 7, 11 and 14 for collection of BW and blood samples for APP analysis Additionally, hip height measurements were taken on day 0 and day 51 of the trial Blood samples were collected via jugular venipuncture into 7.5 mL polypropylene syringes containing 1.6 mg potassium EDTA as an anticoagulant (Monove tte, Sarstedt Inc., Newton, NC). Samples were placed on ice immediately after collection and transported to the lab for further processing. Blood samples wer e centrifuged at 1500 x g for 15 min at 5C to obtain plasma, which was place d in sample vials and stored at 2 0C for subsequent analysis of ceruloplasmin and haptoglobin concentrations Plasma cerulopl asmin oxidase activity was measured in duplicate samples by using the colorimetric procedures described by Demetriou et al. (1974). The intraassay CV of duplicate samples was controlled to values of 10%. Ceruloplasmin concentrations were expressed as milli grams per deciliter, as described by King (1965). Interassay variation of both acute result of a control sample analyzed in duplicate within each individual assay run. When

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107 the interassay CV e xceeded 10%, all samples contained in the individual run with the control sample exceeding the average by the greatest were reanalyzed. This step was 10% (inter assay variation = 5. 3 %; intra assay CV variation = 1.9 %). Plasma haptoglobin concentrations were determined in duplicate samples by measuring haptoglobin hemoglobin complexing by the estimation of differences in peroxidase activity (Makimura and Suzuki, 1982). Results are expressed as arbitrary units resulting from the absorption reading x 100 at 450 nm. For samples with an 10% (inter assy variation = 4.35 %; intra assay CV variation = 2.67 % ) Data were analyzed by the MIXED procedure of SAS 9.2 (SAS Inst. Inc., Cary, NC). The model included the mai n effects of treatment All variabl es quantified by day were analyzed using repeated measures. Least square means are reported with standard errors, means were separated for comparison by PDIFF. All variables with P s differ ences, all variables with P values between 0.05 and 0.10 were reported as tendencies and anything greater than 0.10 was considered non significant. All two way interactions found to b e signi ficant at P< 0.10 for a particular variable were included in the mo del for that variable. Results and Discussion Animal Performance Supplement refusal did not occur throughout the trial indicating supplement intake was adequate and similar between treatm ents Starting, intermittent, and ending c alf

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108 bodyweights (Table 4 2 ) were similar (P>0.15) among feed additive treatments. Although, individual bodyweight measurements were not influenced by feed additive supplementation, differences were observed in bodyweight change (BWC) (Figure 4 1 ) and average daily gain (ADG) (Figur e 4 2 ) during the trial period (P<0.0001) Calves offered supplement with ACT gained more (P < 0.03) total weight over the trial period than RUM and CON calves, and tended (P=0.10) to gain more wei ght than CTC calves Additionally, CTC calves tended (P=0.06) to gaine d more than RUM calves but n ot more (P=0.58) than CON calves Similar differences were observed for ADG over the entire preconditioning period. Calves receiving supplement with ACT exhibited a greater (P<0.02 ) cumulative ADG than RUM and CON tre atment groups Calves receiving supplement with CTC also gained at a faster (P<0.01) rate over the 52 day preconditioning period than RUM supplemented calves. Feed additive response between ACT and CTC was similar (P=0.35 ) with ACT calves gaining 0.48 kg/ head/day and CTC calves gaining 0.42 kg/head/ day. Our results indicate Actigen may improve calf performance as effectively as chlortetracycline during a preconditioning period of this length. Several authors have also reported similar gain responses when either a yeast derived or antibiotic additive is provided within food animal diets Hulut and Cravener (2011) reported similar feed conversion ratios, body weights, and mortality rates among turkey hens fed a commercial control diet containing either fe ed grade antibiotics or Actigen Birkelo and Rops (1994) investigated the effect of yeast culture supplementation in growing calves in two separate trials. Weaned calves on both a control and yeast

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109 additive treatment were limit fed a high concentrate diet for an average of 99 days. Rate of gain and feed efficiency measures were similar between controls and calves supplemented with a yeast culture product in both heavy weight and light weight blocks. Average daily g ain in controls was 1.09 kg/head/ day while ADG in yeast supplemented calves was 1.05 kg/head/ day. Y east based additives have also been shown to elicit performance responses over that of food animals not receiving a feed additive. Tassinari et al. (2007) used Bio Mos, which Actigen is derived fro m, in receiving rations for fresh weaned calves arriving at the fee dlot. Although dry matter intakes were similar between treatments, weight gain was increased by over 3% from Bio Mos supplementation, subsequently improving feed to gain ratios for the Bio Mos treatment group. In contrast Vendramini and Arthington (2007) reported no benefit to adding a yeast fermentation product to a concentrate supplement for early weaned calves grazing pasture. The authors reported similar performance responses during th e post weaning grazing period for both treatment groups. Calf gain during winter grazing of ryegra ss pasture was 0.88 and 0.83 kg/head/ day for control and yeast supplemented calves, respectively. Differences in gain response between Vendramini and Arthing ton (2007) and the current study could be attributed to pasture quality, season, and calf age. Early weaned c alves were weaned at an average age of 66 days weighing approximately 84 kg eac h while calves in the current study were weaned at an average age o f 194 days weighing approximately 203 kg each. At only 2 months of age, the rumen and microbial population with in the digestive tract of early weaned calves may not be functioning

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110 enough to respond to a yeast based additive. Additionally, in the winter cal ves grazed ryegrass pasture and in the spring grazed stargrass pastures, which are typically higher quality forage species than the bahiagrass and bermudagrass species the calves in the current study grazed in the fall when forage quality of these species would typically decline. All treatment groups lost w eight following weaning (P=0.73 ), and g ains made duri ng the drylot period (Figure 4 3 ) indicate weight lost as a result of the weaning process was not fully recovered by d ay 7 in all treatment groups. Cal ves offered supplement with ACT and RUM lost 0.08 and 0.41 kg/head/ day respectively, under drylot conditions. Alkire and Thrift (2005 ) and Austin and Thrift (2007) report similar reducti ons in body weight the first week post weaning. Data indicates inclus ion of ionophores in young, stressed calf diets may reduce feed intake and decrease gain if only fed for brief time periods (Ammerman et al. 1979 ; Schelling, 1984 ) Although orts were not collected for any of the treatment pens throughout the trial, RUM ca lves did ex hibit poor performance gains, particularly early in the trial period. The loss in weight for RUM calves could have been due to reduced digestibility as calves adapted to the ionophore. Ionophores can alter the micro flora within the digestive tr act and if calves are not given sufficient time to adapt to ionophore supplementation, digestibility and gain can be reduced initially (Bergen and Bates, 1984; Calloway et al., 2003; Schelling, 1984). Once calves become adapted and the microflora in the r umen and small intestine stabilize digestibility and gain can increase (Bergan and Bates, 1984; Schelling, 1984). Poos et

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111 al. (1979) report ed improvements in digestibility an d performance following a 21 and 28 day a daption period. Losses in gain and body weight in ACT calves during drylot were not as severe as losses exhibited in the RUM treatment (P=0.005) However, these losses cannot be attributed to reduce d supplement intake in either the ACT or RUM treatment group s sinc e supplement consumption me t des ired levels and weigh back was never collected during the drylot period. This indicates that feeding ionophores and yeast derived additives in conjunction with the stress of weaning, adaptation to a dry diet and a drylot environment may not always elicit positive gains or changes in bodyweight in brief post weaning scenarios In contrast to overall measures of BWC and ADG, d rylot gains for calves offered supplement with the feed grade antibiotic CTC were greater (P<0.0001) than the RUM and ACT additive tre atments Chlortetracy cline improved gain nearly 2 kg/head/ day over that of RUM, and by nearly 0.75 kg/head/ day compared to ACT Inclusion of CTC in the diet tended to increase (P=0.07) gain over that of CON calf gains Although overall performance response s were similar between ACT and CTC treatment, it appears offering CTC at a subtherapeutic rate in a preconditioning supplement may be more effective at improving calf performance under drylot conditions immediately following weaning Duff et al. (2000) re ported improvements in drylot gain during the initial weigh periods of a feedlot receiving trial. Calves receiving chlortetracycline in the diet gained 0.05 kg/head/ day from day 5 day 10, while control calves not receiving chlortetrac ycline in the diet l ost 0.32 kg/head/ day during this interval. Additionally, gain

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112 to feed ratio was increased with the addition of chlortetracycline in the diet during day 0 day 14 of the 28 day receiving period. Results of Duff et al. (2000) and the current study conflict with those reported by Addis et al. (1973 ). Calves offered supplement with a chlortetracycline sulfamthazine antibiotic had reduced gains in the initial week of a feedlot receiving study compared to calves receiving the high concentrate supplement without an antibiotic. Compared to control calves, antibiotic supplemented calves gained 0.75 kg/head/ day whil e control calves gained 0.91 kg/head/ day. This is likely due to reduced feed intake of calves receiving the feed grade antibiotic. Controls calves consume d approximately 5% more per day in dry matter than calves receiving the chlortetracycline sulfamthazine additive. Calves exhibiting reduced feed intake post weaning will often fail to consume enough feed to meet their daily nutrient requirements. This can prevent calves from regaining weight rapidly and decelerates gain early in post weaning management systems. In the current experiment, a t the conclusion of the second week, ADG and BWC were positive for all treatments (Figure 4 4 ) and calves continued to gain steadily for the remainder of the pr econditioning period (Figure 4 5 ). This agrees with Cole and McCollum ( 2007 ) who suggest it can take calves between two and three weeks to recover and gain bodyweight post weaning. Our results indicate calve s had a dapted to the supplement offered and overcome the stress of weaning by the d ay 14 of the trial Calves were transitioned to pasture on d ay 7, which may have also aided in calf weight gain during this measurement interval Alkire and Thrift (2005) and Aust in and Thrift (2007) reported positive calf gains following transition from a drylot to a pasture during preconditioning. Drylot preconditioning environments are considered to be more

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113 stressful during the post weaning period than pasture environments (Math is et al. 2008). Placement on pasture during the second week of the current study may have reduced stress while offering calves a more familiar nutrition source than hay offered during the drylot period eliciting positive gain s Performance response to p reconditioning and feed additive supplementation during the pasture period (Figure 4 6 ) indicates ACT calves gained more (P<0.01) weight than CON and RUM calves Bodyweight change in response to ACT supplementation increased 25.45 kg/ head on average during the pasture period, while CON calves gained 15.09 kg/ head and RUM calves gained 14.74 kg/ head on average. Actigen supplementation also tended (P=0.07) to increase bodyweight during this measurement period over that of CTC supplementation. Data examining the use of Actigen in growing cattle under grazing conditions is currently unavailable and the use of similar yeast base d additives in grazing calves is limited in scope. Results reported by Verdramini and Arthington (2007) suggest yeast supplementation during grazing is equally as effective as supplementation without a feed additive. In this study, calves were grazing high quality ryegrass and stargrass following early weaning, while calves in the current study were older and grazing low quality pasture s during the fall of the year when forage quantity and quality traditionally decline. Our results indicate ACT may elicit a greater response than supplement alone in a grazing system when pasture quality is low and calves are older. Pasture quality and io nophore supplementation rate may have also allowed ACT supplemented calves to outperform RUM calves since other authors have suggested ionophore response is

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114 dependent on these factors (Bretschneider et al., 2008; Horton et al., 1992). Additionally, our res ults indicate ACT may work as effectively as CTC and other subtherapeutic antibiotics in pasture based preconditioning programs. Animal Stress Treatment differences in plasma concentration of haptoglobin and ceruloplasmin were not observed throughout the sampling period. However, m easures of both APPs indicate all calves experienced stress as a result of the weaning process. Both plasma haptoglobin (Figure 4 7 ) and ceruloplasmin (4 8 ) concentrations significantly increased from weaning to d ay 4 (P<0.0001) regardless of treatment Both Arthington et al. (2008) and Campistol (2010) reported similar post weaning increases in plasma concentrations of haptoglobin and ceruloplasmin across treatment groups Our results suggest weaning is a stressful management pra ctice for beef calves since plasma concentrations of haptoglobin are often detectable only in cattle undergoing stress (Arthington et al., 2003; Makimura and Suzuki, 1982). Plasma haptoglobin levels at weaning (d ay 0) for a ll calves averaged 6.01 units Pl asma haptoglobin levels peak ed on d ay 4, averaging 7.57 units across all treatments. Plasma concentration of ceruloplasmin exhibited a similar trend post weaning, peaking on d ay 7 and then steadily declining through d ay 14 of the preconditioning period. Al though haptoglobin levels trended downward between d ay 4 and d ay 14, the inflammatory response to weaning was not fully mitigated when blood serum collections ceased on d ay 14. Day 14 haptoglobin levels remained elevated (P<0.0001) from d ay 0 levels, but w ere not different (P>0.59) than levels on day 7 or day 11 Vendramini and Arthington (2007) reported similar differences in peak sampling day and plasma concentration declines between haptoglobin and ceruloplasmin.

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115 No treatment by day interaction was obser ved for haptoglobin concentrations during the sampling period; however, an interaction (P=0.01) between treatme nt and day was detected for ceruloplasmin post weaning (Figure 4 9 ) Despite the interaction, no clear trend in treatment effect was observed for any of the sampling days used to measure stress. Differences between treatments on d ay 0 we re numerically greatest (P>0.07 ) between the ACT and CTC calves (2.61 mg/100 mL + 1.41). Actigen and CTC continued to exhibit the largest numerical (P>0.16) d iffer ences between treatments when plasma concentrations peaked on d ay 7 (1.98 mg/100 mL + 1.41). By the conclusion of the measurement period, differences in ACT and CTC calves on d ay 14 were reduced to 0.61 mg/100 mL + 1.41 which was less than the difference s observed be tween ACT and RUM calves (0.91 mg/100 mL + 1.41) and ACT and CON calves (0.98 mg/100 mL + 1.41) on d ay 14. The interactions detected may be statistically significant, but do not conclusively provide insight into how these feed additives mitiga te stress and influence performance of preconditioned calves. Others have concluded that such interactions are a consequence of the magnitude and time of increase in acute phase concentrations post weaning rather than individual treatment differences with i n sampling day (Arthington et al., 2003). The lack of a relationship between plasma acute phase protein concentra tions and ADG (P>0.23 ) as well as the lack of morbidity and mortality over the trial period suggests none of the feed additives were more or le ss effective at mitigating stress over that of supplementation alone when calf health was excellent and post weaning performance was marginal.

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116 Economic Evaluation A summary of the costs associated with supplementing calves in this preconditio ning trial is given in Table 4 3 Supplement cost differed between treatments, with ACT being the most expensive ($38.87/head) and CON being the least expensive ($35.88) However, i ncremental costs of all additives used were minimal and not a significant (P=0.19) compon ent of feed cost. Although total preconditioning costs were not included in this economic evaluation, profitability of the different preconditioning treatments was calculated by comparing the calves receiving a supplemental feed additive (ACT, CTC, RUM) to calves not receiving a supplemental feed additive (CON) Profit (or loss) was calculated for each treatment by subtracting the feed cost of gain from the value of gain obtained during the 52 day preconditioning period, and then multiplying by the total we ight gained during preconditioning Assuming preconditioned calves would sell for the same price as non preconditioned calves, value of gain obtained during the preconditioning period was calculated to be $1.71/kg/head. In this evaluation, ACT was the onl y profitable treatment ($3.74/head), with all other treatments resulting in losses following the preconditioning period. Actigen supplementation was $20.47/head more (P=0.002) profitable than RUM and tended (P=0.09) to be $10.71 /head more profitable than CON. At the same time, ACT profitability was similar (P=0.20) to CTC, suggesting it may be both an effective and affordable alternative to antibiotic feed additive supplementation when preconditioning does not result in a management premium at marketing. R umensin supplementation was the least profitable additive in this evaluation, r esulting in a $16.73/head loss. This loss was approximately $12.50/head more (P=0.05) than the loss associated with including CTC in the preconditioning supplement.

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117 When assum ing a premium of $0.11/kg at the time of sale, which would not be uncommon if calves were marketed through a certified sale, the value of gain was calculated to be $2.81/kg/head. In this evaluation, all treatments except RUM resulted in a profit. Supplemen tation with ACT and CTC resulted in a $31.14/head and $16.53/head profit, respectively. Control calves not receiving a supplemental feed additive produced a profit of $11.62/head while RUM supplementation resulted in a loss of $3.66/head. Again, profitab ility outcomes for ACT and CTC were similar (P=0.16), while ACT was approximately $35/head more (P=0.002) profit able than RUM. This indicates ACT would be equally or more cost effective than feed grade antibiotics and ionophores in a preconditioning progra m of this length. Actigen also tended (P=0.06) to be more profitable than CON, producing approximately $20/head more profit than supplementation alone Chlortetracycline supplementation tended (P=0.06) to be more profitable than supplementation with RUM. C ontrol calves were intermediate (P>0.14) in profitability to calves supplemented with the t raditional antibiotic additives RUM and CTC, indicating producers may not necessarily benefit from the inclusion of these additives at preconditioning when calves a re kept on the ranch of origin and calf health is excellent. Based on the assumptions outlined above, cattle supplemented with Actigen received the largest economic returns; with Rumensin supplementation receiving the lowest, regardless of if a premium w as offered. Although the addition of low levels of feed additive technologies resulted in variable economic returns within this

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118 preconditioning program, ultimately it seems that Actigen is a suitable alternative to antibiotics when the goal is to improve weight gain in a cost effective manner.

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119 Table 4 1 Nutritive value of preconditioning supplement, pasture, and peanut hay (PHAY) offered to calves throughout the experiment. Item C ontrol Actigen Chlortetracycline Rumensin Pasture 1 P HAY DM, % 94.27 94 .29 94.58 94.73 19.94 91.50 CP 2 % 17.84 19.22 18.98 19.82 14.86 9.74 IVDMD, % 58.44 57.59 60.00 60.71 33.24 36.95 OM, % 90.81 91.18 91.34 91.78 93.39 92.48 1 Mixture of bahiagrass and bermudagrass forage collected at the initiation of the experiment. 2 CP, IVDMD, and OM are expressed on a dry matter basis

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120 Table 4 2 The effect of supplemental feed additive treatment on calf growth during preconditioning Treatment 1 Item CON ACT CTC RUM SE 2 P Value Starting weight (d ay 0) 3 kg 204.4 203.9 198.5 205 .9 2.34 0.16 Ending weight (d ay 52) 4 kg 221.3 228.8 217.3 217.7 3.96 0.17 Body weight change, kg Day 0 to d ay 7 5 1.818 a 0.540 b 2.443 a 2.869 c 0.63 <0.001 Day 0 to d ay 14 5.057 a 6.165 a 3.963 a 0.881 b 1.07 0.01 Day 7 to d ay 14 3.239 a 6.705 b 1.520 a 3.750 a 1.00 0.01 Day 7 to d ay 52 6 15.09 a 25.45 b 16.45 a 14.74 a 2.67 0.03 Day 14 to d ay 52 11.85 a 18.75 b 14.93 ab 10.99 a 2.28 0.09 Day 0 to d ay 52 17.05 ac 25.11 b 19.03 ab 11.99 c 2.53 0.01 ADG 7 kg/d Day 0 to d ay 7 0.260 a 0.077 b 0.467 a 0.410 c 0.0 8 <0.001 Day 0 to d ay 14 0.361 a 0.440 a 0.283 a 0.063 b 0.08 0.01 Day 7 to d ay 14 0.463 a 0.958 b 0.217 a 0.536 a 0.14 0.01 Day 7 to d ay 52 0.335 a 0.566 b 0.411 a 0.328 a 0.06 0.02 Day 14 to d ay 52 0.312 a 0.493 b 0.432 ab 0.289 ab 0.06 0.05 Day 0 to d ay 52 0.325 ac 0.479 b 0.419 ab 0.228 c 0.10 0.002 ab LS means within a row with different superscripts are different P<0.05. 1 CON (control, supplement without feed additives) ACT (supplement with Actigen at 10 g/hd/d) CTC (supplement with chlortetracycline at 350 g/hd/ d) RUM (supplement with monensin at 175 mg/hd/d) 2 Standard e rror (n=32) 3 Starting weight (day 0) was taken by averaging day 0 and day 1 body weight measurements 4 Ending weight (day 52) was taken by averaging day 51 and day 52 body weight measurements 5 Day 0 to d ay 7 drylot period 6 Day 7 to d ay 52 pasture period 7 Average daily g ain

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121 Table 4 3 An economic evaluation of supplemental feed additive treatment during preconditioning Treatment 1 Item CON ACT CTC RUM SE 2 P Value Feed cost of gain, $/kg 2. 85 1.61 2.96 4.30 0.85 0.19 Profit ( loss ) with no premium, $/head (6.97) a b 3.74 a (4.25) a (16.73) b 4.34 0.02 Profit (l oss ) with premium 3 $/head 11.62 a b 31.14 a 16.53 a (3.66) b 7.14 0.02 ab LS means within a row with different superscripts are different P <0.05. 1 CON (control, supplement without feed additives) ACT (supplement with Actigen at 10 g/hd/d) CTC (supplemen t with chlortetracycline at 350 g/hd/d) RUM (supplement with monensin at 175 mg/hd/d) 2 Standard e rror (n=32) 3 Premium of $0.11/kg of calf b odyweight included in profit (loss) calculation

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122 Figure 4 1 Effect of feed additive treatment on bodyweight change during a 52 day preconditioning program. P=0.01

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123 Figure 4 2 Effect of feed additive treatment on average daily gain during a 52 day p reconditioning period. P=0.002.

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124 Figure 4 3 Effect of feed additive treatment on bodyweight change during a 7 day drylot period of a preconditioning period. P=0.02

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125 Figure 4 4 Effect of feed additive treatment o n 14 day average daily gain during a 5 2 day preconditioning period. P=0.01

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126 Figure 4 5 Effect of feed additive treatment on average daily gain from day 14 through day 52 of a preconditioning program. P=0.06

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127 Figure 4 6 Effect of feed additive treatment on average daily gain during the p asture period of a preconditioning program. P=0.02.

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128 Figure 4 7 Effect of sampling day on plasma concentration of haptoglobin post weaning P <0.0001

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129 Figure 4 8 Effect of sampling day on plasma concentration of ceruloplasmin post weaning. P<0.00 01.

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130 Figure 4 9 Effect of feed additive treatment and sampling day on plasma concentration of ceruloplasmin post weaning. P = 0.01

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131 CHAPTER 5 CONCLUSIONS No differences in early and late castration were observed. Calf performance results from this tri al and others indicate that producers have some degree of flexibility in determining when to implement castration. Castration at or near birth will not have a detrimental effect on calf performance or ultimate weaning weight. Equally important, delayed cas tration will not result in added pounds at weaning. Additionally, the addition of low levels of feed additives technologies resulted in variable post weaning gain responses, similar stress responses to weaning and variable economic returns. These results however, are not definitive and more work is warranted to determine how factors like season, calf age, forage availability, additive inclusion rate, and preconditioning system influence performance response to Actigen and other antibiotic alternatives. Equally important, economic analyses evaluating the cost effectiveness of feed additives in preconditioning programs are almost non existent. There is a clear need to determine not only if performance responses can be elicited through additive provision, b ut if the responses observed improve calf value enough to cover the additional costs associated with supplementation.

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148 BIOGRAPHICAL SKETCH Amie Marie T aylor was born in Alachua, Flo rida to Marie and Scott Taylor. She was raised on a small farm outside of Gainesville, Florida where she was active in both 4 H and FFA since the age of eight. Amie graduated from Santa Fe High School in 2004, and then from the University of Florida with a dual Bachelor of Science degree in Animal Science and Agriculture Education in the spring of 2009. During her undergraduate program, Amie served as a UF College of Agriculture and Life Sciences Ambassador for three years. Prior to graduation in the spring of 2009, Amie also completed an internship teaching high school Agriscience students at Williston H igh School in Williston, Florida. Following graduation, Amie was accepted into a graduate program under the direction of Dr. Todd Thrift and Dr. Matt Hersom. During her graduate program, Amie assisted in teaching 33 sections of undergraduate courses withi n the Animal Sciences department, including Introduction to Animal Science, Cow Calf Management, Farm Animal Reproduction and Endocrinology, and Large Animal Practicum. Amie plans on pursuing a career teaching Agriscience at the secondary or post secondary level.