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1 COMPARISON OF REPRODUCTIVE PERFORMANCE AND COST OF NATURAL SERVICE AND TIMED ARTIFICIAL INSEMINATION IN LACTAT ING DAIRY COWS IN FLORIDA By FBIO SOARES DE LIMA THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009
2 2009 Fbio Soares de Lima
3 To Gaspar and Dolores, my brother and sisters, and God that unconditionally supported me under all circumstances and provided me all the str ength necessary to keep my focus to accomplish my goals and happily conquer this dream
4 ACKNOWLEDGMENTS I would like to thank Dr. Carlos A. Risco, chairman of the supervisory committee, who provided me guidance, encouragement, motivation, ex cellent graduate training, unconditional support and trust. His principles and outstanding h uman being kept me inspired and focused on the accomplishment of this work, without him it wou ld not happen. My appreciation is extended to committee members Dr. William W. Thatcher, who w as actively involved in the design of the experiment, analysis and interpretation of results and elaboration of the manuscript; Dr Jos Eduardo P. Santos, who provided valuable insight in the analysis and interpretation of results as well as and the embellishment of this work; and Dr. Louis Archbald for his input in the design and sharing of expertise in the process of writing this thesis. Also, I want extend a distinctive thanks to Marie-Joelle Thatcher, who provide terrif ic help in computer guidance, laboratory analysis during all phases of this thesis, and Dr. Albert de Vries, who actively elaborated and instructed me in completion of the assessment of th e financial aspects of timed artificial insemination and natural service in lactating dairy cows. Very special thanks to Drs. Donovan and Rae for the outstanding clinical training, expertise shared and for allowing me to pursue this simultaneous master degree with my residence program. They always worked out with me c onditions for the conduction of this research. I would like also to express my gratitude to Drs. Mauricio E. Benzaquen, Beatriz B. Sanz, Jacob Crawford, Pablo Pinedo and Belen Rabagl ino, my fellows residents and graduate student colleagues, for their valuable friendship a nd help during those very early morning and long days to conduct this study. Beyond their scien tific contribution and valuable insight, their companionship will be kept in my memories for the r est of my life.
5 I would like also to thanks Pfizer Animal Health an d Select Sires Inc. for financial support. I would like to particularly thank all people from the crew at Dairy Production System in Branford Florida. They all provided an incredible support during the conduction of the farm work. I extended a special thanks to Alberto, Pepe, Victor, Jaime, Luis, Alex, Mario, Rick, Bob and Skip for their dedicated and support. I would l ike to carry on my appreciation to Mr. David Sumrall and Mike Pedreiro for the use of dairy cows bulls and facilities use and unconditional support during the execution of this project. Particularly I want to extend my thankfulness to Ju liana Campos, Katherine Keathley, Lauren Crescenzi, Stephanie Croyle and Linda Miller that participated very intensively of the routine of this project. In addition, thanks to stu dents of the College of Veterinary Medicine from classes of 2008 and 2009 that during their rotation on FARMS were able to experience and help in the project conduction. Final and special thanks go to my family and Bianca Martins that support me with love and comprehension during this stage of my life and to m y friends in Gainesville and in Brazil.
6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................... ................................................... .........................4 LIST OF TABLES .................................... ................................................... ....................................8 LIST OF FIGURES ................................... ................................................... ...................................9 LIST OF ABBREVIATIONS ............................. ................................................... ........................10 CHAPTERS 1 GENERAL INTRODUCTION ........................ ................................................... ....................13 2 LITERATURE REVIEW ........................... ................................................... .........................16 Reproductive Performance of Lactating Dairy Cows .. ................................................... ........16 Estrous Cycle of Dairy Cattle ..................... ................................................... .........................18 Period, Stages and Classifications of the Estrous C ycle .............................................. ...18 Endocrine and Molecular Inter-relationship of the E strous Cycle ..................................21 Follicular development ............................ ................................................... ..............21 Luteal function and Corpus Luteum regression ...... .................................................25 Manipulation of the Estrous Cycle ................. ................................................... .....................27 Pre-synchronization Programs ...................... ................................................... ................29 Timed Artificial Insemination Protocol ............ ................................................... ............32 Resynchronization Programs ........................ ................................................... ................35 Economics of Timed Artificial Insemination in the D airy Industry ..................................... ..38 Bull Aspects ...................................... ................................................... ...................................42 Use of Bulls as Natural Service in U.S.A .......... ................................................... ...........42 Bull Behavior, Evaluation and Factors Affecting Fer tility ............................................ .43 Semen Quality ..................................... ................................................... .........................49 Sperm Pathologies ................................. ................................................... .......................50 Head abnormality of sperm ......................... ................................................... ..........51 Midpiece and tail abnormalities of Sperm .......... ................................................... ..53 Cytoplasmic droplets of Sperm ..................... ................................................... ........55 Venereal Diseases in Bulls ........................ ................................................... ..........................56 Comparison of Natural Service and Artificial Insemi nation ............................................ ......60 3 COMPARISON OF REPRODUCTIVE PERFORMANCE IN LAC TATING DAIRY COWS BRED BY NATURAL SERVICE OR TIMED ARTIFICIAL IN SEMIANTION ...72 Introduction ...................................... ................................................... ....................................72 Materials and Methods ............................. ................................................... ...........................73 Animals, Housing and Diets ........................ ................................................... .................73 Study Design, Treatments and Exclusion Criteria ... ................................................... ....73
7 Timed Artificial Insemination Reproductive Manageme nt .............................................74 Natural Service Reproductive Management ........... ................................................... ......75 Pregnancy Loss .................................... ................................................... .........................76 Bull Management ................................... ................................................... ......................76 Milk Production Data and Body Condition Score ..... ................................................... ...77 Temperature Humidity Index ........................ ................................................... ...............78 Blood Sampling and Evaluation of Cyclicity ........ ................................................... .......78 Health Disorder Monitoring Program and Treatments ................................................... 79 Statistical Analysis .............................. ................................................... .........................80 Results............................................ ................................................... ......................................81 Assessment of Bulls ............................... ................................................... ......................81 Reproductive Performance .......................... ................................................... .................81 Parity, Body Condition Score and Milk Production .. ................................................... ...82 Cyclic Status, Seasonality and Health Disorders ... ................................................... ......83 Pregnancy Loss .................................... ................................................... .........................84 Discussion ........................................ ................................................... ....................................84 Conclusion ........................................ ................................................... ...................................88 4 FINANCIAL ANALYSIS OF DIRECT COMPARISON OF NA TURAL SERVICE SIRES AND TIMED ARTIFICIAL INSEMINATION IN A DAIRY HERD ....................100 Field Study ....................................... ................................................... ..................................101 Herd Budget Calculator ............................ ................................................... ..................103 Sensitivity Analysis .............................. ................................................... ......................106 Results............................................ ................................................... ....................................107 Field Study ....................................... ................................................... ...........................107 Sensitivity Analysis .............................. ................................................... ......................108 Discussion ........................................ ................................................... ..................................111 Conclusion ........................................ ................................................... .................................114 5 GENERAL DISCUSSION AND CONCLUSIONS ........... ................................................... 123 LIST OF REFERENCES ................................ ................................................... ..........................125 BIOGRAPHICAL SKETCH ............................... ................................................... .....................146
8 LIST OF TABLES Table page 2-1 Criteria for determination of stages of the est rous cycle ........................................ ...........67 3-1 Reproductive responses for TAI and NS ......... ................................................... ...............89 3-2 Twenty-one day cycle pregnancy rates for each c ycle for TAI and NS ............................90 3-3 Effect of health disorder on proportion of preg nant cows to the first 21 days breeding ...91 3-4 Pregnancy loss for TAI and NS ................. ................................................... .....................92 4-1 Partial budget for NS ......................... ................................................... ...........................115 4-2 Partial budget for TAI ........................ ................................................... ...........................116 4-3 Returns and costs per slot for TAI and NS ..... ................................................... ..............117 4-4 Simulated scenarios for TAI and NS not accounti ng for difference in reproductive performance obtained at the study Lima et al. at ch apter 3 ........................................... ..118 4-5 Simulated scenarios for TAI and NS accounting f or difference in reproductive performance obtained at the study Lima et al. at ch apter 3 ........................................... ..119 4-6 Different PR in variables scenarios for TAI and NS accounting for difference in reproductive performance obtained at the study Lima et al. at chapter 3 ........................120 4-7 Different PR in variables scenarios s for TAI a nd NS not accounting for difference in reproductive performance obtained at the study Lima et al. at chapter 3 ........................121 4-8 Opportunity cost provided by the replacement of bulls by lactating cows ......................122
9 LIST OF FIGURES Figure page 2-1 Continuity and interactions of events occurring during the estrous cycle ......................... 68 2-2 Net present values of reproductive management p rograms for second-lactation cows .....69 2-3 Guidelines for Breeding Soundness Evaluation 1 ................................................... ..........70 2-4 Guidelines for Breeding Soundness Evaluation 2 ................................................... ..........71 3-1 Timeline of reproductive events to the 1st service for TAI and NS ........................... ........93 3-2 Timeline of reproductive events to the followin g for TAI and NS................................... .94 3-3 Survival curves for proportion of non-pregnant cows for TAI and NS .............................95 3-4 Survival curves for proportion of non-pregnant primiparous and multiparous cows ........96 3-5 Survival curves for proportion of non-pregnant cows with BSC £ 2.75 or 3.0 ................97 3-6 Survival curves for proportion of non-pregnant heat stressed and thermoneutral cows ....98 3-7 Survival curves for proportion of non-pregnant for healthy and at least one disease event .................................................. ................................................... ..........................99
10 LIST OF ABBREVIATIONS AI Artificial insemination BCS Body condition score BSE Breeding soundness evaluation CL Corpus luteum CR Conception rates DNA Deoxyribonucleic acid E2 Estradiol GnRH Gonodorelin release hormone LH Luteinizing hormone mRNA Messenger ribonucleic acid NAHMS National animal health monitoring system NRR Non-return rates NS Natural service P4 Progesterone PGE2 Prostaglandin E 2 PGF2 a Prostaglandin F-2 alpha US Ultrasonography examination U.S.A. United States of America VWP Voluntary waiting period
11 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science COMPARISON OF REPRODCUTIVE PERFORMANCE AND COST OF NATURAL SERVICE AND TIMED ARTIFICIAL INSEMINATION IN LACTAT ING DAIRY COWS IN FLORIDA By Fbio Soares de Lima August 2009 Chair: Name Carlos Risco Major: Veterinary Medical Sciences Objectives were to compare reproductive performance cost and profitability of lactating dairy cows bred by natural service and timed AI. On e thousand and fifty-five cows were blocked by parity and randomly enrolled to receive either N S or TAI. Cows in both groups were presynchronized with 2 injections of PGF2, given 14 d apart. TAI group receveid an Ovsynch protocol and were re-synchronized with CIDR inserte d 18 d after TAI and removed 7 d later, when GnRH was given. Cows were examined by US on d 32 after TAI; non-pregnant cows received PGF2 and GnRH 56 h later followed by TAI 16 h after the GnRH injection. Nonpregnant cows in TAI group were re-inseminated up t o 5 times using the same scheme. Cows in the NS group were exposed to bulls 14 d after the e nd of the pre-synch protocol and US was performed 42 d after exposure to bulls. Non-pregnan t cows in the NS group were re-examined by US every 28 d until diagnosed pregnant or 223 d pos t partum (pp), whichever occurred first. Cows diagnosed pregnant in TAI or NS were re-confir med 28 d later to determine pregnancy loss. All bulls underwent a BSE and were rested for 14 d after 14 d of cow exposure. Health disorders, BCS and cyclic status were evaluated. An economical model was created using
12 Microsoft Excel 2007 (Microsoft Corporation, Redmond, WA, U.S.A.) to account for a ll costs, return and opportunity cost involving NS and TAI. T he proportion of pregnant and 21-d cycle pregnancy rate cows in the first 21 d of breeding d id not differ between groups. The daily rate of pregnancy was 15% greater for NS than TAI because c ows in NS had a greater pregnancy rate, which resulted in fewer median d open (111 vs. 116 d). Proportion of pregnant cows at 223 d postpartum was greater in the NS than TAI group (84 .2% vs. 74.8%, respectively). The daily rate of pregnancy tended to increase with a concurrent i ncrease in milk yield. Cows with BCS 2.75 cows had greater proportion of pregnant cows in the first 21 d of breeding and daily pregnancy rate in the first 223 d post partum Primiparous cow s had greater proportion of pregnant cows and daily pregnancy rate than multiparous cows at 223 d post partum. Direct net cost of the NS and TAI program during the trial were $100.53/cow/yr an d $61.84/cow/yr, respectively. Costs per eligible day were estimated $1.44 for NS program an d $0.90 for the TAI program. The advantage of the TAI program was $38.69/cow/yr. Whe n the differences in voluntary waiting periods and PR obtained were accounted the economic advantage of TAI over NS was $10.00. The advantage of the TAI program was $22.75 if gene tic advantage of TAI was not considered. Sensitivity analysis revealed that if the marginal feed cost increase from $2.00 to $8.00 the profit of TAI over NS rose for $144.81. Considering opport unity cost, if each bull was replaced by an additional cow the advantage of the TAI program was $68.82/slot/yr. Changing PR for each program for 12.0% resulted in an advantage of $75.3 9/cow/yr for the TAI program. In conclusion, NS had a better reproductive perform ance than TAI. The higher proportion of pregnant cows in the NS group can be attributed to a greater opportunity for breeding than in TAI. The TAI breeding program was less expensive th an NS even when the benefits on reproductive performance and VWP for NS obtained in our study were accounted.
13 CHAPTER 1 GENERAL INTRODUCTION Reproductive performance of dairy cows has declined during the last 50 years in the US and other countries, as shown in studies that compa red pregnancy per artificial insemination (AI) from the 1950 s to recent years (Lucy et al. 2001, Jorristma and Jorristma 2000 and Lpez-Gatius 2003), which has impacted profitability of dairy pr oducers. Concurrently, AI has been established as the preferred method to breed cows s ince its commercial development in the 1950s (Vishwanah, 2003). Dairy producers worldwide have b enefitted from the use of semen from progeny tested bulls used to breed dairy cows. With the use of AI, the risk for venereal disease is eliminated and the incidence of dystocia is reduced as well as human accidents caused by bulls with bad temperament. Furthermore, a better dry cow management occurs with AI because of more accurate drying off and calving dates (Vishwan ah, 2003). Moreover, increasing rate of genetic change in dairy breeds, and in particular, increases in milk yield with the use of AI has been reported. Daughters of AI sires produced 113 t o 136 Kg more of milk per year than daughters from sires used for NS (Norman and Powell 1992). De Vries (2008) reported that in a U.S.A. herd prod ucing 20,000 lbs of milk, 1 unit of pregnancy rate is valued between $22 and $35 when p regnancy rate range from 15 to 19%. Similarly, an extra day open beyond 90 days costs b etween $1 and $5, with an increasing cost as days in lactation progresses (De Vries, 2008). Despite these considerable advantages for AI, a sig nificant number of dairy producers use NS for their breeding program. In a survey on bull management practices in California, 84% of the producers reported use of NS as a component of their breeding program (Champagne et al. 2002). The most common use of NS was after unsucces sful AI attempts. In dairy herds located
14 in the northeast region of the US, reported use of NS, as a component of the breeding system, varied from 55% to 74% (NAHMS, 2002; Smith et al. 2 004). In a study that compared pregnancy rates (PR) between AI and NS in Georgia a nd Florida dairy herds, the use of NS alone or in combination with AI was reported to be around 70% (De Vries et al. 2005). A survey that examined management practices in 103 herds particip ating in the Alta Genetics (Watertown, WI) Advantage Progeny Testing Program, reported that 43 % of herds used a clean-up bull (Caraviello et al. 2006). Non-pregnant cows were mo ved to the clean-up pen after six unsuccessful AIs or 232 d post partum (pp). A comm on perception among these dairy producers that use NS is that NS is comparable to AI because human errors in estrous detection are avoided when bulls are used. Estrous detection is a major factor that impairs re productive performance and profitability of lactating dairy cows (Pursley et al. 1997a). Tim ed artificial insemination and NS are two breeding systems that are used by dairy producers t o mitigate the reduced fertility caused by inefficient low rates of estrous detection. Natural service, notwithstanding all the recognized advantages of AI previously mentioned still is used widely throughout the U.S.A. Dairy producers have the common perception that NS is the cheapest and easiest strategy to improve problems related to estrous detection. However, a p aucity of research exists to support this premise. Overton (2005) compared the cost of AI and NS using a partial budget approach to stochastically model the expected costs and returns of reproductive management of NS or AI. Option one was NS managed using currently recommend ed approaches including breeding soundness evaluations, bull vaccination, and a rota tional breeding system and option two was an AI system using a modied Presync-Ovsynch timed AI program in conjunction with estrus detection and inseminations. Under the models assu mptions, the use of NS sires averaged U.S.
15 $10 more in cost per cow per year as compared to an AI program. Nevertheless, that study considered a combination of TAI and estrus detectio n, which does not exclude estrus detection in the equation of reproductive performance. Furthermo re, several assumptions were done in attempting of obtain the closest scenario of the pr edominant dairy farm in the Western region of the U.S.A., which not necessarily reflects the real ity in the several different scenarios throughout of the U.S.A. In addition, the use of TAI solely ha s been reported to be more economical than AI at detected estrus (Risco et al., 1998; LeBlanc 20 01) due to reductions in days non-pregnant and cows culled due to infertility. However, studies th at compare costs and profitability and reproductive performance of NS and TAI, two breedin g systems where estrous detection is not required, using a random allocation design are lack ing. The hypothesis was that the use of TAI would result in a greater proportion of pregnant co ws than NS. Our biological justification and rationale for improved reproductive performance wer e that TAI cows undergo ovulation and synchronization of follicular wave and all eligible cows are inseminated at a fixed time, which results in greater proportion of pregnancy right af ter voluntary waiting period where the value of the pregnancy is greater increasing the chance for profit. Therefore, the objectives of this study were to compare reproductive performance, costs and profitability of lactating dairy cows bred by TAI or NS, two breeding systems that do not requ ire estrus detection, as the sole reproductive program on a commercial dairy farm located in north central Florida.
16 CHAPTER 2 LITERATURE REVIEW Reproductive Performance of Lactating Dairy Cows Reproductive performance in lactating dairy cows is characterized as the ability of obtaining one live calf as soon as possible after t he end of the voluntary waiting period. Reproductive performance is affected by several fac tors that include: fertility, embryonic and fetal development, calving and calf survival. Ferti lity generally is assessed by reproductive responses such as: conception rate (CR), pregnancy rate (PR), cyclic status and non-return rates (NRR). Consistently throughout the world several studies h ave reported a remarkable decline in fertility of dairy cows in the past few decades. In the U.S.A., the conception rate at first artificia l insemination (AI) has decreased by 0.45% per year o ver a 20-year period (Butler and Smith, 1989; Beam and Butler, 1999). In Spain, PR to cows AI between days 45-70 postpartum decline from 42.3% to 33.1% with an increase of 4.6% in ova rian inactivity between 1991 and 2000 (Lopez-Gatius et al. 2003). In England, this reduct ion has been in the magnitude of 1% per year in the last 40 years (Royal et al. 2000a; Royal et al. 2000b). In the Netherlands, the success rate to first AI decreased from 55.5% to 45.5% in 10 yea rs (Jorristma et al. 2000.) In the U.S.A. Lucy (2001) reported an increase in the number of AIs r equired for conception, from 1.75 to more than 3 over a period of 20 years. In Ireland, Mee e t al. (2004) reported a higher number of AIs per cow 1.75 vs. 1.54 and a decrease in CR from 64. 9% to 57.1% between 1990 and 2000 in pasture based system. In France, Bousquet et al. (2 004) reported that from 157,630 first AIs per year, there was a 15% decrease in the NRR. In Canad a the analysis of insemination data of Canadian Holstein cows between 1995 and 2001 showed a decrease in the NRR rate at 56 days from above 69% down to 67% (VanDoormal, 2002) and C R at first and second AI, respectively,
17 has been continually on the decrease from 44% to 39 % and 47% to 41% between 1990 and 2000 (Bouchard et Du Tremblay, 2003). The impairment in fertility is a combination of a d iverse physiological and management factors that have an additive effect on reproductiv e efficiency. Amongst these factors the possible modernization of the dairy cow and farm to meet the industry required demands for a more efficient production of milk possibly have aff ected reproductive performance of dairy cows. This modernization was achieved by a rapid progress in animal genetic improvement towards milk production and management. The genetic advance was obtained through the selection of more productive animals facilitated by the use of AI. However, the intense use of AI until the middle 90s relied on intensity and accur acy of estrus detection and conversely cows that produce more milk are less likely to show sign s of estrus. In addition, the increase of herd size has made more difficult to monitor lactating d airy cows daily on an individual basis for estrus behaviour. Timed Artificial Insemination (TAI) was a program r eported by Pursley et al. (1995) with the purpose of synchronizing ovulation and insemina te at a fixed time and consequently eliminate estrus detection in the equation of repro ductive efficiency. Despite the success of the TAI program to eliminate difficulties with estrus d etection, which results in economic and reproductive performance advantages when compare to AI at detected estrus (Pursley et al. 1997a; Burke et al. 1996; Pursley et al. 1997b; Car tmill et al. 2001, Risco et al. 1998 and LeBlanc 2001), the use of NS to breed dairy cows is still widely used throughout the U.S.A. to mitigate the decline in fertility related to poor e strus detection (NAHMS, 2002; Smith et al. 2004; De Vries et al. 2005; and Caraviello et al. 2 006). The range of reported use of NS in the
18 U.S.A. varies from 43% (Caraviello et al. 2006) as clean up bulls in herds using high quality genetics to 84% when used as a component of the bre eding program in California (Champagne et al. 2002) and 70 % in Florida and Georgia (De Vries et al, 2005) Estrous Cycle of Dairy Cattle Period, Stages and Classifications of the Estrous C ycle The estrous cycle is a period of reproductive cycli city initiated after puberty that continues for the entire life of dairy cows only being interr upted by pregnancy, nursing, nutrition deficiency and inadequate environmental conditions. In addition, pathologic conditions of the reproductive tract such as: pyometra, uterine infec tion, follicular cyst, persistent corpus luteum (CL) and mummified fetus also interrupt the estrous cycle. The estrous cycle is composed of a series of correlated and expected events that start and end between two consecutive estrous events periods marked by behavioral events of sexua l receptivity and copulation. The estrous cycle provides females repeated opportunities to be come pregnant in intervals of 21 days. Dairy cattle are categorized as polyestrus and consequent ly can become pregnant independent of the season of the year (Asdel, 1964). The estrous cycle can be divided in follicular and luteal phases that are classified according to the predominant structure present in the ovaries The luteal phase takes place after ovulation and lasts until regression of the CL, which general ly corresponds to 80% of the estrous cycle duration (Senger, 2003). During the luteal phase pr ogesterone (P4) is the predominant hormone produced and controls physiological events of the c ycle. In addition, during the luteal phase, it is noticeable that follicular growth continues as well as atresia of follicles that do not ovulate. The production of estradiol (E2) by the follicles is inhibited by P4 during the luteal phase. The follicular phase starts after regression or luteoly sis of the CL with a concomitant reduction in P4 concentration. With the reduction of P4, the gonodotropins FSH and LH are released from th e
19 hypothalamus, which stimulate the production of E2 and is the predominant hormone during the follicular phase in association with low levels of P4. As E2 increases an LH peak occurs which results in ovulation between 24 to 30 hours. The fo llicular phase ends with the behavioral event of estrus. The estrous cycle is classified in four stages, pro estrus, estrus that are considered subdivision of the follicular phase and metestrus a nd diestrus that are subdivision of the luteal phase. Proestrus starts when P4 declines as a result of luteolysis caused the acti on of PGF2 a and it lasts 2 to 5 days. Proestrus is the stage where the major endocrine tr ansition events take place and is marked by the final maturation of the dominant follicle an d a significant concentration increase of E2. In addition, this is the stage in which P4 dominance is replaced by E2. FSH and LH orchestrate the recruitment and selection of the ovulatory follicle The pre-ovulatory follicle produces increased concentrations of E2 and prepares the uterus for the onset of estrus and mating. Estrus is the most recognizable stage of the estrou s cycle because the behavioral symptoms of sexual receptivity are expressed. Estradiol is t he hormone responsible for the behavior of estrus (stand to be mounted), which characterizes t his stage. Females that are in estrus are not initially receptive to other females. The acceptanc e of mounting only occurs at the second half of estrus. Initially, cows increase locomotion, displa y phonation (vocal expression), nervousness and attempts to mount other animals without accepti ng the male for matting. After certain progress in the continuity of estrus the female acc epts the male for matting. Metestrus is the transition between ovulation and f ormation of the CL. Progesterone and E2 are relatively low during this stage of the estrous cycle. The recently ovulated follicle develops into a CL through the process of luteinization, whi ch is accomplished by cellular and structural
20 renovation. Before formation of the CL there is a f ormation of a transitory structure named the corpus hemorrhagicum. Metestrus has P4 concentration detectable soon after ovulation, but the concentration will not increase significantly until 2 to 5 days after ovulation. Diestrus is the longest stage of the estrous cycle in cows lasting about 10 to 14 days in dairy cows and it is characterized by a fully funct ional CL with high concentration of P4 (3-6 ng/ml). This high P4 concentration prepares the ute rus for early embryonic development and eventual attachment of the conceptus to the endomet rium. The diestrus phase ends when the CL is lyzed by endometrial PGF2. Anestrous is a condition where cows do not cycle, w hich is characterized by inactive ovaries and neither ovulatory follicles nor functio nal CL are present (Senger, 2005). Bartolome et al. (2005), summarized the stages of t he estrous cycle based on clinical findings of the uterus and ovaries and are shown in Table 2-1. Hodgen (1982) described the process of follicular g rowth and development in primates as recruitment, selection, and dominance. Recruitment is a process whereby a cohort of follicles begins to mature in a milieu of sufficient pituitar y gonadotropic stimulation to permit progress toward ovulation. Selection is the process by which a single follicle is chosen and avoids atresia and undergoes further development and dependent upo n which follicular wave will achieve ovulation. Dominance is the means by which the sele cted follicle is through inhibits the growth and the recruitment of a new cohort of follicles. Wiltbank et al. (2002) classified critical follicul ar sizes accordingly with evaluation of follicular growth patterns by ultrasound combined w ith measurement of circulating reproductive hormones. The three functionally critical follicula r sizes during the final stages of follicular growth are: emergence (4 mm), deviation (9 mm), and ovulation (variable from 10 to 20 mm).
21 Follicular deviation was defined as the beginning o f the greatest difference in growth rates (diameter changes between successive ultrasound exa minations) between the largest follicle (i.e. dominant follicle) and the second largest follicle (i.e. largest subordinate follicle) at or before examination when the second largest follicle reache s its maximum diameter (Ginther et al. 1996). Selection of the dominant follicle either oc curs at the time of follicular diameter deviation or is closely associated with this process (Wiltban k et al. 2002). This classification based on the three critical points is logical and provides a rat ional diagnosis and treatment of the underlying physiological condition such as: anovulatory condit ions. Endocrine and Molecular Inter-relationship of the E strous Cycle Follicular development The endocrine control of the estrous cycle in cattl e is made up by the interface among the hypothalamus, anterior pituitary and reproductive t ract. The hypothalamus has a central role in controlling the follicular phase, because it is whe re gonodotropin release hormone (GnRH) is produced and released. The hypothalamus is divided in two different centers according to the different patterns of GnRH release. The first cente r of GnRH release is located at the ventromedial and arcuate nuclei and is called the t onic GnRH center. This tonic center is responsible for basal secretion of GnRH and is char acterized by various small pulses of GnRH of different frequencies and amplitudes. Conversely, t he other GnRH center located at the preoptic and suprachiasmatic nuclei at the superior anterior hypothalamic area are responsible for the preovulatory release of GnRH that causes an LH surg e and consequently ovulation. This center is called the surge center and is also referred to as the preovulatory center (Senger, 2005). The release of GnRH by the surge center is related to high estrogens concentrations in blood and is accompanied by low P4. In contrast, th e release of GnRH from the tonic center is spontaneous in nature, however it is influenced by high P4.
22 The mechanism of how E2 and P4 influence the release of GnRH in cattle is not completely understood. Dungan et al. (2006) reviewing studies in several mammalian species reported that kisspeptin stimulates the secretion of gonodotropin s from the pituitary by stimulating the release of GnRH from the forebrain after the activation of G protein-coupled 54, which is expressed by GnRH neurons. Kisspeptin is a family of peptides en coded by the gene Kiss 1, which bind to G protein-coupled receptor 54. Kisspeptin is expresse d in large quantities in the Arcuate nucleus and the anteroventral periventricular nuclei of the hypothalamus. Both E2 and testosterone regulate the expression of the Kiss1 gene in the Ar cuate nucleus and anteroventral periventricular nuclei; however, the response of th e Kiss1 gene to these steroids is exactly opposite between these two nuclei. Estradiol and te stosterone down-regulate Kiss1 mRNA in the Arcuate nucleus and up-regulate its expression in t he anteroventral periventricular nuclei. Thus, kisspeptin neurons in the Arcuate nucleus may parti cipate in the negative feedback regulation of gonadtropin secretion, whereas kisspeptin neurons i n the anteroventral periventricular nuclei may contribute to generating the preovulatory gonad otropin surge in the female. GnRH released by the tonic center early in the foll icular phase stimulates the release of FSH and LH in the anterior lobe of the pituitary. T hese two gonodotropins act directly in the ovaries stimulating the recruitment of a new follic ular wave. The mechanism that controls recruitment of these small follicles and determines which follicles are recruited is unknown, but increased concentrations of FSH in plasma after ovu lation may stimulate this process (Walters and Schallenberger, 1984). In addition, McNatty et al. (2006) reported that once follicular growth has been initiated, at least two oocyte-deri ved growth factors, namely growth differentiation factor 9 and bone morphogenetic pro tein 15, are critical for ongoing development to ovulation. This occurs most likely by regulating the proliferative and differentiates functions
23 of adjacent follicular cells. In sheep, the granulo sa cell populations doubles some 12-14 times, and a well-defined thecal layer differentiates befo re antrum formation and the time taken to complete this process varies between 50 -150 days w ith very little follicular atresia. During preantral growth, FSH and LH receptors coupled to t he cyclic adenine monophosphate second messenger system develop in granulosa and thecal ce lls, respectively. From the late preantral stage, growth differentiation factor 9, bone morpho genetic protein 15 and perhaps other factors are thought to regulate gene expression in cumulus cells to enhance metabolic cooperatively with the oocyte and mural granulosa cells to regulate th eir responses to pituitary hormones. In sheep, antral follicular development is characterized by a much faster rate of growth, additional increases in the numbers of granulosa (4-5 more dou blings) and theca cells, an increased level of steroid and inhibin secretion in response to FSH an d LH, but also by most follicles undergoing atresia. The final number of follicles that go on t o ovulate is dependent upon FSH, as well as the intrafollicular concentrations of growth differenti ation factor 9 and BMP15. The selection of the dominant follicle involves var ious factors. Cows that develop a dominant follicle have higher concentrations of E2 and inhibin A and lower concentration of FSH than cows without a dominant follicle (Buttler et a l. 2004). Fortune et al. (20040 summarized the role of intrafollicular insulin growth factor syste m in the selection process of the dominant follicle in cattle. The concentrations of E2 in the follicular uid are the hallmark of dominan t and preovulatory follicles and are associated with lowe r concentrations of low molecular weight (MW) insulin-like growth factor binding proteins -2 -4, and -5, which can prevent binding of insulin growth factor to its receptor. In addition, Fortune et al. (2004) reported that dominant and preovulatory follicles also have much higher levels of an insulin-like growth factor binding proteins -4/-5 protease activity, which is the bovi ne equivalent of the human insulin-like growth
24 factor binding proteins -4 protease and pregnancy-a ssociated plasma protein-A. Analysis of the temporal sequence of changes in, E2 low molecular weigh insulin-like growth factor bin ding proteins, free insulin growth factor, and pregnancy -associated plasma protein-A in the follicular uid suggested that an increase in pregnancy-associ ated plasma protein-A is the earliest biochemical difference detected in the eventual dom inant follicle and that follicular selection is the result of a progressive series of changes begin ning with the acquisition of pregnancyassociated plasma protein-A, which leads to a decre ase in insulin growth factor binding protein-4 and -5 and an increase in free insulin growth facto r, which synergizes with FSH to increase estradiol production. Co-dominant follicles, induce d by injection of small doses of recombinant bovine, FSH, contained levels of pregnancy-associat ed plasma protein-A similar to the single dominant follicle of control heifers in both follic les, supporting the hypothesized role of FSH in the induction of pregnancy-associated plasma protei n-A in the dominant follicle. Together, these results suggest a critical role for FSH-induced pre gnancy-associated plasma protein-A, and thus for free insulin growth factor, in the selection of the dominant follicle. Ireland et al. (2000) reviewed findings of several studies regarding follicular turnover and number of follicular waves in the bovine and conclu ded that either 2 or 3 follicular waves can occur and the assumption that the first follicular wave occurs right before estrus, the follicle of the last follicular wave during an estrous cycle re sults in the ovulatory follicle. Moore and Thatcher, (2006) described that early est rogenic follicles (i.e. d 3 of the first wave) contained mRNAs for the FSH receptor and the aromatase is elevated within the granulosa layer, and theca cells have increased abundances of LH receptor and 17 -hydroxylase, an enzyme required for production of androgen precurso rs for estrogen biosynthesis. However, there is an absence of LH receptor mRNA within the granulosa cells. Dynamic changes are
25 evident within the inhibin family in that dimeric i nhibins (i.e. >160 kDa) are elevated and the smaller (32to 34-kDa) dimer of inhibin is low in estrogen-active follicles. However, in estrogen-inactive follicles, the smaller inhibin di mer increases and the larger molecular weight forms are reduced. The increased secretions of E 2 and ovarian inhibin reach the pituitary gland through the circulation and lead to a decrease in p ituitary secretion of FSH. Lack of FSH prevents further growth of subordinate follicles, w hich are also non-estrogenic due to low concentrations of free insulin growth factor -I. On ce the dominant follicle reaches 10 mm approximately in dairy cows (i.e. after deviation), its granulosa cells begin to express LH receptors, and it can be induced to ovulate at appr oximately 12 mm in size. Continued growth and dominance of the dominant follicle beyond 10 mm appears to be dependent upon LH secretion. Eventually, in the absence of an increas e in pulse frequency of LH, the dominant follicle undergoes functional atresia that permits an increase in FSH secretion. Luteal function and Corpus Luteum regression Progesterone produced by the CL plays a key role in regulation of the length of the estrous cycle in cattle and in the implantation of the blas tocyst (Niswender et al. 2000). Cholesterol, which can be derived from the diet in rare occasion in dairy cows and is actually in mostly of the time is synthesized de novo (Block, 1965 and Schoro epfer, 1982) is transported to the ovaries by lipoproteins (high density lipoprotein and low dens ity lipoprotein) and is a common precursor for steroids synthesis. Progesterone among others stero id hormones is the most important physiological regulator involved in the CL life spa n and implantation of the blastocyst. Ovarian steroidogenesis is regulated by several factors pla ying modulatory role during the estrous cycle. Centrally and locally produced factors modulate exp ression of genes encoding synthesis of steroidogenic enzymes and consequently influence th e secretory function of the CL. Preovulatory surge of LH is crucial for the luteini zation of granulosa and theca follicular cells
26 and CL maintenance; however, the CL is less depende nt on LH stimulation during the early luteal phase. Since the early CL requires luteotrop ic support for its growth and development, there are other factors that support the role of LH to maintain CL development and function. Indeed, hormones of luteal origin i.e. prostaglandi ns (PG) I2 and E2, oxytocin, noradrenaline and growth factors stimulate P4 synthesis in the bovine early CL (Niswender et al. 2000; Miszkiel and Kotwica, 2001). Therefore, it is accepted that despite hormonal and neural signals, which are fundamental in the estrous cycle, the CL has a broa d area of autonomy. Corpus luteum selfregulates synthesis of P4 (Kotwica et al. 2002), wh ich truly affects transcription of genes encoding steroidogenic enzymes (Rekawiecki et al, 2 005 and Rekawiecki and Kotwica, 2007). Moreover, high P4 concentrations in luteal cells pr otect them against apoptosis, while disruption or impairment of steroidogenesis or reduced ability of P4 production induces luteal cells death. Luteolysis is the process of destruction of the CL mediated by the action of mainly PGF2 that reaches the ovaries through a venous and arter ial counter current system described by Mapletoft et at 1976. Due to anastomoses of the ute rine vein to the contralateral ovary and ovarian artery ipsilateral to the CL, PGF2 produced in the uterus reach the CL bearing ovary a nd cause luteolysis. Skarzynski ank Okuda (2000) proposed that the mecha nism controlling development, maintenance and secretory function of the CL might involve factors that are produced both within the CL and outside the ovary. Some of these regulators appear to be prostaglandins and other arachidonic acid metabolites (PGE2, PGF2, leukotrienes), neuropeptides (noradrenaline), peptide hormones (Oxytocin, Endothelin 1), growth f actors and hormones (vascular endothelial growth factor, fibroblast growth factor, growth hor mone, prolactin), and steroids (P4 and E2) that act as autocrine and or paracrine factors. Althou gh PGF2 is known to be the principal luteolytic
27 factor, it is action on the CL is mediated by other intra-ovarian factors: cytokines, nitric oxide, Endothelin 1. Nitric oxide, Tumor necrosis factor a lpha in combination with interferon tau reduced P4 secretion, increased luteal PGF2 concentration, and induced apoptosis of the luteal cells (Skarzynski et al. 2008). Manipulation of the Estrous Cycle The implementation of AI became the preferred metho d to breed dairy cows since its commercial development in the 1950 s (Vishwanah, 20 03). However, the decline in fertility in dairy cattle (Lucy et al., 2001) associated with an increased difficulty to detect cows in estrus (Pursley et al., 1996) has required a better unders tanding of manipulation of the estrous cycle to synchronize estrus. The aim of a successful estrous synchronization pro gram is the control of ovulation permitting fixed-time AI without the need for estro us detection. Reproductive efficiency of lactating dairy cows measured by pregnancy rates (P R; defined as the proportion of pregnant cows relative to all eligible cows inseminated or n ot, in a given period of time) is greatly affected by poor estrous detection and anestrous (Thatcher a nd Santos, 2007). Thatcher et al. (2004) reported that a simultaneous expansion of the knowledge of the estrous cycle and appropriate implementation of phy siological methods to control sequential follicle turnover, CL regression and induction of o vulation have been achieved successfully in the past few years. In the 1970 s, Lauderdale et al. (1974) and Hafs an d Manns (1975), reported reproductive management protocols that synchronized the time of estrus using PGF2. Synchronization with PGF2 was successful in cows bred to a detected estrus, because estrus detection rates increased and management of AI was more efficient than daily detection of estrus alone (Stevenson et al. 1994). Nevertheless, this manipulation of the estru s detection using PGF2 did not control the
28 time of AI, because estrus detection continued to b e necessary. Lauderdale et al. (1974), Archbald et al. (1992), Lucy et al. (1986) and Stev enson et al. (1987) evaluated fixed-time breeding TAI after PGF2 in lactating dairy cows. Pregnancy rates per AI we re substantially lower than those AI at detected estrus. Low pregnan cy rates from timed AI using PGF2 can be explained by the fact that PGF2 alone does not result in an optimal synchronizatio n of ovulation in relation to AI because time of ovulation depends on the stage of dominant follicle development in concert with the prostaglandin-induc ed regression of the CL. Therefore, strategies were developed in an attempt to resolve the problem of TAI in dairy cows without the need for estrus detection. Pursley et al. (1995) re ported the development of the Ovsynch protocol, a TAI breeding strategy that resulted in acceptable pregnancy rates. The Ovsynch protocol is composed of an injection of GnRH at a r andom stage of the estrous cycle to induce ovulation of the dominant follicle and synchronize the emergence of a new follicular wave. Seven days later, PGF2 is given to regress both the original and induced CL, followed by a second GnRH injection 48 h later to induce ovulatio n approximately 28 to 32 h later. A timed AI is performed 12 to 16 h after the second GnRH injec tion. Pregnancy rates obtained from the Ovsynch program were comparable to those of cows in seminated at detected estrus (Pursley et al. 1997a). This protocol has been implemented succ essfully in commercial dairy farms throughout the world as a strategy for TAI to the f irst postpartum AI, as well as for reinsemination of non-pregnant cows. Although, the Ov synch protocol allows for TAI without the need for estrus detection, approximately 10 to 15% of cows will come in estrus during the protocol and should be AI to optimize PR. Schimitt et al. (1996) also contributed to developm ent and consolidation of TAI as an option to inseminate cows at a fixed time without e strous detection. Schimitt conducted a series
29 of three experiments to evaluate the efficacy, timi ng and replacement of the last GnRH of the TAI protocol. In experiment 1, dairy heifers were a ssigned randomly to two groups: 1) TAI, consisting of GnRH on d 0, PGF2 injection on d 7, and second GnRH injection on d 8 and AI on d 9; and group 2) AI at estrus (AIE), consisting of GnRH on d 0, PGF2 injection on d 7 and AI at detected estrus. Pregnancy rate was 25.8% for TA I compared with 48.7% for AIE ( P < .001). Experiment 2 was comparable to experiment. 1, but t he second GnRH in TAI was given 48 h after injection of PGF2. Heifers in TAI were inseminated at detected estru s if estrus occurred within 39 h after administration of PGF2. In experiment 2, PR were 45.5% for TAI and 48.0% for AIE (P>0.1) and CR rate was greater (P < .005) in AIE (61.2%) than TAI (45.5%). In experiment 3, the second injection of GnRH agonist, given at 48 h after injection of PGF2a, was replaced with hCG. No differences in PR were detect ed for TAI (52.9%) vs AIE (56.1%) and CR was worse (P < .005) for TAI (52 %) than AIE 72.3%. Delaying th e second GnRH agonist injection by 24 h improved pregnancy rate, but repl acing the second injection of GnRH with an injection of hCG did not prevent a reduction in con ception rate Despite the relative success of the Ovsynch protoco l that eliminates the need for estrus detection, the poor reproductive performance contin ued to be observe in lactating dairy cows warranted further research to optimize pregnancy ra te with the use of Ovsynch. Pre-synchronization Programs Vasconcelos et al. (1999) reported that initiation of the Ovsynch protocol between days 5 and 9 of the estrous cycle resulted in the highest frequency of ovulation to the first GnRH injection. Fertility was decreased when the durati on of dominance of the ovulatory follicle was longer than 5 days (Austin et al. 1999) or the Ovsy nch program was initiated in the early stages of the estrous cycle (Vasconcelos et al. 1999). Ov ulation to the first GnRH injection and initiation of a new follicular wave should improve PR per AI because an ovulatory follicle with a
30 reduced period of dominance is induced to ovulate. Based on that theory, the concept of presynchronization was developed by Moreira et al. (2001) to enhance the likelihood of having a dominant follicle ( 10mm) capable to ovulate to the first GnRH injecti on in the Ovsynch protocol and assurance that a CL would be present t hroughout the synchronization period i.e. the CL will not regress prior to the injection of PGF2. The Presynch-Ovsynch program by Moreira et al. (2001) employs two injections of PGF2 14 days apart, with the second injection given 12 days prior to the first GnRH of the Ovsynch protoco l. This program increased PR per AI 18 percentage units (25% to 43%) in lactating dairy co ws that were cycling cyclic. Similarly, ElZarkouny et al. (2004) also reported improvement in PR when cows were pre-synchronized prior to the Ovsynch protocol. In addition to the potenti al benefit of optimizing the stage of the cycle by presynchronization, the prior repeated injecti ons of PGF2 might have a therapeutic benefit on the uterine environment by stimulating re-occurr ing proestrous/estrous phases allowing for improved uterine defense mechanisms. Navanukraw et al. (2004) demonstrated that presynchronizing cows with 2 injections of PGF2 the second given 14 days prior to initiation of th e Ovsynch protocol, improved PR compared to Ovsynch a lone. Considering the same rationale for enhancing ovulat ion to the first GnRH of the Ovsynch program to improve CR, Bello et al. (2006) compared three different pre-synchronization protocol before the Ovsynch. Prostaglandin was giv en and then 2 days later GnRH was given either 4, 5 or 6 days before starting Ovsynch. The ovulation rates to the first GnRH of Ovsynch were 56.0, 66.7, 84.6, and 53.8% for presynchroniza tion protocols given with GnRH given either 4, 5 and 6 days prior Ovsynch, and no presynchroniz ation, respectively, and was greater for GnRH given 6 d before Ovsynch than for control cows Luteolytic response to PGF2 in the Ovsynch protocol was greater in all treated groups than for control (92.0, 91.7, 96.2, and 69.2%
31 for presynchronization protocols with GnRH given ei ther 4, 5 and 6 days prior Ovsynch, and controls, respectively,). Synchronization rate to O vsynch was greater (92 vs. 69%) in G6G than in control cows, respectively. In addition, cows th at ovulated in response to the rst GnRH had greater response to PGF2 (Ovulation: 92.7; No ovulation: 77.1%) and a grea ter synchronization rate to the overall protocol (Ovula tion: 87.9; No ovulation: 62.9%,). Concentrations of progesterone on the day of PGF2 injection in the Ovsynch protocol, and estradiol and follicle size at the nal GnRH of Ovs ynch, were identied as signicant predictors of probability of pregnancy 35 d after articial in semination. Galvo et al. (2007) compared three different pre-s ynchronization protocols with outcome of interest being ovulation to the first GnRH, pres ence of a CL at PGF2 and PR per AI in a TAI protocol. Galvo et al. (2007) used the presynch-Ov synch protocol with two injections of PGF2 given 14 days a part and the TAI protocol started e ither at 11 or 14 d later (Control). Also, a third group received the two PGF2 14 d a part, 4 d later an injection of GnRH followe d by a TAI protocol 7 d later. Altering the interval between presynchronization an d the first GnRH of the TAI program did not affect the proportion of cows with a CL at 1st GnRH, but GnRH 7 d before the 1st GnRH of the TAI program increased the proportion of cows with a CL. Ovulation to the first GNRH of the TAI program was greater for 11 d interval compa red with the 14 d interval, but GnRH did not further improve ovulation. The increased ovulat ion to 1st GnRH of the TAI when the interval was reduced from 14 to 11 d was observed only in co ws with a CL at 1st GnRH of the TAI protocol. Treatment did not affect ovulation in cow s without a CL at the 1st GnRH of the TAI program. Treatment affected the pregnancy per AI on d 38 and 66 after insemination, and they were greater for the 11 compared with 14-d interval but addition of GnRH did not improve
32 further pregnancy per AI. Cows ovulating to the fir st GnRH had greater pregnancy per AI regardless of whether or not they had a CL at the f irst GnRH Reducing the interval from presynchronization to initiation of the timed AI pr otocol from 14 to 11 d increased ovulation to the first GnRH and pregnancy per AI in lactating da iry cows. The benet of reducing the interval from presynchronization to the timed AI protocol fr om 14 to 11 d was likely the result of improved ovulatory response to the first GnRH of TA I program because cows that ovulated had increased pregnancy per AI. Timed Artificial Insemination Protocol The difficulties in identifying lactating dairy cow s in estrus made crucial the development of new strategies to improve fertility. A major adv ancement in optimizing fertility in lactating dairy cows was the development of the Ovsynch TAI p rogram by Pursley et al. (1997a). Timed AI protocols such as Ovsynch, Cosynch 48 and Cosync h 72 have been successful in improving pregnancy rates by increasing AI submission rates. Ovsynch utilizes a nal treatment with GnRH that synchronizes the time of ovulation within an 8 -h period (Pursley et al., 1995). This precise timing of ovulation allows optimization of TAI in r elation to the time of ovulation. A number of studies have provided information relating to the o ptimal time for AI in a TAI protocol. A pivotal study on the optimal time for AI utilized t he original Ovsynch protocol and AI at 0, 8, 16, 24, or 32 h after the second GnRH treatment (Pursl ey et al., 1998). This study found a quadratic effect of time of AI on number of pregnancies per A I with CR increasing from 0 to 16 h with subsequent decreases from 24 to 32 h the expected t ime of ovulation. Nevertheless, only AI after the expected time of ovulation (32 h after nal GnR H) resulted in a signicant decrease in both percentage calving per AI and CR determined at the rst pregnancy diagnosis (Pursley et al., 1998).
33 Analysis of calving data suggested that AI at any t ime between 0 and 24 h after the nal GnRH resulted in similar rates of calving. Thus, th e study by Pursley et al., 1998, indicates that there may be an optimal time for AI ( < 16 h after nal GnRH) but also that there may be substantial exibility in the time for AI in relati on to ovulation, provided that AI is performed before ovulation. Insemination near or after the ti me of ovulation may provide insufficient time for optimal sperm capacitation and transport but re sults in an aged oocyte which compromises conception (Hunter and Wilmut, 1983; Wilmut and Hu nter, 1984; Hawk, 1987). Alternatively, excessive time from insemination to ovulation (>24 h) also appears to reduce fertility. Indeed, results from the earliest (Trimberger and Davis, 1943; Trimberger, 1944) up to the most recent studies (Dranseld et al., 19 98; Pursley et al., 1998; Saackeet al., 2000; Dalton et al., 2001) on time for AI have generally shown a decline in CR in cows inseminated at the onset of estrus or at the time of the LH surge (induced by GnRH treatment; Pursley et al., 1998) compared with later times. Decreases in ferti lization rate have been reported when cows were inseminated at the onset of estrus compared wi th breeding 12 or 24 h later (Dalton et al., 2001). Therefore, a loss of sperm viability is like ly responsible for the declines in fertilization rate and CR that have been observed in various (Tr imberger and Davis, 1943; Trimberger, 1944; Pursley et al., 1998; Dalton et al., 2001) but not all (Portaluppi and Stevenson, 2005) studies when a long intervals between AI and ovulation occu rred. Regardless of these results, the Cosynch protocol d eveloped by Geary and Whittier (1998) has become a popular TAI program among dairy produc ers. In the Cosynch protocol, AI is performed concurrently with the second GnRH injecti on, which requires one less time for cow handling, thereby potentially decreasing labor cost s, as well as other cow-handling problems associated with the utilization of a TAI protocol f or reproductive management. Some studies
34 have compared Cosynch to an Ovsynch protocol in whi ch cows were inseminated 24 h after the GnRH treatment. Vasconcelos et al. (1997) found tha t inseminating at 24 h after GnRH improved pregnancy compared with Cosynch at 48 h (C osynch-48). In contrast, two recent studies using only presynchronized rst-service ani mals found no difference in CR for animals receiving Cosynch at 48 h (AI 48 h after PGF) compa red with Ovsynch with a 24-h interval between the second GnRH and AI (Portaluppi and Stev enson, 2005; Cornwell et al., 2006). Portaluppi and Stevenson (2005) not only compared t hese 2 protocols in their study with presynchronized rst-service animals, but also incl uded a treatment group that received Cosynch at 72 h (Cosynch-72: AI 72 h after PGF). Cows in th e Cosynch-72 h group had better CR than cows in the other 2 groups combined, suggesting tha t delaying the time of nal GnRH as well as the time of AI may improve results from TAI, at lea st during the rst AI after Presynch. Nevertheless, the authors cautioned that this proto col has not been evaluated for synchronizing cows at second or later services (Resynch). Althoug h, Co-synch has become popular in the dairy industry, there are controversial results regarding whether this protocol produces CR that are similar to TAI protocols that AI at a time closer t o ovulation. Therefore, Cosynch are definitely not the best option to increase conception rates in a TAI program and is not recommended if the aim is of the TAI breeding system is to maximize re productive performance. Brusveen et al. (2007) compared the Cosynch 48 and 72 to a modified Ovsynch protocol, were the interval between the second GnRH and PGF2 was 56 h instead of the regular 48 hours and TAI was 16 hours after the second GnRH instead of 12 or 16 h as in the original Ovsynch. In addition, Brusveen et al. (2007) included cows pres ynchronized for all groups and used resynchronized services as well. The author found a n overall CR similar for the Cosynch-48 (29.2%) and Cosynch-72 (25.4%) groups. The Ovsynch56 group had a greater CR (38.6%) than
35 Cosynch-48 or Cosynch-72. Presynchronized rst-serv ice animals had greater CR than cows at later services in Cosynch-48 (36.2 % vs. 23.0%) and Ovsynch-56 (44.8 vs. 32.7%) but not in Cosynch-72 (24.6 vs. 26.2%). Similarly, primiparous cows had greater CR than multiparous cows in the Cosynch-48 (34.1 vs. 22.9%) and Ovsynch -56 (41.3 vs. 32.6%), but not Cosynch-72 (29.8 vs. 25.3%). Therefore, the author reported no advantage to Cosynch at 72 h vs. 48 h. Conversely, a clear advantage of treating with GnRH at 56 h to Cosynch 48 and 72 was observed, probably because of more-optimal timing o f AI before ovulation. Resynchronization Programs The high AI submission rate to rst TAI is often fo llowed by a time lag for the reinsemination of non-pregnant cows that depends on e strus detection efficiency and when pregnancy diagnosis is performed after AI. Because AI CR of high producing dairy cows are reported to be 40% or less (Pursley et al., 1997a, 1997b; Fricke et al., 1998; Jobst et al., 2000), 60% or more of cows that are TAI fail to conceive a nd thus require a resynchronization strategy for re-insemination. Combining diagnosis of non-pre gnant cows with a management strategy for a timely re-insemination improves reproductive effi ciency by decreasing the interval between AI services (Fricke, 2002). Moreira et al. (2000) reported an aggressive resync hronization protocol, in which cows received GnRH on d 20 after TAI followed by transre ctal ultrasound and PGF2 administration to non-pregnant cows on d 27. However, the authors fou nd an interaction for cows resynchronized with GnRH on d 20 after TAI that were treated with bovine somatotropin treatment and embryonic losses. From d 20 to 27 embryonic losses increased for bovine somatotropin-treated cows that received GnRH but not for non-bovine soma totropin-treated cows. Because of this observation, this resynchronization strategy was di scontinued. GnRH at 20 d after insemination adversely affected embryonic survival. The author c ogitated the possibility of an injection of
36 GnRH induces an immediate increase in plasma estrad iol concentrations, which may trigger the production of PGF2 by the endometrium and cause the demise of the CL. Moreover, Moreira et al. (2000) mentioned there is evidence that LH rece ptors are found in the uterine endometrium and uterine vein and that LH may stimulate PGF2 secretion. Hence, it is possible that an LH surge induced by an injection of GnRH may induce lu teolysis and did not ovulate to the rst injection of GnRH. Fricke (2002) proposed a resynchronization protocol in which groups of cows beyond the voluntary waiting period received their rst postpa rtum TAI after synchronization of ovulation. On d 18 after TAI, all cows received an injection o f GnRH regardless of their pregnancy status. Non-pregnant cows received a PGF2 injection on d 25 after TAI based on a non-pregnan cy diagnosis using ultrasound and continue with Ovsync h protocol, whereas pregnant cows would discontinue the protocol. Three different times to initiate the rst GnRH of the Ovsynch protocol (100 g GnRH, d 0, 25 mg PGF2, d 7, 100 g GnRH + TAI, d 9) for resynchronizatio n were compared at 19 (D19), 26 (D26), or 33 d (D33) aft er rst TAI to set up a second TAI service for cows failing to conceive. Conception rate was asses sed 26 d after TAI for D19 and D26 cows and 33 d after TAI for D33 cows. Overall CR to resy nchronization was 32%. However, the CR for D26 (34%) and D33 (38%) were greater than for D 19 cows (23%). Cows with a CL at the PGF2 injection (D19 cows) or at the rst GnRH injection (D26 + D33 cows) of resynchronization had greater CR to compared to cow s without a CL. Survival analysis (failure time) of cows in the D26 and D33 treatment groups a cross the rst three TAI services did not differ statistically. Although administration of Gn RH to pregnant cows 19 d after rst TAI service did not appear to induce embryonic loss, in itiation of resynchronization 19 d after TAI resulted in a lower CR compared to 26 or 33 d after TAI.
37 Chebel et al. (2003) compared resynchronization wit h GnRH on day 21 after a preenrollment of AI; animals assigned to the resynchro nization (RES) group received 100 g of GnRH, whereas animals in the control (CON) group re ceived no treatment. For RES and CON, pregnancy at day 21 based on P4 was 70.9% vs. 73.0% (P < 0:56), at day 28 33.1% vs 33.6% (P < 0:80) and at 42 days 27.0% vs. 26.8% (P < 0:98), respectively after the pre-enrollment AI. Administration of GnRH on Day 21 after AI had no ef fect on pregnancy loss in either the RES or CON group from days 21 to 28 (53.2% versus 53.5%; P < 0:94) and days 28 to 42 (17.9%; P < 0:74) after AI. Pregnancy after the resynchronizati on period was similar for both treatment groups. In this study, Chebel et al. (2003) did not find an effect of resynchronization with GnRH given on Day 21 after AI for initiation of a TAI pr otocol prior to pregnancy diagnosis on pregnancy or pregnancy loss in lactating dairy cows Sterry et al. (2006) compared two resynchronization TAI strategies at different days post AI; cows were assigned to receive the rst GnRH inj ection of Ovsynch at 26 (D26) or 33 (D33) days after TAI in cows that did not conceive. Cows in the D26 group received GnRH 26 d after TAI and continued resynchronization when diagnosed non-pregnant by using US at 33 d after TAI. Similarly, cows in the D33 diagnosed non-pregn ant received GnRH 33 days after TAI. Cows were classied based on the presence or absenc e of a CL at the non-pregnant diagnosis, and cows without a CL received an intravaginal prog esterone-releasing insert during the resynchronization protocol. When analyzed as a syst ematic strategy, CR was greater for cows assigned to the D33 than the D26 resynchronization strategy (39.4 vs. 28.6%). These results demonstrate that delaying the initiation of resynch ronization until 33 d after TAI increased PR/AI for primiparous cows. Silva et al. (2007) use PGF2 12 d before initiation of a protocol for resynchronization of ovulation using Ovsynch. Lacta ting Holstein cows diagnosed not pregnant
38 31 d after TAI were randomly assigned to initiate t he resynchronization protocol 32 d after TAI (RES), or receive 25 mg of PGF2 34 d after TAI and initiate the resynchronization protocol 12 d later at 46 d after TAI (PGF2 +RES). Cows in the PGF2 +RES group had better CR than RES cows 66 d after TAI (35.2 vs. 25.6%), whereas pregn ancy loss from 31 to 66 d after TAI was greater for RES than for PGF+RES cows (17.1 vs. 7.6 %). These results show that pretreatment with PGF2 12 d before initiation of the resynchronization Ovs ynch protocol improved P/ AI and decreased pregnancy loss from 31 to 66 d after TAI. However, this approach for resynchronization took longer time until re-insemin ation was performed. Economics of Timed Artificial Insemination in the D airy Industry Protocols for synchronizing ovulation in lactating dairy cows such as Cosynch and Ovsynch allows AI submission rates close to 100%, w hich improves pregnancy rate and reduces costs (Pursley et al., 1997a; Risco et al., 1998). Various studies compared Ovsynch to AI at detected estrus and several focused on conception a nd pregnancy rates after the rst synchronization (Britt and Gaska, 1998). In some st udies, Ovsynch was only used for the rst AI and then started observation of cows for estrus (De la Sota et al., 1998; Jobst et al., 2000; Klindworth et al., 2001). It has been recognized th at Ovsynch is more benecial in herds with poor estrous detection (Risco et al., 1998, Mialot et al., 1999, Tenhagen et al. 2004). However, the use of Ovsynch or other TAI program is completely dependent upon economic viability of the program, and the change o f workload when TAI is introduced is difficult to assess with accuracy, as well as time spent on detection of estrus, cow selection, organization and documentation. Risco et al. (1998) evaluated the economics of Ovsy nch TAI to insemination at detected estrus by simulating PR for each breeding system us ing computerized models. An economic advantage to Ovsynch TAI was attributed to a reduct ion in days non-pregnant and cows culled
39 for infertility. Further, the Ovsynch protocol was found to be more economical when applied during the warm season when estrus detection effici ency is low. Britt and Gaska (1998) compared PR, seasonal effect s, and economic benefits of 2 estrus synchronization programs for a confinement-housed d airy herd. These author included cows eligible for breeding after palpation per rectum an d randomly assigned to 2 treatment groups during 4 seasonal periods. Cows in one group (Ovsyn ch) received injections of GnRH on day 0, prostaglandin F2 alpha on day 7, and a second injec tion of GnRH on day 8. Cows in the other group (PP) that had a palpable CL were given PGF2. Estrus detection was not performed on the Ovsynch cows, which were artificially inseminated a t a predetermined time after the second GnRH injection. Cows in the PP group were observed for signs of estrus, and only those that were detected in estrus were inseminated. Pregnancy rates and insemination rates were significantly improved for cows in the Ovsynch grou p, compared with cows in the PP group. The Ovsynch program was an economically advantageous me thod for controlling reproduction that resulted in more pregnancies without the need for e strus detection. Similarly, LeBlanc et al. (2001) evaluated Ovsynch for repeated inseminations and reported an economic profit for TAI as a result fro m a reduction in the number of days open and decreased number of cows culled for reproductive pr oblems. Further benet occurred because fewer sub estrous cows were inseminated and diagnos ed per pregnancy status. Nebel and Jobst 1998, in a review that evaluated sy stematic breeding programs for lactating dairy cows focused on a hypothetical use of PGF2 and GnRH for estrus detection by conducting a survey of bovine practitioners. Using their survey results, they calculated an estimated cost per pregnancy for Ovsynch and Target ed Breeding (Pharmacia-Upjohn, Kalamazoo, MI). The costs per pregnancy for drugs a lone ranged from $5.75 for Targeted
40 Breeding with a 70% estrus detection rate to the le ast cost for drugs of $17.84 for Ovsynch at the mean costs for drugs. The authors advocated tha t as herd sizes and milk yield continue to increase, reproductive efficiency is pertinent to m aximizing profit. In addition, the authors suggested that systematic breeding programs have th e potential to increase the reproductive performance of lactating dairy herds while maintain ing AI as the primary breeding option. Primary benefits of systematic breeding programs in clude the convenience and efficiency of estrus detection; however, reduced labor costs from less time spent on estrus detection may be offset by the cost of the drug used in the protocol s. They concluded that cost effectiveness must be calculated for each herd to decide whether a sys tematic breeding program is the appropriate choice. Lastly, Nebel and Jobst speculated that per haps the cost of the programs could be recovered through increased convenience and decreas ed time spent observing cows for estrus. Tenhagen et al. (2004) compared the reproductive ef ciency and economic benet of Ovsynch protocols with conventional reproductive ma nagement in a eld trial in two large dairy herds in Germany. These authors compared a TAI bree ding protocol to insemination at detected estrus. Cows were synchronized for began the TAI pr ogram at 62 and 42 d in milk in herds 1 and 2, respectively. After TAI, cows seen in estrus rec eived AI, whereas cows diagnosed not pregnant were resynchronized for TAI. Control cows received AI based on detected estrus after a voluntary waiting period of 72 d in herd 1 and 50 d in herd 2. Use of Ovsynch reduced intervals to rst AI and days open in both herds and reduced culling for infertility in herd 2. CR for rst AI at detected estrus were signicantly higher comp ared to TAI in both herds and for overall AI at estrus in herd 2. For groups assigned to AI at e strus, mean 21-d submission rates over 200 d for AI were higher in herd 1 than in herd 2 (55.6 v s. 28.6%). Days open and culling were the major cost factors. Although Ovsynch improved repro duction in both herds, AI based on
41 detected estrus was economically superior in herd 1 whereas Ovsynch was superior in herd 2. This was consistent across the ranges of cost facto rs evaluated. Tenhagen et al. (2004) suggested that an evaluation of synchrony protocols should in clude reproductive performance along with appropriate costs associated with treatments. The a uthors concluded that such costs might balance benet to reproduction in herds with good e strus detection rates. Olynk and Wolf, 2008 reported in a survey from 57 f arms throughout the U.S.A. that those farms with successful reproductive management progr ams will have less economic incentive to pursue reproductive management changes. When indivi dual farms asses the potential economic benefit by changing the reproductive management pro gram, the prior level of performance is a key determinant factor Farms that have experienced success with visual estrus detection, as measured by high levels of efficiency in detecting cows in estrus, for example, are more likely to find that the expected net present value of the vis ual estrus detection program remains greater than that of the potential benefit of a synchroniza tion programs considering more labor cost scenarios than farms that have not experienced such a success. The program costs for visual estrus detection and Ovsynch for first-lactation an imals, assuming a group size of 100, across labor costs ranging from $6.00 to $20.00/h is shown in figure 2-2. The cutoff criterion that they used for the programs was that the cow was bred for 6 AI. Specifically, Figure 2.2 shows a comparison of the value of an AI submission rate of 65% achieved with 2.15 labor h/d with the same program valued when using 2.6 labor h/d for vi sual estrus detection programs. The breeding periods assumed was a 21-d period for visu al estrus detection and a 26-d period for synchronization. The difference between the expecte d net present value for the 2 visual estrus detection programs highlights the difference that l abor efficiency has when selecting an estrus detection program. The scenario in which a 65% AI s ubmission rate is obtained in 2.15-labor h/d
42 exhibits greater levels of labor efficiency in dete cting estrus events than one using 2.6-labor h/d to attain the same 65% AI submission rate. Addition ally, Ovsynch scenarios in which a 30% CR is achieved per injection times of 2.1 or 6.3 min a re provided for comparison. Similarly, time for injections affects the total labor costs associated with the program, although the same injections are administered whether it takes 2.1 or 6.3 min/sh ot. In Figure 2.2, it is apparent that the visual estrus detection programs, which use a great deal o f labor, have higher net present value at low labor costs, whereas the Ovsynch program has higher net present value at high labor costs. When looking at the visual estrus detection program, in which a 65% AI submission rate is achieved with 2.15 labor h/d, the visual estrus detection pr ogram yields a greater net present value than Ovsynch with injections taking 2.1 min, if labor co sts are less than approximately $17.50/h. If injections for Ovsynch take 6.3 min, however, the v isual estrus detection program remains the better value program when labor costs are less than approximately $28.00/h. When looking at the visual estrus detection program in which an AI subm ission rate of 65% is achieved with 2.6 labor h/d, the labor costs at which Ovsynch becomes the b etter value program are lower than in the previous case, in which only 2.15 labor h/d were us ed to achieve the same AI submission rate. In the case of 2.6 labor h/d being used to obtain a 65 % AI submission rate, the visual estrus detection program is the better value program when labor costs are less than approximately $14.00 and $20.00/h for Ovsynch with injections tak ing 2.1 and 6.3 min, respectively. Bull Aspects Use of Bulls as Natural Service in U.S.A Although, AI has been recognized as the preferred m ethod to breed cows since its commercial development in the 1950s (Vishawanah, 20 03) a significant number of dairy producers use NS for their breeding program.
43 Champagne et al. (2002), in a survey of bull manage ment practices in California, reported that 84% of the producers reported use of NS at lea st as a component of their breeding program. In addition, this survey identified that the most c ommon use of NS was after unsuccessful AI attempts. Two studies conducted in the Northeast r egion of the U.S.A. reported that the use of NS as component of dairy farms breeding program var ies from 55% to 74% (NAHMS, 2002; Smith et al. 2004). In a study that compared pregn ancy rates (PR) between AI and NS in Georgia and Florida dairy herds, the use of NS alon e or in combination with AI was reported to be around 70% (de Vries et al. 2005). Caraviello et al. (2006) reported in a survey that examined management practices in 103 herds participating in the Alta Genetics (Watertown WI) Advantage Progeny Testing Program. The dairy producers aimed to capture the genetics b enefits of AI, howeved 43% of herds used a clean-up bull. Furthermore, Caraviello indicated th at in average non-pregnant cows were moved to the clean-up pen after 6 unsuccessful AIs or 23 2 d post partum. Bull Behavior, Evaluation and Factors Affecting Fer tility Anderson (1945) differentiated sexual behavior in the bull into two components: libido (or sex drive) and ability to copulate (or mating abili ty). Libido has been defined as the willingness and eagerness to mount and complete service of a fe male and mating ability as the ability to complete service (Hultnas, 1959). Mating behavior i s that behavior exhibited immediately before, during, and after service (Chenoweth, 1981) Both libido and mating ability are important in bulls, and there is ample evidence tha t these two traits are influenced strongly by genetic factors (Bane, 1954 and Blockey et al., 197 8). Deficiencies in these traits represent major causes of bull wastage (Signoret, 1980 and Rawson, 1959). Rawson (1959) also reported that the basic pattern of male sexual behavior in cattle appears to be innate in that animals reared in comp lete isolation often will exhibit normal mating
44 behavior when exposed to a female in estrus. Howeve r, Chenoweth (1981) described that rearing young postpuberal males in all-bachelor groups may delay or inhibit subsequent expression of heterosexual mating behavior. Although libido is be lieved to be influenced largely by genetic factors, mating ability has a learning component th at could be influenced by rearing methods. The degree of error that this learning factor impos es upon the assessment of libido in young bulls has varied in different studies from negligible to significant (Aenelt et al., 1958; Chenoweth, 1979 and Osborne et al. 1971). Young male calves of ten display aspects of sexual behavior during play. The most common behave is the jumping impulse (Bonadonna, 1944). This impulse is not, however, sex-limited as it also is seen in females under steroid influences and in castrated males. In the intact bull, this behavior gradually develops into coordinated mating behavior under the mediation of nervous and hormonal influen ces (Galloway, 1970). In the bull, different indicators have been used to identify puberty, including ejaculation of the first viable spermatozoa and ejaculation of the first semen sample containing a minimum of 50 x 106 spermatozoa with at least 10% showing progressive motility (Wolf et al., 1965). These definitions do not describe development of sexual b ehavior, which often does not reach full proficiency until some time after the spermatogenic definitions of puberty are achieved. When both spermatogenic and behavioral components are de veloped adequately for natural procreation, full puberty (or sexual maturity) is a chieved. Breed differences occur in the time required for development of both components and in the time relationship between them (Chenoweth, 1979). Social interactions between animals often have been differentiated into amicable and agonistic categories. Amicable behavior is seen mos t commonly in young animals with a stable dominance hierarchy and is expressed by such action s as sham fighting and bunting, mounting,
45 and licking of the head, neck, and preputial region s (Blockey, 1975)). Agonistic behavior is more evident in older animals during the formation or re establishment of the social order and includes all those activities associated with conflict (Scot t, 1956). Social hierarchies are established quickly (within 10 to 60 min) in animals placed sud denly together in a group, and such hierarchies are more prominent with animals that ha ve had considerable experience with such encounters (generally older animals) than in those, which have not (Hafez and Boissou, 1975). Changes occur in social behavior, as bulls get olde r. With dairy bulls, agonistic behavior greatly increases when they reach 3.5 to 4.5 yr of age (Kilgour and Campin, 1973). Although, horns and physical size may influence achievement o f dominance of an individual within a group of bulls, age and seniority within the group appear to be of greatest importance in mixed-age groups (Blockey, 1975 and Chenoweth, 1979). Chenoweth et al. (1993) revised the breeding soundn ess evaluation used by the majority of veterinarians worldwide. The two pages that summari zed the guidelines are at the end of this chapter (Figures 2-3 and 2-4). Chenoweths model fo r breeding soundness evaluation was published at the proceedings for annual meeting fro m Society for Theriogenology in San Antonio, Texas after 3 years of discussion for new guidelines. This revised guideline by Chenoweth et al. (1993) replaced the breeding sound ness evaluation by Bierchwal, (1976) incorporating important findings of current researc h at the time that made this guideline more appropriate. Parkinson et al. (2004) in a review about evaluatio n of fertility and infertility in natural service bulls points out that in essence the breedi ng potential of a bull can be considered to depend upon both its ability to mate and its abilit y to fertilize. Breeding soundness evaluation allows field assessments of a bulls ability to mat e, its libido and of its physical capability to
46 mount, achieve intromission, ejaculate and quality of the semen that the bull produces, which is, in turn, related to physical characteristics of its genitalia. Although it is relatively easy to asses s such traits in the field, their value as predictors of bulls fertility remains the subject of considerable debate. Bull management can severely affect bull fertility. Macmillan (1998) reported that bull: cow ratio can be underestimated if PR to AI were wo rse than expected. This would result in overuse of bulls, a situation that is not uncommon amongst dairy farms in Australia and New Zealand, where the AI period is short and the breed ing season is highly compact. Other management factor that plays an important rol e is the period length of exposure of bulls to dairy cows. One strategy suggested to impr ove the libido and performance of NS sires as well as reduce the risk of lameness is a rotational management system (Overton et al., 2003). This management system involves maintaining two gro ups of bulls on the dairy farms, at all times. One set is considered as the working group and is commingled with lactating cows. The second set is held in reserve and is referred t o as the resting group. The two groups are rotated every 14 week. Among all parameters used to evaluate breeding soun dness, scrotal circumference is emphasized because it is a good indicator of sperm output. Testis size is correlated highly with daily sperm output, since sperm production per unit of testis volume is a constant figure. Thus, sperm output is primarily determined by the size of the testes; a figure which is easily ascertained in the live bull by measurement of the scrotal circ umference (Almquist et al., 1976; Coulter and Keller, 1982). Measuring scrotal circumference is particularly imp ortant in the examination of yearling bulls (Brinks, 1994), since it is a good indicator of whether the animal is pubertal. Puberty occurs
47 when scrotal circumference is between 28 and 30 cm, 52% of bulls are pubertal when their scrotal circumference has reached 28 cm and 97% by the time it is 30 cm (Spitzer and Hopkins, 1997). The major factors affecting the age at which the testis reaches these threshold values are the genetic and nutritional effects which determine the rate of testicular growth, but age or breed per se are relatively unimportant (Spitzer and Hopk ins, 1997). Consequently, the American Society of Theriogenologists (Hopkins and Spitzer, 1997) recommends that all breeding bulls should have a minimum scrotal circumference of 30 c m. Kasari et al. (1996) demur slightly from this opinion, suggesting that slightly higher figur es (3233 cm) should be used in breeds such as the Simmental, Angus and Maine-Anjou. Whether it is correct to increase the minimum acceptable testis size for some breeds is open to d ebate, it is the clear opinion of Hopkins and Spitzer (1997) that no figure lower than 30 cm shou ld be allowed, even for breeds that are of smaller stature. Testis size (and, hence, scrotal circumference) con tinues to increase after puberty, so the scrotal circumference of bulls that are 2 years old should exceed 3334 cm (Coulter, 1991; Hopkins and Spitzer, 1997). Changes in testis size after 2 years of age are breed-dependent (Chenoweth et al. 1984). Scrotal circumference has also been related to seme n quality parameters such as number of sperm, percentage of motile sperm and percentage of morphologically normal sperm (Coulter and Foote, 1979; Jakubiec, 1983; Gipson et al., 198 7; Madrid et al., 1988; Chacon et al., 1999). Consequently, many reports have demonstrated that s crotal circumference is positively related to conception and/or pregnancy rates (e.g. Mateos et a l., 1978; Makarechian and Farid, 1985; Coulter and Kozub, 1989; McCosker et al., 1989). Ho wever, a number of other reports call into question the relationship between scrotal circumfer ence, semen quality and fertility
48 (Makarechian et al., 1983; Raadsma et al., 1983; Lu nstra, 1985; Williams, 1988; McGowan et al., 2002). Holroyd et al. (2002) also noted that b reeding soundness traits were correlated poorly with fertility. Furthermore, Thompson and Johnson ( 1995) failed to find a relationship between scrotal circumference and calving interval. Some of the discrepancies between results can be explained with reference to the populations of anim als that were examined. Coulter and Kozub (1989), for example, found that whilst scrotal circ umference of mixed age bulls was related to fertility, within each individual year-group there was no relationship. Only when data across year-groups were pooled (thereby increasing the ran ge of values) the effect of scrotal circumference on fertility became signicant. Never theless, it may be that the relationship is based upon probability of normality rather than a d irect correlation, since bulls with low scrotal circumference are less likely to have normal semen quality or fertility than bulls with a normal circumference (Cates, 1975; Smith et al., 1981). On the other hand, low scrotal circumference is not completely inimical to adequate semen quality o r fertility, nor is it guaranteed by high circumference. Scrotal circumference can also be af fected by the fatness of the bull (Barth, 1997), further confounding its relationship with fe rtility. Moreover, even in the studies that have shown a relationship between scrotal circumference and fertility, the relationship may be too imprecise to allow the prediction of actual pregnan cy rates. Coulter and Kozub (1989) incorporated scrotal circu mference into a multi-factorial predictor for fertility; yet even when factors such as libido and bull:cow ratio were also included, the model was unable to accurately predict fertilit y outcomes. Likewise, even though Makarechian and Farid (1985) were able to relate sc rotal circumference to fertility, the relationship between the two was not strong enough to be predictive of achieved pregnancy rates.
49 On the other hand, scrotal circumference is highly heritable (Coulter et al., 1987; Gipson et al., 1987; Graser and Raznozik, 1992; and see Brink s, 1994), and is related both to age of puberty of male and female progeny (Brinks et al., 1978; Lunstra et al., 1978; Smith et al., 1989; Brinks, 1994; Moser et al., 1996) and to subsequent fertility of female progeny (Jakubiec, 1983; Werre and Binks, 1986). Hence, advantages would acc umulate from selecting bulls of higherthan-average scrotal circumference, even if it were unrelated to the fertility of the bulls themselves. Despite all the controversial findings regarding br eeding soundness evaluation and fertility, Alexander (2008) reported that breeding soundness e valuation has been well accepted by the veterinary profession and the cattle industry as a standard for determining if a bull is a good potential breeder and is a satisfactory method of i dentifying subfertile breeders. Kastelic and Thundathil (2008) reported that tradit ional breeding soundness evaluation would usually identify bulls that are grossly abnor mal. However, a comprehensive approach, including assessing sperm function and fertility at the molecular, cellular and whole-animal levels, is needed to predict fertility of bulls tha t are producing apparently normal sperm. Kastelic and Thundathil et al. (1999) discussed several fact ors that can be involved with the prediction of fertility such as: sperm plasma membrane, sperm mot ility, sperm-oviduct interaction, sperm capacitation, sperm zona pellucida interaction, spe rm oolema fusion and sperm DNA decondensation. Semen Quality Semen quality standards for natural service sires m irror in general accepted ideas about minimum thresholds that have to be attained if a bu ll has an acceptable fertility (Parkinson et al., 2004). Minimum of 30% motility, 70% normal sperm a nd age-dependent minimal scrotal circumference probably represent a consensus of opi nion over the standards that are acceptable
50 to veterinary andrologists. Using such criteria, bu lls that fail a breeding soundness evaluation generally have more sperm abnormalities than those who pass (Spitzer et al., 1988), largely as a result of the strong emphasis that is placed upon m otility/morphology in the evaluation process (Higdon et al., 2000). It is a fact that the relati onship between semen quality and fertility is contradictory, although many authors have reported that percentages of morphologically normal or abnormal sperm are related to conception rate (J aczewski and Kazimirow, 1997; Aguilar, 1978; Chenoweth, 1980b; Coulter and Kozub, 1989; Pa ngewar and Sharma, 1989; Larsen et al., 1990; Gotschall and Mattos, 1997; Fitzpatrick et al ., 2002; Padrik and Jaakma, 2002; Holroyd et al., 2002). The signicance of initial motility of the ejaculate is less clear, with some reports (Aguilar, 1978; Chenoweth, 1980b; Pangewar and Shar ma, 1989; Gotschall and Mattos, 1997) nding that it is related to fertility, others (Fit zpatrick et al., 2002; Holroyd et al., 2002) did no t report a relationship between semen quality and fer tility. On the other hand, there are reports that none of the commonly assessed parameters of semen q uality are reliably or consistently related to fertility (Smith et al., 1981; Lunstra, 1985; Ma karechian et al., 1985; Makarechian and Berg, 1988). Despite these latter ndings, many bulls tha t are presented for infertility examination have abnormalities of semen that can explain their poor results (Dirks, 1983), so examination of semen is obviously an essential component of a bree ding soundness examination. Sperm Pathologies Sperm abnormalities have traditionally been classi ed by site (head, tail, midpiece, cytoplasmic droplets) or site of origin (primary: t estis; secondary: epididymis; tertiary: accessory glands/post ejaculation). Blom (1983) advanced unde rstanding of the signicance of sperm abnormalities by classifying them according to thei r effect on fertility into major and minor defects. Major defects include most abnormalities o f the head and midpiece, proximal cytoplasmic droplets and single abnormalities that are present in a high percentage. Minor
51 defects include looped tails, detached sperm heads and distal cytoplasmic droplets. More recently, the signicance of specic sperm abnormal ities has become better understood from the results of mating trials, analysis of non-return ra tes to articial insemination and in vitro fertilization with semen with high percentages of s perm with individual classes of abnormalities. In particular, the notion of compensable and uncomp ensable abnormalities has been developed from such studies (Saacke et al., 1988). Barth (199 7) described the two forms of abnormalities; abnormal sperm which are not transported to the ute rine tube, or which are unable to penetrate the oocyte can be compensated by increasing sperm d ose. Such defects are therefore compensable. Sperm cells, which are capable of pe netrating the zona, but they fail to cause cleavage or result in non-viable embryos, cannot be compensated by increasing sperm dose. These defects are therefore uncompensable. Research is still required to elucidate how these categories relate to classical sperm morphology ass essments. However, some abnormalities, such as chromatin defects are unequivocally uncompensabl e (Evenson, 1999; Saacke et al., 2000) and other abnormalities (as discussed below) have effec ts in vitro fertilization systems that indicate that they are also likely to be uncompensable. Head abnormality of sperm The head of the sperm consists of the genetic mater ial (in the form of highly condensed chromosomes) and key effectors of fertilization (i. e. binding and passage through the zona pellucida). Hence, most abnormalities of the head a re associated with a signicant impairment of fertility (Wilmington, 1981; Soderquist et al., 199 1). Abnormal condensation of chromatin (Johnson, 1997) and abnormal nuclear shape (Osterme ier et al., 2000, 2001) are closely associated with reduced fertility. Many defects of the head can be observed through careful examination of simple eosinnigrosin stained smears although some require special stains or phasecontrast microscopy to be detected.
52 The most common defect, the pyriform (pear shape) h ead, is readily recognizable through the narrow, elongated appearance of the head and th e pinching in of its post-acrosomal region. The defect commonly appears as an acquired defect d uring testicular degeneration. Fertility is affected by the degree of deformity of the sperm he ad (Petac and Kosec, 1989), probably as a consequence of a reduction of its total surface are a (Barth et al., 1992). Nothling and Arndt (1995) described that a bull with 36% pyriform head s achieved a 46% pregnancy rate (versus 75% for a normal bull). This abnormality impairs bo th fertilization rate and subsequent embryonic development (Thundathil et al., 1999), wi th failure of cleavage being the main problem. Some bulls normally produce spermatozoa th at are relatively pyriform in shape and, as a consequence, can be relatively subfertile. Acrosomal defects are also associated with reduced fertility. Of these, the knobbed acrosome defect is best known. It can be difficult to observe (Barth and Oko, 1989), yet the present author has found it relatively easy to dete ct in carefully made eosinnigrosin smears. It is a common incidental nding at low percentages, but can occur at high percentages (25100%; Barth, 1986) as a familial, or, in the case of the Friesian, inherited defect. Moderate percentages of abnormal sperm are associated with reduced CR (A ndersson et al., 1990), but bulls with high percentages are virtually sterile. Thundathil et al (2000) used sperm with knobbed acrosome defects for in vitro fertilization, nding that no sperm with the defect penetrated the zona pellucida and that embryos that were fertilized by normal sperm from affected bulls had a slower rate of cleavage than those from control bul ls. Nuclear vacuoles are the most difficult of the head abnormalities to visualize in eosin nigrosin smears, but can usually be seen in wet pre parations or with phase contrast microscopy. The best known is the diadem defect, which is seen as a series of refractile lesions at the base of
53 the acrosome. Other vacuoles can appear as single o r multiple lesions of the nucleus. It is common to observe occasional sperm with vacuoles in normal semen, but bulls with a high percentage of vacuolated sperm are severely inferti le or sterile (Miller et al., 1982; Saacke et al., 1995). Some vacuoles are undetectable by light micr oscopy, but can be found by electron microscopy in bulls with unexplained low fertility (Barth and Oko, 1989; Parkinson et al., 1993). Non-specic acrosomal abnormalities are variably as sociated with reduced fertility; for example, Meyer and Barth (2001) found that bulls wi th high percentages of abnormal acrosomes achieved normal CR except in competitive mating tri als. Other acrosomal defects were classied by Blom (1983) as major defects, reflecting the rel atively large effects that they have upon fertility. Midpiece and tail abnormalities of Sperm Detached heads occur commonly at low to moderate pe rcentages in normal ejaculates and are only associated with infertility if present at high percentages. The abnormality was classied as minor by Blom (1983) and the presence of 3040% of detached heads in an ejaculate is not associated with infertility (Johnson, 1997). Howeve r, a rather more serious defect occurs in the Hereford, Guernsey and Brown Swiss breeds (Blom and Birch-Anderson, 1970; Blom, 1977a; Kozumplik, 1990), in which nearly 100% of sperm are decapitated. Interestingly, the detached tails are motile, so the gross motility of the seme n appears normal to a cursory examination. This defect is probably inherited. Similarly, the tailstump defect, in which morphologically normal heads are attached to a vestigial structure which a ppears like a protoplasmic droplet, occurs as an inherited condition of several breeds of bull (see Blom, 1976; Blom and Birch-Anderson, 1980). On electron microscopy, this droplet-like st ructure can be seen to consist of small segments of flagellar material, which represent a v estigial tail that if present will make bulls sterile.
54 Defects of the midpiece and tail generally arise as defects of spermatogenesis, and sperm with such abnormalities are either non-motile or ha ve subnormal motility (Barth and Oko, 1989). Consequently, the presence of such abnormalities is generally associated with subfertility (Blom, 1983). It is also common to find sperm with gross d eformities of the tail and midpiece in association with a wide range of other abnormalitie s (i.e. abnormal heads, detached heads, proximal droplets, etc.) in animals that are suffer ing from testicular degeneration (Parkinson, 1987, 2001). It is rare for the coiled tail to occu r at high percentage, but the apparently-similar Dag defect, in which the tail appears as a loose co il, occurs at low to moderate percentages as an acquired defect, or at high percentage (50100%) as an inherited defect of the Jersey (Barth, 1997). Bulls with a high percentage of Dag defects are either sterile or of very low fertility (Blom, 1966). The distal midpiece reex abnormality resembles a looped tail with a droplet enclosed within the loop. It has little e ect upon fertility in AI, but causes subfertility i n natural service sires (Barth, 1992; Johnson, 1997). The sim ple looped tail (i.e. with no enclosed droplet) is generally regarded as a tertiary (post ejaculati on) defect, which arises when sperm are subjected to osmotic or temperature shock. The defe ct can also be present when the pH of seminal plasma is abnormal (e.g. in animals with se minal vesiculitis), or in the company of mixed abnormalities in animals with testicular dege neration. Abaxial implantation of the tail is no longer regarded as a signicant abnormality, sin ce it does not affect fertility (Barth, 1989; Pant et al., 2002). The presence of accessory tails is not signicant at low percentage, however when present at high percentage cause infertility ( Williams and Savage, 1925). Gossypol appears to exert unique and selective effe cts upon the male reproductive system, which includes reduced spermatogenesis and sperm mo tility, associated with morphological aberrations of the sperm midpiece (Chenoweth et al. 1994). Risco et al. (1993) reported an
55 increase in midpiece abnormality and erythrocyte fr agility in Brahman bulls fed 2.75 kg day-1 of cottonseed meal (8.2 g day-1 of free gossypol). Chase et al. (1994) reported a s imilar damage to seminiferous epithelium for Brahman bulls fed eithe r 1.8g day-1 of free gossypol from cottonseed meal or 16 g day-1 of free gossypol from whole cottonseed indicating t hat the type of cottonseed product (whole versus meal) might play a fundamenta l role in toxicological effect of gossypol. It has been suggested that detoxification of gossypol in the rumen is more efficient with whole cottonseed that with cottonseed meal. Cytoplasmic droplets of Sperm Spermatozoa are released from the seminiferous epit helium with their residual cytoplasm in the form of a droplet just behind the head (prox imal droplet). During passage of the epididymis, the droplet rst migrates to the distal end of the midpiece (distal droplet), and then is lost entirely during sperm maturation (Rao et al., 1980). Distal cytoplasmic droplets are not generally regarded as serious abnormalities (Blom, 1983; Johnson, 1997). Although they can occur at high percentages in animals with defects o f sperm maturation, such as epididymal dysfunction, or, more commonly in young bulls and o veruse (Barth, 1997). On the other hand, proximal droplets are a more serious abnormality, u sually regarded as a defect of spermatogenesis (Johnson, 1997), especially where t hey occur with other, mixed, abnormalities. When proximal droplets are present at signicant pe rcentages, substantial impairment of fertility results. For example, Blom (1977b) suggested that e jaculates containing as little as 510% of proximal droplets are associated with poor fertilit y, whilst Nothling and Arndt (1995) showed that a bull with a high percentage of proximal drop lets achieved a low pregnancy rate in a mating trial. Likewise, Soderquist et al. (1991) and Saack e et al. (1995) showed that the proportion of sperm with proximal droplets is related to nonretur n rate to AI and to pregnancy rate in superovulated heifers, respectively. Furthermore, w hen sperm with proximal droplets have been
56 used in vitro fertlization, cleavage rates of embry os are poor (Amann et al., 2000). Proximal droplets are, however, common in the rst few ejacu lates from peri-pubertal bulls. Several studies have shown that immature bulls have high pe rcentages of proximal droplets in the peripubertal period, but that these rapidly decline to normal levels thereafter (Evans et al., 1995; Johnson et al., 1998; Arteaga et al., 2001; Padrik and Jaakma, 2002). Most older bulls display low (but quite repeatable) percentages of proximal droplets (Soderquist et al., 1996), and the mean percentages of affected sperm increases during warmer seasons of the year (Sekoni and Gustafsson, 1987). Where a high proportion of proxi mal droplets occur in mature bulls (often with other, mixed, abnormalities) it reflects a per turbation of the spermatogenesis process. Venereal Diseases in Bulls Venereal diseases in bulls cause reproductive wasta ge and result in enormous economic losses to the dairy industry. Among the venereal di seases reported in the United Sates campylobacteriosis and trichomonosis are the most p revalent and most significant venereal causes of reproductive loss (Ball et al. 1987). In both, losses are caused by infertility, embryonic death, and abortions due to salpingitis, endometrit is, and cervicitis. (Parsonson et al. 1976 and Roberts, 1986). Campylobacteriosis and trichomonosis are nearly ide ntical in their clinical presentation in dairy cows, however their control is completely dif ferent. Control of either, as with other diseases, must includes attempts to stop transmissi on, eliminate the infection in affected animals, and prevent reintroduction of the organism (Abbit a nd Ball, 1978. Abbit, 1980 and Abbit, 1981). Although epidemiologic aspects are similar for the two diseases, control of campylobacteriosis is easier because effective vaccines are available. There are commercially available vaccines that are effective for the control of Campylobacteriosis that should be used as the princ ipal method of prevention and control in
57 bull-bred herds (Ball et al., 1987). It is importan t to emphasize that vaccines are only effective if used according to label directions. In general, vac cines adjuvinated with modified Freunds (oil) adjuvant give better immunity (Vasquez et al., 1983 ). Trichomonosis must be controlled by considering epi demiological aspects of its transmission. Trichomonosis is caused by the proto zoan parasite, Tritrichomonas foetus The bovine disease is characterized by pregnancy loss, usually early and occult, although abortions of fetuses up to 7 months gestation have been reporte d (Abbitt, 1980; Fitzgerald, 1986; Skirrow, 1987; BonDurant and Honigberg, 1994; BonDurant, 199 7, 2005). It is highly prevalent in naturally bred cattle; in California, an estimated 16% of beef herds are infected (BonDurant et al., 1990) and infection in dairy herds that use bu lls is not uncommon (Goodger and Skirrow, 1986). A larger survey of Florida beef cattle repor ted a herd prevalence of 30.4% (Crews et al., 2000). The disease is insidious in that neither infected c ows nor bulls show overt signs but tremendous economic losses are realized due to the reduction in calving rate following a herd infection (Rae, 1989). Estimates of the national co st of bovine trichomoniasis, based on limited prevalence surveys and market prices of more than 1 5 years ago, range as high as $600 million or more (Speer and White, 1991). Only one species of the bovine pathogen is describe d (Honigberg, 1978). In cattle, the organism is considered an obligate parasite of the reproductive tract (BonDurant, 1997), so transmission to the female is presumed to occur sol ely during coitus with an infected bull (Goodger and Skirrow, 1986). Trichomonad organisms live on the epithelium and th e epithelial crypts of the gland penis and prepuce of bulls (Ball et al., 1984 and Porsons on el al. 1974). Since these crypts develop as
58 the bull ages, the habitat for trichomonads probabl y is more favorable in older bulls (Samuelson, 1966). Several authors reported episodes where you ng bulls of most breeds have been found sporadically infected and bulls older than two year s are persistent carriers (Abbit and Meyerholz, 1979, Christensen et al., 1986, Clark et al., 1974 and Kimsey et al., 1980). Thousands of trichomonads are required for a consistently infect ive dose (Clark et al. 1974). Under heavy breeding pressure, the population of trichomonads o n the penis of carrier bulls may be depleted to the extent that some cows do not receive an infe ctive dose when they are bred, but when carrier bulls are under reduced breeding pressure t ransmission is likely to approach 100 per cent (Clark et al., 1983). Some old and most young bulls are resistant to infe ction with Tritrichomonas foetus. However, even resistant bulls may mechanically tran smit trichomoniasis by first breeding an infected and then susceptible female within 20 to 3 0 minutes (Clark et al., 1977). Mechanical transmission of trichomonads does not occur natural ly between cows by means other than venereal disease and thus does not occur when infec ted cow are not in estrus. Artificial mechanical transmission can occur under some condit ions (Goodger and Skirrow, 1986). Risk of chronic (often life-long) trichomonosis inf ection in the bull increases with age (Abbitt, 1980; Fitzgerald, 1986; Skirrow and BonDur ant, 1988; BonDurant et al., 1990; BonDurant, 2005) contrast, yearling bulls are relat ively resistant to chronic infection with true T. foetus. Even though trichomonosis is thought to be only transmitted sexually, several studies have reported trichomonad isolations from virgin bu lls (BonDurant et al., 1999; Hayes et al., 2003; Grahn et al., 2005). Trichomonads infections are usually self-limiting i n the cow, and very few infected cows maintain the infection throughout gestation. Cows t hat do carry the organism through gestation
59 may have the ability to infect susceptible bulls du ring the subsequent breeding period (Bartlett, 1947, Bartlett and Dickmans, 1949 and BonDurant, 19 85). Nevertheless, most cows that have calved normally are not infected. Therefore, with a dequate management the impact of occasional carrier cow on reproduction should be small (Ball e t al., 1987). After initial infection, cows are convalescent for approximately 3 months and then become temporarily immune to T. fetus. Most immune cows can be reinfected after approximately 1 year, but the subsequent convalesce nt period is only about 3 weeks long (Clark et al., 1974). Consequently, infection confers a de gree of immunity and resistance that can be advantageous in some management schemes. Campylobacteriosis is caused by Campylobacter fetus subspecies venerealis and is an infectious cause of infertility in cattle that is s pread venerealy by asymptomatically infected bulls. Infection of cows can result in a uterine en vironment unsuitable for embryo implantation, leading to early embryonic loss (Ware 1980). Exposure of bulls positive for Trichomonosis to a l arge proportion of an uninfected herd inevitably results in a marked decrease in pregnanc y rate, approximately 20% of cows becoming pregnant in a mating period of 60 days (Carroll and Hoerlein 1972). Chronically infected herds may show suboptimal reproductive performance in sub sequent years caused by transmission of infection to susceptible young stock entering the h erd (Hoerlein et al. 1964). The average pregnancy rate in such herds varies fro m year to year depending on the relative proportions of carrier, susceptible and im mune breeding-age females, and of infected and non-infected bulls within the herd (Carroll and Hoe rlein 1972).
60 Ball et al. (1987) reported that the most satisfact ory way to control Trichomoniasis should be based on a stringent surveillance program of bot h bulls and cows and then to cull positive animals. Comparison of Natural Service and Artificial Insemi nation In the U.S.A., the combination of natural service a nd AI is the preferred breeding method in 43% to 84% of dairy producers (Caraviello et al 2006; NAHMS 2002, de Vries et al. 2005, Smith et al. 2004 and Champagne et al. 2002). Although, these producers understand the benefits o f AI, they also recognize that detection of estrus in order to inseminate cows is inefficien t because not all cows are identified in estrus due to: human errors, attenuated expression of estr us in high producing cows, and adverse responses to heat stress. Therefore, producers th at use NS maintain that more cows are bred by NS compared to AI because human errors in estrus de tection are avoided when bulls are used. The most common method for NS use is to comingle bu lls with lactating cows and thus allow bulls to assume the role of both estrus detector an d inseminator. This reduces perceived labor costs and eliminates human errors associated with e strus detection. Despite the popular use of natural service in dairy farms there has been limit ed research on the economics of this breeding program. A study by Hillers et al. (1982) utilized systems a nalysis to study costs and returns of breeding dairy cows artificially or by natural serv ice. In their analysis, semen cost, estrus detection cost, days open, and bull maintenance cos ts were included. In addition, genetic merit of sires, discount rates on expected returns, and prob ability of a female offspring reaching lactation were also included. Transmission of genetic advanta ge of sires used by artificial insemination over sires used by natural service to both daughter and granddaughter was considered. Daughters of sires used for artificial insemination were superior to daughters of natural service
61 sires by 227, 454, or 682 kg (mature equivalent) mi lk for a necessary calving interval of 374, 384 and 394, respectively. Breeding was started 60 days into lactation and continued for 15 cycles (21 days each) or until 90% of the cows would be ex pected to have conceived. Conception rate from artificial service was decreased by 5% of tota l rate for the subsequent breeding. For comparing artificial insemination and natural servi ce, an initial conception rate for artificial insemination of 50%, cost of keeping a bull of $15 per cow per year, semen cost of $8 per unit, costs for detection of estrus of $10 per cow per ye ar, discount rate of 10%, a 40% chance of obtaining a lactating heifer replacement per concep tion, a cost of an additional day open of $1.50, and income over feed costs of $.099 per kg w ere applied. Calving interval was 365 days for breeding by natural service. Each increase in g enetic advantage superiority of bulls used artificially over natural service bulls of 227 kg m eant that the longer calving interval obtained with AI days longer resulted in the with the same e xpected returns. Other factors in the analysis had less effect on the comparison of artificial ins emination with natural service than the genetic abilities of sires. Investment in herd health (repr oductive) programs to increase breeding efficiency appeared economically sound. Johnston et al. (1987) calculated the annual cost a ssociated with maintaining a single herd sire for 22.5 years in a 40-cow Wisconsin dairy. K eeping a NS sire for breeding management costs US$ 22.03 per cow in 1987, which was less exp ensive than using AI, but the study did not consider the value of the genetic differences betwe en the herd sire and AI sires. Shaw and Dobson (2000) assessed the impact of a cha nge from standard bull breeding to on-farm do-it-yourself AI in small dairies in the U nited Kingdom during a period of three years. According to their work, the cost of using natural service sires was approximately 76% of the cost of the on-farm AI program, once all of the cas h costs were considered. However, by the
62 second and third year, the AI program was more pro table due to the improved reproductive efficiency that resulted in increased milk producti on and more calves. These differences in cost and protability were reported without any evaluati on in potential benet from genetic improvement that was likely in the AI program. Overton (2004) estimated the explicit and implicit costs of natural service and AI including loss of genetic progress associated with the use of natural service sires in dairy herds. Overton used a partial budget approach to stochastically mo del the expected costs and returns of reproductive management options in large, western, Holstein dairies. Option one was comparison of natural service sires managed using currently re commended methods including breeding soundness evaluations, bull vaccination, and a rota tional breeding system. Option two was an AI system using a modied Presync-Ovsynch timed AI pro gram in conjunction with estrus detection and inseminations performed by a commercial route b reeder. Stochastic variables in the model included the cost of the lactating ration and purch ased bulls, as well as the value received for milk, market bulls, and net merit gains. All other variables were treated deterministically. Under his models assumptions, the use of natural service sires averaged approximately US$ 10 more in cost per cow per year when compared to the AI progr am. Sixty percent of the time, AI was less expensive than using bulls. However, there was a wi de variation in expected differences in cost between the two systems with net merit estimates ha ving the largest impact, followed by prices received for milk sold and market bulls. Valergakis et al. (2007) compared the costs associa ted with breeding cattle by do-ityourself AI and NS in dairy farming conditions in G reece. A simulation study was designed based on data from 120 dairy cattle farms that diff ered in size (range 40 to 285 cows) and milk production level (4000 to 9300kg per cow per year). Different scenarios were employed to
63 estimate costs associated directly with AI and NS a s well as potentially extended calving intervals due to AI. Results showed that bull maint enance costs for NS were 1440 to 1670 per year (US$1,820 to US$2,111). Direct AI costs were h igher than those for NS for farms with more than 30 cows and extended calving interval con stituted a considerable additional inconvenience. In fact, amongst the factors that af fected the amount of milk needed to cover total extra AI costs, number of days open was the dominan t one. Semen, feed and heifer prices had a very small effect. Hypothetically, use of NS bulls resulted in a calving interval of 12 months; AI daughters with a calving interval of 13.5 months ha ve to produce about 705kg of additional milk in order to cover the extra cost. Their actual milk production, however, exceeds this limit by more than 25%. When real calving intervals were con sidered (13.0 v. 13.7 months for NS and AI, respectively) AI daughters turn out to produce more than twice the additional amount of milk needed. Valergakis concluded that even under less t han average management conditions, AI is more protable than the best NS scenario. Reproductive performance of natural service versus AI has not been evaluated extensively. The first report comparing the aspects of fertility of cows bred by natural service or AI was by Elving and Govers (1975), where the difference betw een the non-return percentage (60-90 days) following 17,086 first inseminations and after 9,77 6 first natural matings in Dutch-Friesian cattle was studied in a random sample of the Netherlands H erd Book records in 1969. The effects of the following factors on this difference in the cas es studied were considered: age of bulls and cows, frequency of natural service and artificial i nsemination during each estrus, use of deepfrozen semem, housing and grazing periods. After co rrections of the difference for these factors, it was estimated that no more than 9 per cent of no n-return 60-90 days in favor of natural service.
64 Williamson et al. (1978) used information routinely supplied during the conduct of a dairy herd health program to evaluate the performance of artificial breeding in Victoria province Australia. A comparison was made between 60 to 90-d ay non-return rates (supplied by artificial breeding centers) and pregnancy rates (determined b y manual pregnancy diagnosis) for first artificial inseminations in 108 herd years in which both responses were available in the 1973 and 1974 breeding seasons. The values were 69.3% and 58 .2% respectively (P <0.001). Non-return rates and CR were found to decline as herd size inc reased. Pregnancy rates to first artificial and natural services did not differ significantly from each other, but pregnancy rates were significantly more variable to natural than artific ial service (P < 0.001). The mean pregnancy rate to artificial insemination for all herd years studi ed was 57.5% and the pregnancy rate to natural service was 58.0%. De Vries et al. (2005) evaluated the effects of art icial insemination and natural service breeding systems on pregnancy rates by stage of lac tation, season, and changes in milk production over time using lactation and herd DHIA records of Holstein cows in dairy herds located in Florida and Georgia. The reported geneti c prole of service sires of the herd was used to determine the percentage of cows bred to natural service bulls (%NS). Two seasons were considered: winter (NovemberApril) and summer (May October) from 1995 to 2002 (16 periods). Herd-periods were assigned 1 of 3 breeding sy stems: AI (0 to 10% NS), mixed (11 to 89% NS) and NS (90 to 100% NS). Seventy percent of the herds used NS bulls as a component of their breeding system during the study period. The PR during winter (17.9%) was greater than that during summer (9.0%). During winter, PR for AI herds (17.9%) did not differ from that for mixed (17.8%) and NS herds (18.0%). During summer, PR for AI herds (8.1%) was slightly less than that for mixed (9.3%) and NS herds (9.8%). Dur ing winter, PR for cows at 71 to 91 d, 92 to
65 112 d, and 113 to 133 d in milk were 1.4% lower for mixed herds compared with AI and NS. Pregnancy rate for NS herds was 2.6% lower during l ate lactation compared with AI and mixed herds. During summer, PR for cows at 71 to 91 and 9 2 to 112 days in milk were 2.6% and 1.8% greater, respectively, for NS herds compared with A I. However, from 260 to 364 d in milk, PR for NS herds was lower than that for AI and mixed h erds. No signicant interaction was detected between breeding system and lactation number. Rolli ng herd average milk production during the study period was lower in the NS herds (7180 kg) th an mixed AI plus NS herds. However, the annual change in milk production over the seven yea r study period was not different among breeding systems. The results indicated that use of NS bulls did not result in meaningful disadvantages in terms of PR and changes in milk pr oduction overtime. Overton and Sischo (2005) compared the calving to c onception intervals for cows in AI pens with cows exposed to natural service sires, co ntrolling for milk production, mastitis occurrence, parity and calving month effects. Recor ds from ten western U.S.A. dairy herds (mean herd size = 2058 cows) were evaluated retrosp ectively over an 18-month period. Eight bull breeding analysis cohorts were created (the r st cohort 050 days in milk and the remaining cohorts at 25 days in milk intervals through 226 da ys). The cohorts contained non-pregnant cows that were rst moved into bullpens during the descr ibed cohort period. Equal numbers of nonpregnant cows only exposed to AI during the cohort period were selected randomly from the pool of eligible non-pregnant cows. An AI cow was u sed only once in the data analysis but was included in a bull breeding cohort at a later date if she remained non-pregnant and was transferred to a bullpen. Cows in AI groups had hig her hazard rates for pregnancy across all cohorts. Parity and milk production were signicant ly associated with risk for pregnancy resulting in decrease days to pregnancy. Overton an d Sischo (2005) concluded that herds that
66 practice a combination of AI and bull breeding, ove rall herd reproductive performance might be improved by allowing cows more AI opportunities pri or to moving them into the clean-up bullpens.
67 Table 2-1. Criteria for determination of the stage of the estrous cycle, or presence of ovarian cysts or anestrus based on ultrasonography and per rectum palpation of the genital tract (These criteria were adapted from Zemjanis, 1 962; Pierson and Ginther, 1984 and 1987) Stage Clinical Findings Ovaries Uterus Diestrus Functional CL, follicle > 10 mm Slight ton us Metestrus Corpus hemorrhagicum, follicle < 10 mm Ed ema and moderate tonus Proestrus/Estrus Follicle ~18 mm, regressing CL Hig h tonus Ovarian cysts Multiple follicles ~18 mm, absence of CL Flaccid Anestrus Follicle < 18 mm Flaccid (Adapted from Bartolome et al., resynchronization o f ovulation and timed insemination in lactating dairy cows use of the ovsynch and heatsyn ch protocols after non-pregnancy diagnosis by ultrasonography. 2005.Theriogenology 63: page 16 20).
68 Figure 2-1. Depicts the continuity and interaction of events occurring during the estrous cycle in cows with substantial detail of variation of hormon es involved. (Adapted from Moore and Thatcher, Major advances with reproduction of d airy cattle. 2006. Journal of Dairy Science. 89:page 1255)
69 Figure 2-2. Net present values (NPV) of reproducti ve management programs for first-lactation cattle. CR = conception rate (Adapted from Olynk an d Wolf, 2008 Analysis of Reproductive Management Strategies on US Commercial Dairy Farms. Journal of Dairy Science. 91:4088)
70 Figure 2-3. First page of guidelines established b y the Society for Theriogenology for breeding soundness evaluation in bulls. Chenoweth, P.J. 1992 A new bull breeding soundness evaluation form. Society for Theriogenology. In Pro c. Annual Meeting, August 1415, San Antonio, Texas, page. 69)
71 Figure 2-4. Second page of guidelines established by the Society for Theriogenology for breeding soundness evaluation in bulls. Chenoweth, P.J. 1992. A new bull breeding soundness evaluation form. Society for Theriogenolo gy. In Proc. Annual Meeting, August 14-15, San Antonio, Texas, page 70).
72 CHAPTER 3 COMPARISON OF REPRODUCTIVE PERFORMANCE IN LACTATING DAIRY COWS BRED BY NATURAL SERVICE OR TIMED ARTIFICIAL INSEMIA NTION Introduction Despite considerable advantages for AI, a significa nt number of dairy producers use natural service ( NS ) for their breeding program. In a survey on bull m anagement practices in California, 84% of the producers reported use of NS as a component of their breeding program (Champagne et al., 2002). The most common use of NS was after unsuccessful AI attempts. Several studies have compared reproductive performa nce between AI and NS breeding systems. Pregnancy rates (PR) obtained from dairy h erd records of cows bred by AI or NS were not different (Niles et al., 2002; Williamson et al ., 1978), but PR from NS were more variable in NS herds (deVries et al., 2005). A breeding program that synchronizes ovulation and AI at a fixed time (timed AI; TAI) has been developed which allows for 100% of the cow s to be submitted to AI, without the need for estrous detection (Pursley et al., 1995). There have been ample studies that have clearly demonstrated an advantage in pregnancy rate of TAI over insemination at detected estrus (Pursley et al., 1997a; Pursley et al., 1997b; Cart mill et al., 2001). However, studies that compare reproductive performance between NS and TAI, two br eeding systems where efficiency of estrous detection is not a factor, are lacking. It was hypothesized that the use of TAI would result in a greater 21-d cycle pregnancy rate than NS beca use in TAI, cows undergo ovulation synchronization and all eligible cows are inseminat ed at a fixed time. Therefore, the objective of this study was to compare reproductive performance of lactating dairy cows bred by TAI or NS, two breeding system in which estrous detection is n ot required.
73 Materials and Methods Animals, Housing and Diets The University of Florida Institutional Animal Care and Use Committee approved all procedures involving cows and bulls. The study was conducted between November 2006 and March 2008 in a commercial dairy farm of 2,200 Hols tein cows located in north central Florida. Cows were housed in free-stall barns with fans and sprinklers for forced evaporative cooling during the warm season. A total of four barns (2 T AI; 2 NS) each with a maximum capacity of 180 cows were used in the study. These barns were s imilar in design, size, and number of animals housed and were switched between and within seasons to avoid environmental bias. Resting bulls were housed in bermudagrass pasture l ots with portable shades and trees for heat abatement. Lactating cow diets were formulated using the CPM-Dairy cattle ration analyzer (Cornell-Pen-Miner Ver. 3.0.7a) to meet or exceed t he nutrient requirements established by NRC (2001) for lactating Holstein cows weighing 650 kg, consuming 24 kg of DM per d, and producing 45 kg/d of milk containing 3.5% fat and 3 .1% true protein during the first 80 d of lactation. The composition of the diets consisted of corn silage, alfalfa hay, ground corn, citrus pulp, cottonseed hulls, expeller soybean meal (SoyP lus, West Central Soy, Ralston, IA) and solvent extracted soybean meal. Bulls were fed the lactating cow diet during the 2 wk cow exposure period and lactating cow diet weigh back t hat averaged 17.2 kg of DM per bull per d during the 2 wk rest period. Study Design, Treatments and Exclusion Criteria Lactating Holstein dairy cows were blocked by parit y (primiparous and multiparous) and within each block randomly allocated at 42 3 d po st partum into two groups, TAI (n=543) and NS (n = 512), once a week until completion of the s tudy. Prior to study enrollment cows underwent a reproductive tract examination and heal th record evaluation. Cows with uterine
74 infection or adhesion, a displaced abomasum, c-sect ion or fetotomy, and cows that missed any part of their experimental protocol were not includ ed in the study. After enrollment cows that were sold or died or missed any part of their proto col were removed from the study. Eighty nine cows from the TAI group and 118 cows from NS cows w ere removed accordingly. Timed Artificial Insemination Reproductive Manageme nt Cows in the TAI group were presynchronized with 2 i njections of PGF2 (500 g cloprostenol sodium; Estroplan, Pfizer Animal Health, New York, NY) given at 42 3 and 56 3 d post partum. Fourteen d after the second inje ction of PGF2 cows were given an injection of GnRH (100 g gonadorelin; Fertagyl, Intervet Inc, Millsboro, DE) followed 7 d later b y an injection of PGF2, and a second injection of GnRH 56 h after the las t dose of PGF2. The TAI was performed 16 h after the second injection of Gn RH. Eighteen d after TAI, cows received a controlled internal drug-releasing insert (CIDR Eaz i-Breed; Pfizer Animal Health; New York, NY) followed by insert removal and GnRH administrat ion 7 d later, on d 25 after TAI. Cows were evaluated for pregnancy by ultrasonography exa mination at 32 d after TAI. The reproductive program for TAI cows is illustrated in figures 3-1 and 3-2. The presence of an embryo with a heartbeat was the criterion used to d etermine pregnancy as previously described (Ginther, 1998). The re-synchronization chosen aime d to maximize reproductive efficiency and to allow cows to be re-inseminated immediately afte r the diagnosis of non-pregnancy. Based on ovarian dynamics at 18 d after AI, a pre-ovulatory follicle is potentially present and insertion of a CIDR device will maintain this follicle and not all ow ovulation in cows with a regressed CL. When GnRH is administered 7 d later, at CIDR insert removal (d 25 after insemination in TAI cows), ovulation of the follicle is expected and a new follicular wave initiated. Therefore, cows found nonpregnant at 32 d after AI would be ready to receive PGF2 and complete the modified Ovsynch protocol at 35 d from their previous breedi ng. In this manner, the modified Ovsynch
75 protocol begins 7 d before the diagnosis of non-pre gnancy, which shortens the interval between inseminations. Cows diagnosed pregnant were re-examined by transre ctal palpation of the uterus and its contents 28 d later (i.e., 60 d gestation) to recon firm pregnancy status and to identify pregnancy loss. Cows diagnosed not pregnant at 32 d after TAI were administered PGF2, followed with an injection of GnRH at 56 h after PGF2 and TAI was performed 16 h after GnRH. Non pregnant cows were re-synchronized again with the same TAI p rotocol until diagnosed pregnant or at a maximum of 223 d post partum. Natural Service Reproductive Management Cows in the NS group received PGF2 at d 42 3 and 56 3 and were moved to a bull pe n at 70 3 d post partum. Cows were moved to the bu ll pen 14 d after the last PGF2 (70 3 d post partum) to improve synchronized estrus and to have the bull breeding at around 80 d post partum, i.e. similar to the first service in the TA I group. After 42 d of being exposed to the bulls, cows underwent an ultrasonography and trans rectal examination to determine pregnancy status. This allowed a diagnosable gestation length in preg nant cows to vary from 28 to 42 d. The reproductive program for NS cows is illustrated at figures 3-1 and 3-2. Gestation age was estimated by measurement of embryo size, presence o f a heartbeat by ultrasound (Ginther, 1998), and the diameter of the pregnant uterine horn and l ength of the amniotic vesicle by transrectal palpation (Zemjanis, 1970). Gestation age from 28 to 34 d was determined by ultrasound, from 35 to 56 d by ultrasound in combination with transr ectal palpation. Cows diagnosed non pregnant were re-examined for pr egnancy status by ultrasound 28 d later to detect pregnancy in cows that were less th an 28 d of gestation at the previous ultrasound diagnosis (i.e. 28 to 56 d pregnant), utilizing the same criteria described above for ultrasound and transrectal palpation. This procedure was similar f or subsequent groups assigned weekly to the
76 NS up to 223 d post partum. Cows diagnosed pregnant were re-confirmed 28 d later to identify pregnancy loss. The bull to cow ratio in the NS her ds was one bull per 20 non-pregnant cows. Day post partum when pregnancy occurred in NS bred cows was calculated by subtracting the d of pregnancy from the d post partum when pregnancy was diagnosed. For example, a cow diagnosed pregnant 32 d at 130 d post partum was pr egnant at 98 d post partum (i.e. 130 to 32 d). The interval between services in the timed AI group was 35 d due to the process of carrying out the re-synchronization protocol. Therefore, for cow s in the TAI group, d post partum when pregnancy occurred to first, second, third, fourth or fifth service were classified as follows: d 80 3, first service; d 115 3, second service; d 15 0 3, third service; 185 3 d, fourth service, and 220 3 d fifth service. For cows in the NS gr oup, when pregnancy was diagnosed from 28 to 56 d, first, second, third, fourth, fifth, sixth seventh or eighth services were classified at d 7 0 to 90, d 91 to 111, d 112 to 132, d 133 to 153, d 1 54 to 174, d 175 to 195, d 196 to 216 and d 217 to 223 post partum, respectively. A cow in the NS g roup diagnosed 40 d pregnant at 150 d post partum would have conceived at 110 d (i.e. 150 40 d) post partum or at her second service. Pregnancy Loss Because of the reproductive management schemes, NS cows were at different stages of gestation when pregnancy was diagnosed compared to TAI cows, which were consistently diagnosed pregnant at 32 d. Consequently, stage of gestation when pregnancy was diagnosed in the NS group was categorized by 4 d intervals (28 t o 32, 33 to 36, 37 to 40, 41 to 44, 45 to 48, 49 to 52 and 53 to 56) in an attempt to discern the ef fect of embryonic age on pregnancy loss. Bull Management Twenty-six bulls 18-months old at the beginning of the study were used. All bulls underwent a breeding soundness evaluation according to the guidelines of the Society for Theriogenology (Chenoweth, 1992) before cow exposur e. In addition, bulls were tested for
77 Tritrichomonas foetus using a smegma sample cultured in a modified diamo nd media (InPouchTM TF, Biomed Diagnostics, White City, OR). Both of t hese tests were performed every 3 mo for a total of five evaluations for each bull. All bulls were rested for 14 d after 14 d of cow exposure. The breeding soundness evaluation include d a physical examination, testicular evaluation, measurement of scrotal circumference an d evaluation of sperm morphology and motility following electro ejaculation. Only bulls classified as potential satisfactory breeders were used. This classification requires: a minimum of 31 cm for scrotal circumference for bulls between 15 to 18 mo of age; a minimum of individual sperm motility of 30%; and 70% normal spermatozoa. In addition, the bulls were tested for bovine viral diarrhea by imunohistochemistry of skin using an ear notch sample. All bulls were v accinated according to farm operational practices for infectious bovine rhinotracheitis, bo vine viral diarrhea, parainfluenza 3, bovine respiratory syncytial virus, leptospirosis, clostri dial diseases, and campylobacteriosis. Milk Production Data and Body Condition Score Milk weights were recorded once a month for 988 cow s (n = 484 and n = 504 for NS and TAI, respectively). First measurements occurred at different d after calving for the first monthly sample depending upon d of parturition and d of the monthly milk test for cow and herd, respectively. Because cows were randomly assigned t o the treatments on a weekly basis, the first d post partum measurement was balanced between grou ps. Data for the first 3 mo of lactation were obtained from the Dairy Herd Improvement assoc iation (Raleigh, NC). Cows in both the NS and TAI groups underwent a BCS evaluation at 70 3 d post partum before introduction to the bulls in NS or receiving the GnRH injection in TAI using a scale of 1 to 5 according to Ferguson et al. (1994).
78 Temperature Humidity Index The temperature (F) and relative humidity (%) data were obtained fro m the Florida Automated Weather Network (http://fawn.ifas.ufl.edu /scripts/reportrequest.asp). The data were collected from January 2007 to March 2008. The weat her station is located in Alachua, FL, approximately 30 miles from the experimental locati on. Average daily temperature humidity index ( THI ) was calculated as described by West (1993): THI = temperature ( F) [0.55 (0.55 x relative humidity)] x (temperature 58). The THI was the criterion used to determine effect of season (warm or cold) on reproductive performance. The maximum daily THI was categorized as cool, when THI < 72, or warm when THI > 72. The THI on the d of the first TAI or the first d of exposure to bulls was used in the statistical an alysis. Blood Sampling and Evaluation of Cyclicity Blood samples (~6 mL) were collected from a subset of 608 cows (NS = 302 and TAI = 306) before the second PGF2 of the presynchronization program and again 9 d later, which corresponded to 56 3 and 65 3 d post partum. Sa mpling was collected by puncture of the median coccygeal vein or artery using evacuated tub es containing K2 EDTA for plasma separation (Becton Dickinson, Franklin Lakes, NJ). Samples were placed immediately in ice and transported to the laboratory within 5 h of collect ion. Blood tubes were centrifuged at 1,500 g for 15 min, and plasma frozen at 25C until analys is. Analysis of progesterone in plasma was determined using a solid phase radioimmunoassay (Co at-A-Count, Progesterone In-vitro Diagnostic Test Kit, Diagnostic Products Corporatio n, Los Angeles, CA). Plasma concentrations of progesterone of known values were used in duplic ates in every assay to calculate interand intra assay coefficients of variation. The known sa mples were plasma from an ovariectomized cow (0.7 ng/mL), a low progesterone sample (1.0 ng/ mL) and high progesterone sample (5.0 ng/mL. The interand intra-assay CV were 5.74% and 11.1%, respectively. Cows were reported
79 as cyclic if they had progesterone plasma concentra tion equal to or greater than 1.0 ng/mL in at least one of the two samples or non-cyclic if both samples were below 1.0 ng/mL. Health Disorder Monitoring Program and Treatments Farm personnel were trained and farm operational pr ocedures were created by the herd veterinarian (corresponding author) to provide a re liable source for health monitoring and prompt treatment. All cows underwent a post partum health monitoring program consisting of daily evaluation of rectal temperature and attitude from d 2 to 10 pp. Rectal temperature was determined with the use of a digital thermometer (G LA M500HPDT, Agricultural Electronics, San Luis Obispo, CA) between 0700 to 0900 h after m ilking. Retained placenta was defined as the presence of fetal membranes 24 h after calving. Cows that either appeared sick (inappetence, depressed, sunken and/or tented eyes) or had a rect al temperature 39.4oC were examined for vaginal discharge, urine ketones, displacement of a bomasum, and respiratory disorder. The criterion for diagnosis of metritis was the presenc e of a watery, brown, fetid discharge from the vulva (i.e., noted after palpation per rectum of th e uterus) with rectal temperature 39.4oC. Urine was evaluated for ketonuria using urine test strips (KetostixTM, Bayer Diagnostics, Tarrytown, NY). Clinical ketosis was characterized by inappetence, depressed attitude and presence of ketonuria according to the degree of co lor change in the test strips. Cows were examined for clinical mastitis by herd personnel du ring each milking. A case of mastitis was characterized by either the presence of abnormal mi lk or by signs of inflammation in one or more quarters or by both situations. Respiratory disorde r was categorized by the presence of abnormal lung sounds, cough, increased respiratory rate, dec reased milk production and fever. Cows were examined for clinical lameness on a weekly basis as they walked out of the milking parlor to barns. Cows affected with lameness exhibited an arc hed back posture while standing and walking and an abnormal gait. Lame cows were examin ed on a tilt table for lesions and treatment
80 by a professional hoof trimmer. Morbidity was defin ed as the occurrence of at least one health disorder in the first 70 d post partum. Statistical Analysis The outcomes for comparison of reproductive perform ance between NS and TAI were the proportion of cows pregnant in the first 21 d of br eeding, 21-d cycle pregnancy rate, daily rate of pregnancy in the first 223 d post partum, median d non pregnant, and proportion of pregnant cows at 223 d post partum. In order to evaluate th e 21-d cycle pregnancy rate in both NS and TAI cows, an assumption was made that cows were eli gible to be bred every 21 d in both groups, despite the fact that TAI cows had a breeding oppor tunity only every 35 d. Therefore a breeding eligibility period was considered every 21 d up to 223 d post partum for both groups. The proportions of pregnant cows during the first 2 1 d of breeding and at the end of 223 d post partum were analyzed by logistic regression us ing the PROC LOGISTIC of SAS. The model included the effects of group (NS vs. TAI), p arity (primiparous vs. multiparous), BCS categorized as < 2.75 or > 2.75, season of breeding (warm vs. cool) morbidity, and interactions of group with parity, BCS, season of breeding and m orbidity. Modeling was performed using backward stepwise selection with the significance l evel of stay when < 0.10. The model fit statistics were performed by comparison of the diff erence in the deviances by the likelihood-ratio statistic test. Adjusted odd ratio (AOR) and 95% co nfidence intervals (CI) were calculated. The 21-d cycle pregnancy rate was analyzed using th e GLIMMIX procedure for generalized linear mixed models from SAS (SAS/STAT, ver. 9.1, SAS Institute Inc.). The model included the effects of group, parity, BCS, season of breeding, and morbidity. The rate of pregnancy in the first 223 d post partum (daily pre gnancy rate) and median d non pregnant were analyzed using Coxs proportional hazards regression model (PROC PHREG) and the Kapla n Meyer survival curves (PROC LIFETEST) of SAS. The C oxs model included effects of group,
81 parity, BCS categorized, season of breeding, morbid ity, and the interactions of group and season of breeding, and group and morbidity. When interact ions were non significant (P > 0.10), they were dropped from the model. The adjusted hazard ra tios (AHR) and the 95% CI were calculated. In order to determine the impact of milk yield in t he first 3 mo post partum on reproductive performance of dairy cows, additional analyses were performed with 988 cows that had milk yield data of the 1055 cows in the study. The model s were the same described above, but included milk yield either as a continuous variable or categorized into quartiles within primiparous and multiparous cows. Cows d at risk was calculated as the cumulative num ber of d for cows between exposure to bulls and pregnancy or end of study in NS, and betw een first AI and pregnancy or end of study for the TAI group. The proportion of NS and TAI bre d cows affected by health disorders were analyzed by chi-square. Pregnancy loss was analyzed by chi-square analysis using SAS, and it was categorized accordingly with the age of the emb ryo at the time pregnancy was diagnosed. Differences with P < 0.05 were considered significant, and those with 0 .05 < P < 0.10 were considered a tendency. Results Assessment of Bulls Six bulls (23.1%; 6/26) were culled during the stud y: two became lame, one developed a bad temperament, one had a positive test for T. foetus and two were classified as unsatisfactory potential breeders at the completion of the breedin g soundness evaluation. Reproductive Performance The proportion of pregnant cows in the first 21 d o f breeding did not differ (P = 0.17) between groups (Table 3-1). The overall 21-d cycle pregnancy rate, which included a total of 8
82 and 5 service opportunities for NS and TAI, respect ively, was not different between groups and they were 25.7 and 25.0 % for NS and TAI, respectiv ely as shown in table 3-2. However, the rate of pregnancy differed (P = 0.05) between groups and was 15% greater (AHR = 1.15; 95% CI = 1.00 to 1.31) for NS than TAI (Figure 3-3.). The me dian and mean d to pregnancy for NS bred cows were, respectively, 111 (95% CI = 105 to 126) and 131.5 2.3 d, and for TAI cows 116 (95% CI = 115 to 118) and 137.9 2.9 d, respective ly. The survival curves did not differ until 150 d post partum, when they began to separate. To reinforce this observation, an additional survival analysis was performed for the interval to pregnancy up to 150 d postpartum, in which time non-pregnant cows were censored. In the latter scenario, group did not influence (P = 0.44) the rate of pregnancy (AHR = 1.06; 95% CI = 0.91 to 1.23). Nevertheless, at 223 d post partum, which was the end point of the study, the proportio n of pregnant was greater (P = 0.001) for NS than for TAI (NS = 84.8% and TAI = 76.4%). Cow d at risk for pregnancy was not different between NS and TAI, and they were 30,978 and 29,424 d, respectively. Parity, Body Condition Score and Milk Production Parity did not (P = 0.15) affect the proportion of cows pregnant in the first 21 d of breeding. However, a greater proportion (P < 0.001) of primiparous cows were pregnant at the end of 223 d of breeding than multiparous cows (87. 7 vs. 77.8%) because primiparous cows had a 27% greater (P = 0.002) daily pregnancy rate than multiparous cows (AHR = 1.27; 95% CI = 1.09 to 1.48) showing in figure 3-4. At 70 3 d post partum, the distribution among BCS categories was not different (P = 0.66) between TAI and NS: BCS 2.75 were 52.5% for NS and 53.9% for TAI; BCS > 2. 75 were 47.5% for NS and 46.1% for TAI. Cows with BCS greater than 2.75 had increased (P = 0.004) proportion of pregnant cows in the first 21 d of breeding (39.9 vs. 32.4%; AOR = 1.46; 95% CI = 1.26 to 1.89) as shown in figure 3-5 and a lso had an increased (P = 0.02) daily
83 pregnancy rate in the first 223 DIM (AHR = 1.18; 95 % CI = 1.03 to 1.35). Despite those effects, no effect (P = 0.33) of BCS was observed for the ov erall cumulative proportions of pregnant cows at the end of the study which were 78.6% for c ows with BCS 2.75 and 82.4% for cows > 2.75. When additional analyses were performed with the su bset of 988 cows with milk production data, the daily rate of pregnancy tended (P = 0.08) to increase with a concurrent increase in milk yield (AHR = 1.01; 95% CI = 1.00 t o 1.01). At the end of 223 DIM, the proportion of pregnant cows was not (P = 0.23) affe cted by milk production in the first 3 months of lactation. Cyclic Status, Seasonality and Health Disorders Progesterone analyses indicated that 83.1 % (251/30 2) of cows in the NS group and 87.2 % (267/306) of cows in the TAI group were cyclic (pro gesterone > 1ng/mL in at least one sample) before exposure to NS or onset of the TAI protocol. The percentages of cyclic cows were not different (P=0.17) between groups, and cyclic statu s did not affect (P = 0.53) the proportions of pregnant cows in the first 21 d of breeding, which were 35.4% and 38.6% for non-cyclic and cyclic cows respectively. Cows receiving their first breeding during the cool season had increased (P < 0.01) pregnancy in the first 21 d of breeding (41.2 vs. 2 7.7%), 21-d cycle pregnancy rate (27.5 vs. 22.5%), and daily pregnancy rate (AHR = 1.22; 95% C I = 1.06 to 1.41) as shown in table 3-6. It is important to indicate that no interaction betwee n treatment and heat stress was observed for the proportion of cows pregnant in the first 21 d o f breeding or pregnancy rates. The only health disorder that was not (P = 0.03) di stributed equally between TAI and NS was metritis (TAI = 6.6 % and NS = 10.3%). However, metritis did not affect the proportion of pregnant cows in the first 21 d of breeding (Table 3-3.). On the other hand, the proportion of
84 pregnant cows in the first 21 d of breeding was les s in cows with mastitis (P < 0.01), respiratory disorder (P < 0.05), ketosis (P < 0.01), and morbid ity (P < 0.01). Morbidity influenced (P = 0.002) the rate of pregnancy and healthy cows had a 28% greater daily pregnancy rate than cows affected by at least one health problem (AHR = 1.28 ; 95% CI = 1.09 to 1.49) as shown in table 3-7. Pregnancy Loss The overall pregnancy loss considering gestation pe riod from d 28 to 56 in the NS group and 32 d for TAI, was lower (P=0.02) for NS than TA I bred cows, 10.4 % and 15.2%, P <0.05; respectively. However, in the NS group, pregnancy l oss for cows diagnosed pregnant between 28 32 d of gestation was the same as for TAI cows at 32 d of gestation (14.9% and 15.2%, respectively) as shown in table 3-4. Discussion Following the recommendations of the Society for Th eriogenology (Chenoweth, 1992) for breeding soundness, a culling rate of 23.1% occurre d in bulls used in this study. Kastelic el al. (2000) reported that 20 to 40% of bulls from an uns elected population might have reduced fertility. Because these bulls were classified as potential satisfactory breeders prior to cow exposure and were removed from the study and replac ed with sound bulls, the potential for using sub-fertile bulls in the NS group was minimized. De spite the fact that bulls used in this study had repeatedly breeding soundness evaluations (every 3 mo for a total of 5 evaluations) which is more than what is commonly done, our culling rates were not greater than what is expected for service bulls in a random population (Kastelic et a l., 2000). Our approach to bull evaluation and management was chosen to assure that sub-fertile bu lls could be identified rapidly and removed from the herd avoiding a negative impact on reprodu ction.
85 The overall 21-d cycle pregnancy rate in the NS gro up of 25.7% was substantially greater than previously reported by de Vries et al. (2005) in NS herds in the states of Florida and Georgia where 21-d cycle pregnancy rate was 14.0%. Our results can be attributed to the stringent bull management program employed (periodi c resting and breeding soundness evaluation) and early removal of unsound bulls, whi ch reduced the potential for deviation in bull fertility during cow exposure. Cows in the TAI grou p had a first 21d cycle pregnancy rate of 37.4%, similar to a pregnancy rate to first TAI of 37% and 37.9%, reported by Pursley et al. (1997) and Santos et al. (2009), respectively. The greater proportion of pregnant cows observed in the NS group at the end of the study is attribut ed to differences in breeding dynamics between groups. In the NS group, bulls had the potential fo r daily detection of estrus and breeding of nonpregnant cows. On the other hand, due to the TAI re -synchronization scheme, non-pregnant cows in this group required 35 d to be re-inseminated an d thus the number of d to become pregnant increased. However, within this scenario, up to 223 d post partum cows in the TAI group had only five opportunities to be bred compared with a potential eight times for cows in the NS group. The increased median number of d to pregnan cy observed for TAI cows can also be attributed to this difference in breeding opportuni ties. A greater number of non-pregnant cows in the NS group had earlier opportunities to be bred t han TAI cows under the same 21-d cycle pregnancy rate; consequently the final outcome for median time to pregnancy favored the NS group. A greater proportion of pregnant cows and daily pre gnancy rate at 223 d post partum was observed for primiparous cows than multiparous cows This finding indicates that primiparous cows are more fertile than multiparous cows, which agrees with the study of Santos et al. (2009) that reported a greater pregnancy rate to first ser vice in primiparous cows. In the present study a
86 greater proportion of pregnant cows in the first 21 d of breeding was found for cows with a BCS > 2.75 at 70 d post partum. This is in agreement wi th the report by Santos et al. (2009) and Moreira et al. (2000) where BCS around 70 d post pa rtum positively influenced pregnancy rate. Results from the present study support the concept that BCS at 70 d post partum is of paramount importance for the establishment and maintenance of pregnancy in high producing dairy cows. Cyclicity did not affect the proportion of pregnant cows in the first 21 d of breeding in the current study. In contrast, Santos et al. (2009) re ported a greater PR 58 d post AI to first service in cyclic compared to non-cyclic cows. However, in our study the percentage of cyclic cows was greater than expected which diminished sample s ize for a valid comparison between cyclic and non-cyclic cows and likely limits the power to identify an effect of cyclicity in this study. A bull effect also may have occurred in cows bred by NS inducing non-cyclic animals to ovulate. These factors may have contributed to our inability to detect a difference in the proportion of pregnant cows in the first 21 d of breeding between cyclic and non-cyclic cows. Cows bred during the warm season had a lower propor tion of pregnant cows in the first 21 d of breeding in both NS and TAI bred cows. This ag rees with a previous report (De Vries et al., 2005) that showed conception rates of lactating cow s located in Florida decrease to 20% during summer months (June through August). Furthermore, i n the present study pregnancy rate continued to be low during fall (September and Octo ber) when THI decreased. During periods of heat stress (summer), overall PR dropped for cows b red by either AI or NS, but no difference in PR was found between groups. In contrast, de Vries et al. (2005) reported that during summer cows bred by NS had greater 21-d cycle pregnancy ra te than cows bred by AI. However, in the de Vries et al. (2005) study, 21-d cycle pregnancy rate included all cows eligible for AI during summer. The fact that some dairy producers in Flori da choose not to breed cows during summer,
87 may have biased the estimates reported by De Vries et al. (2005). During hot weather, some reduction of bull fertility may be expected due to lowered semen quality associated with an increase in abnormal heads, abnormal acrosome, prox imal droplets and a corresponding decrease in motility (Ott, 1986). In our study, bulls were h oused and managed using heat stress abatement conditions designed for lactating dairy cows (shade fans, evaporative cooling) and changes in bull semen quality may not have occurred or were le ss severe. Therefore, the depression in PR observed during summer in this study with NS and TA I could be attributed to the effect of heat stress on cow fertility. The study herd employed a post partum health monito ring program with the aim to treat disorders promptly. Among the health disorders eval uated, metritis did not affect PR to first service. This result supports the finding by Benzaq uen et al. (2007) who reported that cows with metritis did not have impaired fertility. Our findi ng and those of Benzaquen et al. (2007) reinforced the concept that a post partum health-mo nitoring program, which allows for early diagnosis and treatment of metritis may mitigate im pairment in fertility related to metritis. On the other hand, the proportion of pregnant cows in the first 21 d of breeding was less in cows with mastitis, respiratory disorder, ketosis and mo rbidity. The greater pregnancy loss observed in TAI bred cow s in our study can be attributed to the earlier time of gestation when pregnancy was diagno sed in this group. In a report by Santos et al. (2004) late pregnancy losses were characterized by CL maintenance to the end of the differentiation stage, at approximately 42 d of ges tation, and were more frequent than pregnancy losses after this stage. This pattern of pregnancy loss agrees with our lower pregnancy losses after 40 d of gestation. Therefore, we attribute th e greater pregnancy loss observed in TAI compared to NS bred cows to the d of gestation when diagnosis of pregnancy occurred. Indeed
88 pregnancy loss was the same when compared at compar able stages of pregnancy in the present study. The final logistic regression model revealed that t he variables affecting the proportion of pregnant cows in the first 21 d of breeding were BC S and an interaction between seasonality and morbidity. The effect of BCS on fertility in dairy cows has been well documented previously and possible reasons are clearly described (Domecq et a l., 1997; Lpez-Gatius et al., 2002; Santos et al., 2009). Conclusion The TAI breeding program did not result in a greate r 21-d cycle pregnancy rate compared with NS as initially hypothesized. A greater propor tion of pregnant cows at the end of the study occurred in NS bred cows because they had more oppo rtunities for breeding to occur compared with the TAI reproductive management program. When reproductive performance was compared to the same breeding eligibility period of 21-d cyc le pregnancy rate, there was no difference between NS and TAI. In conclusion, NS and TAI are t wo breeding systems that can be used strategically to minimize problems related to detec tion of estrus, but the extended interinsemination interval in TAI reduces daily pregnanc y rate because these cows have fewer opportunities for breeding. Whether or not TAI is m ore economical than NS warrants investigation.
89 Table 3-1. Reproductive responses in cows bred by natural service (NS) or timed artificial inseminati on (TAI) throughout the study Treatment Variables NS TAI Cows inseminated or exposed to the bulls by 223 DIM 512 543 Proportion of cows pregnant in the 1 st 21 d breeding 34.4% 37.4 Proportion of pregnant by 223 DIM 434 (84.8%) 415 ( 76.4%) Mean d open in pregnant cows ( SEM) 115.9 1.9 113.2 2.0 Median d non-pregnant 111 b 116 a Cow-d at risk 1 30,978 29,424 Pregnancies/1,000 cow-d at risk 14.00 14.10 21-d cycle pregnancy rate, % 2 25.7 25.0 a,b Superscripts in the same row differ (P < 0.05). 1 Cumulative number of d for cows between exposure to the bulls and pregnancy or end of study in NS, and between first service and pregnancy or end of study in TAI. 2 In order to evaluate the 21-d cycle pregnancy rate in both NS and TAI cows, an assumption was made tha t cows were eligible to be bred every 21 d despite the fact that TAI cows had a breeding opportunity only every 35 d.
90 Table 3-2. Pregnancy rates calculated for every 21 -d cycle for cows bred by natural service (NS) or t imed artificial insemination (TAI) throughout the study 21-d cycle number1 Treatment NS TAI ----------% (no./no.) -------------1 st 34.2 (175/512) 37.4 (203/543) 2 nd 24.3 (82/337) 28.7 (97/338) 3 rd 13.9 (35/251) 0.0 (0/241) 4 th 26.8 (56/209) 28.9 (63/218) 5 th 31.1 (47/151) 27.0 (38/141) 6 th 15.8 (16/101) 0.0 (0/117) 7 th 11.8 (10/80) 14.4 (14/97) 8 th 19.4 (13/67) ---Total 2 25.7 (421/1641) 25.0 (417/1669) a,b Superscripts in the same row differ (P < 0.05). 1 In order to evaluate the 21-d cycle pregnancy rate in both NS and TAI cows, an assumption was made th at cows were eligible to be bred every 21 d despite the fact that TAI cows had a breeding opportunity only every 35 d. 2 Data from the 8th 21-d cycle were not included in the analysis.
91 Table 3-3. Effect of health disorders on proportion of pregnant cows in the first 21 d of breeding for cows bred by natural service (NS) or by timed artificial insemination (TAI) Disease Type of disease Yes No P ----------% (no./no.) -------------Metritis a 31.5 (28/89) 35.7 (345/966) 0.49 Lameness 25.6 (11/43) 35.8 (362/1012) 0.19 Retained placenta 28.5 (15/52) 35.7 (358/1003) 0.37 Respiratory 17.2 (5/29) 35.9 (368/1026) <0.05 Mastitis 22.7 (20/88) 36.5 (353/967) <0.01 Ketosis 15.4 (6/39) 36.1 (367/1016) <0.01 Morbidity 26.4 (76/288) 38.7 (297/767) <0.01 a Variable not distributed equally between NS and TAI
92 Table 3-4. Pregnancy losses according to age of ge station at the initial pregnancy diagnosis in cows bred by natural service (NS) or timed artificial insemination (TAI) Treatment Age of pregnancy at first diagnosis (d) Pregnancy l oss (%) TAI 32 15.2 (63/415) a NS 28-56 10.4 (45/434) b 1 28-32 14.9 (18/121) 2 33-36 11.6 (11/95) 3 37-40 14.9 (10/67) 4 41-44 5.3 (2/38) 5 45-48 5.7 (3/53) 6 49-52 0.0(0/11) 7 > 52 2.0(1/49) Total 28-56 12.7 (108/849) a,b Superscripts in the same column differ (P < 0.05). NS
93 Figure 3-1. Timeline of reproductive events to the 1st service, blood sample collection and body score ev aluation for cows enrolled at TAI and NS breeding program
94 Figure 3-2. Timeline of reproductive events for no n-pregnant cows to the 1st service and respective services in TAI and NS bree ding program.
95 50 75 100 125 150 175 200 225 100 80 60 40 20 0 Day postpartumProportion not pregnant NS TAI Figure 3-3. Survival curves for proportion of nonpregnant cows by d post partum for cows bred by nat ural service (NS) or timed artificial insemination (TAI) in the first 223 d po st partum. Median interval to pregnancy for NS and TAI groups were 111 d (95 % CI = 104 to 125) and 116 d (95 % CI = 115 t o 117), respectively. The rate of pregnancy in the 223 d post partum was greater (P = 0.05) for NS than TAI (adjusted ha zard ratio = 1.15; 95% CI = 1.00 to 1.31).
96 Parity and Time to Pregnancy 50 70 90 110 130 150 170 190 210 230 100 80 60 40 20 0 Day postpartumProportion not pregnant (%) Primiparous Multiparous Figure 3-4. Survival curves for proportion of nonpregnant cows by d post partum for primiparous cows and multiparous cows. The hazard for pregnancy in the 223 d post partum was g reater (P = 0.002) for primiparous than in multipar ous cows (adjusted hazard ratio = 1.27; 95% CI = 1.09 to 1.48).
97 BCS and Time to Pregnancy 50 70 90 110 130 150 170 190 210 230 100 80 60 40 20 0 Day postpartumProportion not pregnant (%) < 2.75 > 3.00 Figure 3-5. Survival curves for proportion of nonpregnant cows by d post partum for cows with body c ondition score (BCS) smaller or equal than 2.75 or greater than 3.00. The hazard for pregnancy in the 223 d post partum was greater (P = 0.004) for BCS greater than 3.00 that for BCS smaller or equal tha n 2.75 (adjusted hazard ratio = 1.18; 95% CI = 1.03 to 1.35).
98 Season at First AI and Time to Pregnancy 50 70 90 110 130 150 170 190 210 230 100 80 60 40 20 0 Day postpartumProportion not pregnant (%) Thermoneutral Heat stress Figure 3-6. Survival curves for proportion of nonpregnant cows by d post partum for thermomeutral co ws and heat stress cows. The hazard for pregnancy in the 223 d post partum was g reater (P = 0.01) for thermoneutral than in heat st ressed cows (adjusted hazard ratio = 1.22; 95% CI = 1.06 to 1.41).
99 Morbidity and Time to Pregnancy 50 70 90 110 130 150 170 190 210 230 100 80 60 40 20 0 Day postpartumProportion not pregnant (%) Healthy At least 1 disease event Figure 3-7. Survival curves for proportion of nonpregnant cows by d post partum for healthy cows and cows with the occurrence of at least one event of disease. The hazard for pregn ancy in the 223 d post partum was greater (P < 0.01 ) for healthy cows than in cows with at least one event of disease (ad justed hazard ratio = 1.28; 95% CI = 1.09 to 1.49).
100 CHAPTER4 FINANCIAL ANALYSIS OF DIRECT COMPARISON OF NATURAL SERVICE SIRES AND TIMED ARTIFICIAL INSEMINATION IN A DAIRY HERD Introduction Reproductive efficiency plays a fundamental role in the economic viability of the dairy industry. De Vries (2008) reported that in a U.S.A. herd producing 20,000 lbs of milk, 1 percentage point pregnancy rate (PR) is valued betw een $22 and $35/cow per yr when PR varied from 15 to 19%. Similarly, an extra day open beyond 90 days cost between $1 and $5, with increasing value as the lactation progresses (De Vr ies, 2008). Lack of estrus detection is a major factor that impairs reproductive performance and pr ofitability of lactating dairy cows (Pursley et al., 1997). Timed artificial insemination and the use of natura l service ( NS ) sires are 2 breeding programs that are used to overcome the problem of l ow estrus detection efficiency. Artificial insemination has many advantages such as the elimin ation of venereal diseases, more accurate dry-off dates, reduced incidence of dystocia, incre ased safety for farm employees (Vishwanah, 1993) and greater genetic improvement resulting in daughters that are more productivity and profitable (Norman and Powell, 1992). Nevertheless NS is still a breeding program widely used throughout the US (NAHMS, 2002; Smith et al., 2004; De Vries et al., 2005; and Caraviello et al., 2006). Recently, Lima et al. (chapter 3) compared the repr oductive efficiency of NS and TAI without estrus detection side by side on a large co mmercial dairy farm in Florida. That study showed little differences in reproductive efficienc y. The objective of this study was to compare the costs and profitability of the use of NS sires and TAI in the study of Lima et al. (chapter 3) and provide sensitivity analysis for differences in PR, feed cost, milk prices, semen prices,
101 genetic progress, and opportunity cost of replacing NS sires with additional cows. Materials and Methods The economic analysis was performed using data from the field study comparing NS and TAI as breeding programs from lactating cows that w as conducted in north central Florida between November of 2006 and March of 2008 (Lima et al., Chapter 3). First, costs and revenues of both the NS and TAI program were collected and c alculated. Secondly, differences in profitability due to differences in reproductive ef ficiency were calculated. Finally, a sensitivity analysis was carried out. The data was organized in a spreadsheet (Excel 2007, Microsoft Corporation, Redmond, WA, U.S.A.). Field Study Cows in the field study were housed in free-stall b arns with fans and sprinklers for forced evaporative cooling during the warm season (May to October). Four barns (2 TAI; 2 NS) each with a maximum capacity of 180 cows were used in th is study. Lactating cow diets were fed a diet formulated using the CPM-Dairy cattle ration a nalyzer (Cornell-Pen-Miner Ver. 3.0.7a). After calving, cows were randomly assigned to the N S group or the TAI group. All cows were presynchronized with injections of PG F2 on day 423 and 563 after calving. The price of a dose of PGF2, was $2.03. Pregnancy diagnosis was performed by ultrasound. The cost of a pregnancy diagnosis was $ 3.00. Cows that had a displacement of abomasum, c-section or fetotomy were not included in the study. Cows that missed any part of their proto col were removed from the study. Cows that were found in a pen of the other group (NS or TAI) were also removed from the study. Cows that were sold or died during the study were also exclud ed from the study. Pregnancy rates were determined for each group from the end of the VWP t o 223 d post partum. The overall 21-d
102 pregnancy rates in the field study were 25.7 and 25 .0 % for the NS and TAI groups, respectively. Cows in the NS group were exposed to bulls 14 d aft er estrus presynchronization on day 70 after calving. Each pen of 180 cows was exposed to 5 bulls. Pens included both non-pregnant and pregnant cows. For each bull in a pen with cows there were 1.17 bulls in the resting pen. Therefore, there were 0.028 bulls in breeding pen a nd 0.033 bulls in the resting pen per slot. Pregnancy diagnosis was performed 42 d after first exposure to bulls to determine pregnancy status. Non-pregnant cows in the NS group were re-examined by pregnancy diagnosis every 28 d until diagnosed pregnant or up to 223 d post partum, whichever occurred first. Twenty-six bulls, all 18 mo old at the beginning of the study, were used. After this period of one year the bulls were sold for an average pric e of $1,116.00. Bulls culled prematurely were sold for $670.00. All bulls underwent a breeding soundness evaluation according to the guidelines of the Society for Theriogenology (Chenoweth, 1992) before first exposure to cows. In addition, bulls were tested for Tritrichomonas foetus. The breeding soundness evaluation (BSE) and Tritrichomonas foetus test were performed every 3 months for a total of 5 evaluations for each bull. In addition, the bulls were tested for bovine viral diarrhea by imunohistochemistry of skin using an ear notch sample. All bulls were vaccinate d according to farm operational practices for infectious bovine rhinotracheitis, bovine viral dia rrhea, parainfluenza 3, bovine respiratory syncitial virus, leptospirosis, clostridial disease s, and campylobacteriosis. Each bull was purchased by the amount of $1,148.00 staying for 1 year in the farm. The price of all breeding soundness evaluation plus trichommonosis testing wa s 152.50 per bull entering the herd. All bulls were rested for 14 d after 14 d of cow ex posure. Natural service sires were fed
103 the lactating cow diet during the 2 consecutive wk they were exposed to the cows. An assumption based in previous measurement at the spe cific dairy that bulls intake was 80% of the lactating cows were made. A weigh back lactating cow diet that averaged 17.2 kg of dry matter/bull per d was fed during a 2 wk rest period Resting bulls were housed in Bermuda grass pasture lots with portable shade and trees for heat abatement. The cost of feeding each bull during the exposure and resting periods were calcul ated in $3.30 and $2.37, respectively. Cows in the TAI group enrolled in a modified Ovsync h protocol 14 d after estrus presynchronization. Average VWP for first inseminat ion was 80 d. Non-pregnant cows in the TAI group were re-synchronized with a CIDR inserted 18 d after TAI and removed 7 d later, when GnRH was given. Cows were examined for pregnan cy on d 32 after TAI; non-pregnant cows received PGF2 and GnRH 56 h later followed by TAI 16 h after the GnRH injection (Ovsynch). Non-pregnant cows in TAI group were re-i nseminated up to 5 times using the same scheme before the end of the study (Resynch). The c ost for each dose GnRH was $1.84. The cost of each CIDR device was $8.43. Each dose of semen c ost on $6.00 and labor cost for each insemination was $3.00. Herd Budget Calculator A partial budget was developed to calculate the eco nomic differences between the NS and TAI programs. Economic differences were caused by differences in reproductive costs, VWP, and pregnancy rates. The partial budget consis ted of 3 steps. In the first step, the actual net costs for the NS and TAI group in field study were enumerated per cow entering the experiment (breedin g pool). Because in that study cows entered the breeding pool for 14 months, net costs were adj usted for the number of cows entering the breeding pool per year. This adjustment resulted in reproductive costs per cow per yr (Tables 4-1 and 4-2) for both programs.
104 In the second step, economic differences between bo th programs as a result of differences in VWP and pregnancy rates, but excluding reproduct ive costs, were calculated. A herd budget was developed to calculate the fraction cows by par ity, day since calving and pregnancy status. The time step was 1 day. Inputs and prices were cho sen to match those during the field study as close as possible. Annual risk of forced culling for non-pregnant cows in parities 1 through 4 were set at 18, 28, 38, and 48%, respectively. For pregnant cow s, the annual risk of forced culling was 10%. Daily risk of forced culling was calculated as 1-(1 -annual risk)(1/365). Cows not pregnant after 320 days were culled on day 321. Culled cows were repla ced with calving heifers. The price of a culled cow was set at $400 and the price of a calvi ng heifer was $1,900. All calving heifers were purchased and assume to be the same for both the NS and TAI groups. Cows that got pregnant moved to the next parity aft er gestations of 280 days. The VWP for the NS program was set at 70 d with a daily 4.7 6% service risk. This equals a 100% service risk in a 21-d period. Conception rates were varied to obtain the desired pregnancy rates. Pregnancy rates matched either those in the field s tudy or were varied for sensitivity analyses. For the field study, the conception rate was set at 25.7% to obtain a 25.7% pregnancy rate. The VWP for the TAI group was set at 80 d with 35 days between breeding opportunities, 100% service risk, and 29.3% conception rate. This resul ted in a 25.0% pregnancy rate. Daily milk yield yt for cows in both breeding programs was calculated as yt = a tb exp(-c/1000 t) d where t is the days since calv ing (Wood, 1969). For parity 1, a = 19.00, b = 0.34, and c = 2.80. For parities >1, a = 26.00, b = 0.34, and c = 5.00. Parameter d = 1.156 was a multiplier to obtain a 305 d herd milk yield of clo se to 22,000 lb/cow per yr observed during the field study. Herd milk yield was calculated by mult iplying the daily milk yield by the faction
105 cows on day t. Cows were dry the last 60 days of ge station. The default milk price was set at $20/cwt. Feed cost per cow was set at $1.50 maintenance cost per day and $0.03/lb milk produced. Calf prices were set at $200. The advantage in genetic progress of the TAI progra m was calculated from the lifetime net merit of a TAI breeding (on average $361 in the field study) minus the estimated lifetime net merit of a NS breeding ($163). Assuming the value w ould be expressed 3 yr from the breeding, discounted at 8% interest per year, and lifetime is 3 yr, the annualized advantage of the TAI breeding was (1/(1.08))3 ($361 $163) / 3 = $52. Further, this value app lied only to heifer calves (48%) born from cows (0.75/cow per yr) that were raised and calved themselves (85%). Multiplied, the default genetic advantage of the TA I program was $15.94/cow per yr. Performance of cows in parities >4 were equal to 4th parity cows. The fraction cows in parities >4 was calculated from the fraction cows e ntering the 4th parity and the fraction cows culled in the 4th parity (Handbook for Mathematics page 23). Results were calculated for the steady state situation where herd demographics were constant over time. The herd budget also determined 6 factors that affe cted the reproductive costs. First, the number of cows entering the breeding pool and the n umber of pregnancy checks was calculated for both programs per slot per year. For the TAI pr ogram, the fraction of cows not pregnant after 223 d (the end of the experiment) was calculated. T he TAI costs for eligible cows after 223 d until the end of the breeding period at 320 d after calving were added to the TAI cost per slot per yr. The fraction of calvings from 2nd parity cows was also calculated for the TAI progra m for the evaluation of the economic advantage of genetic progress due to AI. For the NS program, the number of slots per bull was calculated based on th e number of eligible days per cow per yr. The
106 reason is that lower pregnancy rates would require more bulls per slot to maintain the same number of bulls per open cow in the breeding pen. F inally, the feed costs per bull per day were varied with the same magnitude as the marginal feed cost. For example, if marginal feed costs were doubled, then bull feed costs were doubled. In the third step, net revenues per slot per yr wer e calculated as all revenues minus all costs. Revenues consisted of milk sales, calf sales and cull cow sales. Costs consisted of feed cost, replacement costs, and reproductive costs, as show in Table 4-3. Any other costs, such as non-reproductive labor costs, were assumed to be th e same and therefore not included in the analysis. The economic advantage of the TAI program was calculated as the net revenues for the TAI program minus the net revenues for the NS progr am. Sensitivity Analysis Three sets of scenarios were used to investigate th e effects of variations in pregnancy rates, milk price, feed cost, semen cost, genetic a dvantage of TAI breedings, and opportunity cost of replacing bulls with cows. In the first set, inputs from the field study were used with the following exceptions. The semen cost per dose was $2.00, $12.00 or $22.00. Ma rginal feed costs used were $2.00, $5.00 and $8.00/cwt of milk produced. Milk prices were $1 2.00, $18.00 or $24.00/cwt. The genetic advantage of pregnancies generated by TAI compared to NS was $0.00, $300.00 or $600.00. These inputs were varied one by one; with all other inputs the same as for the field study. In the second set of scenarios, the VWP for both br eeding programs was set to 80 d and conception rates adjusted to obtain pregnancy rates of 12%, 18% or 24% for both the TAI and NS breeding programs. Semen cost, marginal feed cos t, milk prices and genetic advantage was varied as in the first set of scenarios. The third set of scenarios evaluated opportunity co sts of a fixed herd size of 1000 slots
107 where bulls replaced 0, 14, or 28 cows. In the fiel d study, 0 cows were replaced. Pregnancy rates were varied as in the second set of scenarios. Results Field Study The herd budget determined the fraction cows enteri ng the breeding pool at 0.9586/slot per yr. The number of pregnancy diagnoses was 4.88/ slot per yr. Costs and revenues of the NS program in the field study are shown in Table 4-1. Cost of the NS program was $163.3/cow per yr which included $71.48 for the purchase of the bu lls, $3.90 for injections of prostaglandin, $28.21 for feeding bulls in the resting pen, $33.46 for feeding bulls exposed to the cows, $2.44 for labor including management of bulls and adminis tration of injections for presynchronization, and $14.64 for pregnancy diagnosis. Revenues consis ted of the sale of bulls at $63.10/cow per yr. Net cost of the NS program was therefore $100.5 3/cow per yr. The fraction cows entering the TAI program was 0.95 36/slot per yr. There were 9.6% more non-pregnant days from the end of the experime nt at d 230 to the end of the breeding period at d 320 after calving. There were 0.75 calv ings/cow per yr in the TAI program from cows starting their 2nd or greater parity. Calves from these calvings had an economic genetic advantage. The number of pregnancy diagnoses was 4. 34/cow per yr for the TAI program. The average number of service per cow per yr was 2.59. Costs and revenues of the TAI program in the field study are shown in Table 4-2. Cost for TAI was $76.32/slot per yr which included $3.90 for injections of prostaglandin for presynchronization, $4.94 for injections of prostag landin in Ovsynch and Resynch, $10.37 for GnRH injections, $20.48 for CIDR inserts, $14.58 for sem en, $2.82 for labor including administration of injections and CIDR insert and re moval, $7.29 for AI labor, and $13.02 for pregnancy diagnosis. The economic value of the gene tic advantage of calves sired by AI was
108 $15.94/slot per yr. Net cost of the TAI program was therefore $61.84/slot per pr. Voluntary waiting periods and PR of the NS and TAI programs were different. The herd budget determined that at the end of the breeding p eriod (320 d after calving), 96% of the cows in the NS program were pregnant and 92% of the cows in the TAI program. Average days to conception were 135 for the NS program and 137 for the TAI program. Consequently, costs and returns caused by differences in herd demographics were different (Table 4-3). The TAI program resulted in greater milk sales, cow sales, replacem ent cost and feed cost. The NS program resulted in greater calf sales. Revenues minus vari able costs and reproductive cost were $2,201.19/slot per yr for the NS program and $2,172 .50/slot per yr for the TAI program. This advantage of $28.69/slot per yr for the NS program was more than offset by the $38.69/slot per yr greater reproductive cost. Net economic advantag e of the TAI program compared to the NS program was therefore $10.00/slot per yr in the fie ld study. Sensitivity Analysis The first set of scenarios revealed large effects o f semen price, marginal feed cost, and genetic advantage on the economic advantage of TAI over NS before adjustment for differences in VWP and pregnancy rates (Table 4-4). One dollar more expensive semen increased the cost of the TAI program by $2.51/cow per yr. One-dollar gre ater marginal feed cost/cwt increased the cost of the NS program by $19.22/cow per yr. One-do llar greater milk price/cwt increased the economic advantage of the TAI program by $1.34/slot per yr. An increased in net merit of $1 decreased the net cost of the TAI program by $0.08/ slot per yr. Table 4-5 shows the economic advantage of the TAI p rogram including adjustment for differences in VWP and pregnancy rates. The differe nce between Table 4-4 and 4-5 for the same set of inputs is the advantage in profit per slot p er yr of the TAI program due to differences in VWP and pregnancy rates. These varied from $23.34 t o $39.38/slot per yr in the advantage of
109 the NS program. The effect of more expensive semen and genetic progress are the same as in Table 4-4 because they only affect the reproductive cost of the TAI program. One-dollar greater milk price/cwt increased the economic advantage of the TAI program by $1.34/slot per yr. Onedollar greater marginal feed cost/cwt increased the cost of the NS program by $19.22/slot per yr. The TAI program more profitable than the NS program for all evaluated inputs when semen price was $2. The NS program was more profitable fo r some inputs when semen price was $12 or greater. The second set of scenarios calculated the effects of variations in PR. Conception rates for the TAI program were set at 0.2840 (24% PR), 0.2286 (18% PR) or 0.1645 (12% PR) depending on the desired PR. Conception rates for the NS prog ram were the same as the desired PR. Voluntary waiting periods were set at 80 d after ca lving but differences remained in the daily probability of pregnancy between both programs caus ed by differences in service rates and conception rates. When PR was set at 24%, 18% or 12% for the NS progr am, the herd budget determined that the number of cows per bull in a breeding pen were 35.2, 28.6, and 22.1. Eligible days per cow per year were 71.6, 88.1, and 114.1, respective ly. The number of pregnancy diagnoses was 4.89, 5.56, and 6.60, respectively. Reproduction co sts were $102.29 (24%), $123.08 (18%), and $155.80 (18%) for the NS program. When PR for the TAI program was set at 24%, 18%, an d 12%, the fraction cows not pregnant after 223 d was 0.135, 0.175, and 0.23.2, respectively. Eligible days per cow per year were 71.1, 87.5, and 113.2, respectively. The numbe r of pregnancy diagnoses per slot per year was 4.38, 4.68, and 5.14, respectively. Reproductio n costs were $64.27 (24% PR), $68.54 (18%), and $75.89 (18%) for the TAI program.
110 Not accounting for differences in PR (Table 4-6), o ne-dollar greater marginal feed cost/cwt increased the cost of the NS program by $21.03/slot per yr when the PR of the NS program was 24%. When the PR of the NS program was set at 18% o r 12%, one-dollar greater marginal feed cost/cwt increased the cost of the NS program by $2 5.89 or $33.53, respectively. For the same pregnancy rates for TAI and NS the pro fit of TAI over NS was consistent independent of use low pregnancy rates as 12% or hi gh pregnancy rates as 24%. The only exception was for the use of semen of $22.00 for pr egnancy rates of 24% that resulted an economic advantage for NS. The same pattern of consistent profit of TAI over N S was observed when pregnancy rates were higher in TAI than in NS in this case with no exception. The profit of TAI over NS for pregnancy rates greater in NS than TAI was inconsis tent. The economic advantage of NS over TAI in scenarios where NS had better reproductive p erformance was offset for greater costs with marginal feed cost and genetic advantage resulting in a profit for TAI over NS. The advantage for different pregnancy rates reporte d in table 4-7 accounted for the different 21-d cycle pregnancy rates obtained at th e study Lima et al. (Chapter 3). If those differences in 21-d cycle pregnancy rates and VWP w ere not accounted the economic of TAI over NS presented in table 6 would be consistently slightly smaller as it is depicted in table 5. However, the outcomes per slot per year would compl etely follow the same trends founds for variation of pregnancy rates per cow per year where difference 21-d cycle pregnancy rates and VWP are not accounted. Those numbers shown were con sistently greater for an assumed same pregnancy rates for NS and TAI or lower pregnancy r ates for TAI than for NS. If the assumed pregnancy rates were greater for TAI than for NS th e economical advantage of TAI was
111 consistently lesser. Nevertheless, it is noticeable that for same pregnancy rates TAI always presented economically advantageous than NS. Opportunity costs are shown in Table 4-8. The oppor tunity cost produced by the replacement of bulls for lactating cows for the rat io of 1 bull per a lactating cow or 0.5 bull per cow lactating at the same pregnancy rates cows gene rated a increase in profit of TAI over NS of $29.41 and $58.82 per slot per year, respectively, for the pregnancy rates obtained in the study. If an pregnancy rates of 12% for both NS and TAI it is assumed, the economic balance of TAI over NS for the replacement of 1 bull per lactating cow or 0.5 per lactating cow was slighter smaller being $26.19 and $52.37 per slot per year. When ext reme low pregnancy rates of 12% were assumed for TAI and good pregnancy rates of 24% wer e assumed for NS the replacement of 1 bull per 1 lactating cow reduced the economic disad vantage in $57.86 per slot per year. Therefore, the replacement of bulls per lactating c ow resulted in consistent considerable economic advantage for TAI independently of the pre gnancy rates. Discussion Cow day at risk for pregnancy were not different be tween NS and TAI, and they were 30,978 and 29,424 days, respectively. Cow day at ri sk was used as input to calculate pregnancy rates in our economical model. In addition, the haz ard for pregnancy was 15% greater for NS due the fact the cows in this breeding program had more opportunities for breeding what resulted in greater proportion of pregnant cows at the end of t he Lima et al. (chapter 3) study. The aims of the current study were to compare the c ost and profitability of natural service (NS) and timed artificial insemination (TAI) two br eeding system that do not require estrus detection as the sole reproductive program on a com mercial dairy farm in random allocated field study. For the best of our knowledge this is the fi rst time that TAI and NS two breeding system that do not require estrus detection are compared e conomically in controlled field trial. Final
112 outcome from this financial analysis show that TAI program was $38.69 per cow per year less expensive than NS. If increased hazard for pregnanc y and earlier VWP for NS breeding program are accounted the economic advantage of TAI is redu ced for $10.00 per slot per year what is similar with values reported by Overton (2005), how ever it is necessary to emphasize that study had model assumptions that did not account for diff erences in pregnancy rates and VWP. Among all the factors that contributed for this economic advantage of TAI the cost of feeding bulls was definitely the major component responsible for this difference. Feeding cost of bulls was 37.8% and 61.6% of total bull costs and net cost for NS, respectively. Similarly, Overton, 2005 reported feeding cost for bulls of 29.8% and 61.2% of total bull costs and net cost for NS, respectively. This important role played for the feeding cost is emphasized and expanded for other magnitude by simulated scenarios where marginal feeding cost increase had consistently the biggest impact in profitability of TAI over NS. Dairy producers ar e probably not familiar with what is the proportion of feeding cost in the accountability of a breeding program, which possibly generates the belief that NS is less expensive than AI or TAI (Overton, 2005). We are aware of that the bulls in this project were manage more intensively than what is normally done in United States, however, this differences are already accounted wit h the greater 21-days cycle pregnancy rates obtained in this study (25.7%) compared to NS 21-da y cycle pregnancy rates reported in natural service of 9.0% in the summer and 18% in the winter respectively. (De Vries et al., 2005). Differences in cost might be offset for different r eproductive performance as was reported by Tenhagen et al. 2004, however as mentioned previous ly this was not problem in our budget, because reproductive performance was taken in consi deration. Simulated scenarios for different pregnancy rates w ith no difference in pregnancy rates for TAI and NS show that the profitability of TAI i s even greater when low pregnancy rates are
113 compared. Possibly cows in those breeding program w ith lower pregnancy rates will take longer to become pregnant and the NS breeding program will require feeding bulls longer, which should add up for the already evident economic benefit of use TAI over NS. Genetic advantage of TAI is also important factor i n this financial analysis, which accounts for 47.1% of the profit of TAI over NS. Th e genetic advantage was also reported by Overton (2005) that point out under his models ass umptions this variable as the main variable driving variation of costs between NS herds and AI herds. This is future foregone income that will be generated by an increased milk production o f heifers genetically superior produced by the use of AI. This is probably a key benefit attribute d for the use of AI and should not be ignored, but if so the profit of TAI over NS still present. The simulated scenarios also follow a pattern of reliable increase of TAI economical advantage over NS for greater genetic advantage. The possibility of replace bulls for lactating cows in the TAI program is other possible foregone income that should be accounted and if is has a significant impact on the profit of TAI over NS per slot per year. Bulls are occupying spac es that potentially could have a lactating cow generating more income for the dairy producers and when this taken in consideration the benefits of TAI are even more evident. This opportunity cost can make the profit of TAI over NS under same pregnancy rates reach high values such as: $12 8.36 of profit when a 1 bull is replaced by 1 cow for pregnancy rates of 12% for TAI and NS. The economic analysis presented in this manuscript was based on the results of the study Lima et al. (2009 chapter 3) where compliance all ow 21-d cycle pregnancy rates that are considerably greater of what is reported in average for U.S.A. dairy herds (Devries et al., 2005) and certainly influenced the efficiency and profita bility of both breeding programs. The herd budget created for this financial analysis permitted accurately to report costs
114 and revenues of both breeding program accounting ev en for differences in 21-d cycle pregnancy rates. The differences in profitability due an incl usion of different 21-d cycle pregnancy rates in the herd budget calculator are in agreement with pr evious reports in the literature. Conclusion Timed artificial insemination resulted in the breed ing program $38.69 less expansive than natural service breeding program per cow per year u nder the conditions of the present study contradicting the belief that the use of bulls is c heaper method of breeding cows to avoid problems with estrus detection. Even when the great er 21-d cycle pregnancy rates and shorter VWP from the Lima et al. (2009 chapter 3) were ac counted, which clearly benefit NS we had TAI economically advantageous than NS. The main var iables that driving for this difference were feeding cost for bulls and genetic advantage o f TAI. The differences in profit were even greater when opportunity cost provided by the repla cement of bulls by lactating cows was taken in consideration. Therefore, TAI is a more economic al option for breeding lactating cows eliminating problems with estrus than NS
115 Table 4-1. Cost and Returns for NS used in the eco nomic analysis NS $/cow/year Costs 1) Purchase of bulls Price per bull = ($1,148.00) Average days bulls staying on the farm per year: 35 4 Total bulls needed entering herd per cow per year: 0.062 Calculation: 0.062 x ($1,148.00) = $71.48 2) Additional expenses (BSE vaccines for bulls, trichomonosis test, other hea lth costs) = $152.50 Calculation: 0.062 x $152.50 $9.50 3) Feed costs (Cows/bull ratio in the breeding pen : 36/1) Bulls in the breeding pen per cow = 0.028 / Bulls i n the resting pen per cow = 0.033 Feed cost per day in the breeding pen = $3.30 / Fee d cost per day in the resting pen = $2.37 Feed cost per bull per year = ($1,021.00) Calculation: 0.028 x ($3.30) + 0.033 x ($2.37) x 365 = $61.67 4) Labor costs (Fixed labor to manage bulls + labor to give presynch injections) Calculation ($2.06 + $0.38) = $2.44 5) Pregnancy check expenses (4.50 times per cow per year at $ 3.0 each) $14.64 6) Prostaglandin cost for pre-synchronization ($2 .035) 2 doses per each cow Percentage of cows entering the breeding program ye ar = 96.4% Calculation: 0.965 x 2 x 2.035 = $3.90 Total costs $163.63 Returns 1) Sale of bulls Percentage of bulls culled prematurely = 23% Sale price for bull culled prematurely = $670.00 Sale price for bull culled healthy = $1,116.00 Total returns = Calculation: 0.23 x 0.062 x 670 + 0.67 x 0.060 x 1116 = $63.10 Net costs for NS = Total returns NS Total costs NS Net costs for NS = $63.10 $163.63 = ($100.53) ** *BSE = Breeding Soundness Evaluation
116 Table 4-2. Cost and Returns for TAI used in the ec onomic analysis $/cow/year Costs 1) Hormone and semen cost Cows entering the breeding program year = 95.4% / C ows non pregnant per year: 11.3% Number of doses per cow per year and cost of Prosta glandin Pre -synchronization: 2 and ($2.035) Number of doses per cow per year and cost of Prosta glandin Ovsynch/Resynch: 2.59 and ($2.035) Number of doses per cow per year and cost of GnRH: 6.01 and ($1.84) Number of inserts per cow per year and cost of CIDR : 2.59 and ($8.43) Number of breeding and price for each dose of semen : 2.59 and ($6.00) Calculation: Prostaglandin Pre-synchronization cost 0.954 x 2 x ($2.035) = $3.88 Calculation: Prostaglandin Ovsynch/Resynch cost 0.954 x 2.59 x ($2.035) = $5.18 Calculation : GnRH cost 0.954 x 6.01 x ($1.84) = $10.88 Calculation : CIDR cost 0.954 x 2.59 x ($8.43) = $21.48 Calculation : Semen cost 0.954 x 2.59 x ($6.00) = $15.29 2) Labor cost TAI (labor for giving injections, lab or for inserting and removal CIDR) $2.82 3) Breeding expenses (2.59 services per cow per yea r at $ 3.0 each) $7.29 3) Pregnancy check expenses (4.33 times per cow per year at $ 3.0 each) $13.02 Total costs TAI $76.32 Returns 1) Genetic advantage of AI sires Cows calving per year from 2nd or greater lactation : 74.6% Single heifer calves: 48% Heifer calves surviving until freshening: 85% Calves with a genetic advantage: 75.3% x 48% x 85% = 30.4% Average net merit AI sires: $361 / Average net meri t NS sires: $163 (estimated) Time adjusted advantage net merit AI sires: (361-1 63)/3 x (1/1.08)^3 = $52 Calculation: 0.307 x 52 = $15.94 Total returns TAI $15.94 Net costs for TAI = Total returns TAI Total costs TAI Net costs for TAI = $16.09 $78.29 = ($61.84)
117 Table 4-3. Returns and cost ($/slot per year) for the default NS and TAI programs NS TAI Milk sales 4,359.76 4,386.48 Cow sales 102.15 114.33 Calf sales 154.42 148.70 Replacement cost 485.22 543.09 Feed cost 1,199.92 1,203.93 Other costs 730.00 730.00 Reproductive cost 100.53 61.84 Net returns 2,100.66 2,110.66
118 Table 4-4. Simulation of economic balance in dolla rs of TAI over NS considering different scenarios w here arbitrary values for cost of semen are varying accordingly with feed cost, mi lk price and genetic advance using as baseline the cost obtained in this study not accounting the difference in reproductive performance. ITEMS Semen cost $6.00 (Study Price) $2.00 $12.00 $22.00 Results from the study 10.00 48.41 24.11 -0.19 Marginal Feed Cost /cwt $ 2.00 38.69 27.85 3.56 -20.74 $ 5.00 18.13 89.52 65.22 40.93 $ 8.00 79.80 151.19 126.89 102.59 Milk Price ($/cwt) $ 12.00 141.47 48.41 24.11 -0.19 $ 18.00 38.69 48.41 24.11 -0.19 $ 24.00 38.69 48.41 24.11 -0.19 Genetic Advantage of TAI ($)* $ 0.00 38.69 32.47 8.17 -16.12 $ 300.00 22.75 56.62 32.32 8.02 $ 600.00 46.90 119.64 95.35 71.05 *Net merit dollars.
119 Table 4-5. Simulation of economic balance in dollar s of TAI over NS considering different scenarios wh ere arbitrary values for cost o f semen are varying accordingly with feed cost, milk price and genetic advance using as baseline the cos t obtained in this study and accounting for the difference in reproduc tive performance ITEMS Semen cost $ 6.00 (Study Price) $2.00 $12.00 $22.00 Results from the study 10.00 19.72 -4.58 -28.88 Marginal Feed Cost /cwt $2.00 -9.22 0.50 -23.80 -48.10 $5.00 48.44 58.16 33.86 9.57 $8.00 106.10 115.82 91.52 67.23 Milk Price ($/cwt) $12.00 -0.69 9.03 -15.27 -39.56 $18.00 7.33 17.05 -7.25 -31.55 $24.00 15.35 25.06 0.77 -23.53 Genetic Advantage of TAI ($) $0.00 -5.94 3.78 -20.52 -44.81 $300.00 18.21 27.93 3.63 -20.66 $600.00 42.36 52.08 27.78 3.48
120 Table 4-6. Simulation of economic balance in dolla rs of TAI over NS considering different scenarios w here arbitrary different pregnancy rates are varying accordingly with cost o f semen, feed cost, milk price and genetic advance using as baseline the cost obtained in this study not accounting for the difference in reproductive performance. Items PR TAI (%) 24 24 24 18 18 18 12 12 12 PR NS (%) 24 18 12 24 18 12 24 18 12 Results from the study 39.64 57.86 87.00 37.62 55.8 4 84.98 33.46 51.65 80.75 Marginal Feed Cost /cwt $ 2.00 18.61 31.97 53.47 16.59 29.95 51.45 12.43 25 .76 47.21 $ 5.00 81.71 109.65 154.07 79.69 107.63 152.05 75.5 3 103.44 147.81 $ 8.00 144.81 187.33 254.66 142.79 185.31 252.64 13 8.63 181.12 248.41 Milk Price ($/cwt) $ 12.00 39.64 57.86 87.00 37.62 55.84 84.98 33.46 5 1.65 80.75 $ 18.00 39.64 57.86 87.00 37.62 55.84 84.98 33.46 5 1.65 80.75 $ 24.00 39.64 57.86 87.00 37.62 55.84 84.98 33.46 5 1.65 80.75 Genetic Advantage of TAI ($) $ 0.00 23.85 42.07 71.21 22.97 41.19 70.34 20.72 38 .90 68.00 $ 300.00 47.77 66.00 95.14 45.17 63.39 92.53 40.03 58.22 87.31 $ 600.00 71.70 89.92 119.06 67.36 85.58 114.72 59.3 5 77.54 106.63 Semen Cost/dose $ 2.00 49.45 68.08 97.80 47.42 66.06 95.78 43.40 62 .01 91.68 $ 12.00 24.93 42.53 70.81 22.91 40.52 68.80 18.56 3 6.12 64.34 $ 22.00 0.41 16.98 43.82 -1.60 14.97 41.82 -6.28 10 .24 37.00
121 Table 4-7. Simulation of economic balance in dolla rs of TAI over NS considering different scenarios w here arbitrary different pregnancy rates are varying accordingly with cost o f semen, feed cost, milk price and genetic advance using as baseline the cost obtained in this study accounting for the difference in reproductive performance. Items PR TAI (%) 24 24 24 18 18 18 12 12 12 PR NS (%) 24 18 12 24 18 12 24 18 12 Results from the study 36.17 108.34 226.44 -19.71 52.46 170.56 -114.19 -42.06 75.99 Marginal Feed Cost /cwt $ 2.00 17.01 82.95 189.27 -37.11 28.83 135.15 -127.40 -61.50 44.78 $ 5.00 74.51 159.13 300.79 15.11 99.73 241.39 -87.77 -3.18 138.43 $ 8.00 132.01 235.32 412.31 67.33 170.64 347.62 -48.14 55.14 232.08 Milk Price ($/cwt) $ 12.00 21.16 104.25 255.48 -48.79 34.29 185.53 -176.86 -93.82 57.37 $ 18.00 32.42 107.32 233.70 -26.98 47.92 174.30 -129.86 -55.00 71.34 $ 24.00 43.68 110.39 211.92 -5.17 61.55 163.0 8 -82.86 -16.18 85.30 Genetic Advantage of TAI ($) $ 0.00 20.38 92.55 210.65 -34.35 37.82 155.91 -126.94 -54.81 63.24 $ 300.00 44.31 116.48 234.58 -12.16 60.01 178.1 1 -107.63 -35.49 82.56 $ 600.00 68.23 140.40 258.50 10.03 82.20 200.3 0 -88.31 -16.17 101.88 Semen Cost/dose $ 2.00 45.98 118.56 237.24 -9.90 62.68 181.35 -104.26 -31.70 86.93 $ 12.00 21.46 93.01 210.25 -34.41 37.14 154.3 7 -129.10 -57.59 59.59 $ 22.00 -3.05 67.46 183.26 -58.92 11.60 127. 39 -153.93 -83.47 32.25
122 Table 4-8. Simulation of economic balance in dolla rs of TAI over NS considering different scenarios w here arbitrary different pregnancy rates and opportunity cost generated by r eplacement of bull for lactating cows accordingly w ith the number of slot available in one population of 100 animals. TAI Pregnancy Rates NS Pregnancy Rates slots 1000 1000 1000 cows 1000 986 972 bulls 0 14 28 Results from the study Results from the study 10.00 39.41 68.82 24% 24% 36.17 65.11 94.04 24% 18% 108.34 136.23 164.12 24% 12% 226.44 252.62 278.81 18% 24% -19.71 9.23 38.16 18% 18% 52.46 80.35 108.24 18% 12% 170.56 196.75 222.93 12% 24% -114.19 -85.26 -56.33 12% 18% -42.06 -14.17 13.72 12% 12% 75.99 102.18 128.36
CHAPTER 5 GENERAL DISCUSSION AND CONCLUSIONS Inefficient estrus detection is a major factor for the low reproductive performance observed in dairy farms throughout the U.S.A.. Consequently, research in dairy cattle reproductive management has focused intensely in methods to mini mize the negative impact that inefficient estrus detection has on fertility. Arguably, NS or TAI are two breeding systems that can be used by dairy producers to mitigate the challenges of es trus detection. This is the first study that evaluated reproductive performance and economics of TAI and NS to reproductively managed dairy cows. Timed AI and NS were compared under a f ield trial where all possible variables were accounted and all conditions considered in ord er to optimize reproductive performance and to increase the likelihood of reasonable results wi th minimal possible confounding effects. Both of the breeding program resulted in an excell ent reproductive performance. The TAI breeding program did not result in a greater 21-d c ycle pregnancy rate compared with NS as initially hypothesized. A greater proportion of pre gnant cows at the end of the study occurred in NS bred cows because they had more breeding opportu nities than TAI. The interval between breeding opportunities was 35 days for cows enrolle d in the TAI program. On the other hand, if you consider length of an estrous cycle to be aroun d 21 days, it is likely that cows bred by NS had a breeding opportunity every 21 days. When rep roductive performance was compared to the same breeding eligibility period of 21-d cycle preg nancy rate, there was no difference between NS and TAI. Therefore, the greater proportion of pr egnant cows at the end of the study and the greater daily hazards of pregnancy for NS can be at tributed to the greater opportunity that NS cows had. Furthermore, a herd budget calculator was created, which allowed evaluation of costs and revenues of both breeding program accounting fo r the difference in 21-d cycle pregnancy rates. The economic analysis of this study revealed that the TAI breeding program was $38.69
less expensive than NS breeding program, contradict ing the belief that the use of bulls is the cheapest method to breed dairy cows avoiding proble ms with estrous detection. The main variables for this difference were feeding cost for bulls and genetic advantage of TAI sires. The differences in profit were even greater when opport unity cost that result by the replacement of bulls by lactating cows was taken in consideration. Therefore, TAI is the most economical breeding program option to eliminate problems with estrus detection in lactating dairy. In conclusion, NS and TAI are two breeding systems that can be used strategically to minimize problems related with detection of estrus, but the extended inter-insemination interval in TAI reduces daily pregnancy rate because these c ow have fewer opportunities for breeding. However, the high price of feeding bulls and greate r genetic advantage obtained with TAI makes this breeding program the most economical method to eliminate estrus detection problems in lactating dairy cows.
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BIOGRAPHICAL SKETCH Fbio Soares de Lima was born on January 30, to Gas par de Lima and Dolores Soares de Lima in Muzambinho, Minas Gerais, Brazil. He is the third of four children that grew up in a dairy farm and was surrounded by cows from an early age. After graduation from high school he was accepted and enrolled in the college of veterin ary medicine at So Paulo State University, where he had an opportunity to work under the super vision of Dr Jos Lus Moraes Vasconcelos. In 2004, during the clinical year of his veterinary studies he spent 5 months at the University of Wisconsin, in Madison working with physiology of re production, health and reproductive management of dairy cows under the supervision of D r Milo Wiltbank. After his graduation from So Paulo State University, he worked for 18 months at the University of California, Davis in the Veterinary Medicine Teaching and Research Center in Tulare, under the supervision of Dr Jos Eduardo P. Santos, conducting research in the areas of dairy cow nutrition, reproduction and health. In July 2006, he was accepted as resident i n the Food Animal Reproduction and Medicine Program at University of Florida College of Veterin ary Medicine. In 2007, he started a master degree program under the supervision of Dr Carlos R isco. After completion of his MS degree he will remain at University of Florida to pursue PhD degree.