Presynchronization of suckled beef cows with human chorionic gonadotropin (hCG) 7 days prior to initiation of a fixed-ti...

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Presynchronization of suckled beef cows with human chorionic gonadotropin (hCG) 7 days prior to initiation of a fixed-time artificial insemination protocol fails to enhance fertility
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2009 Florida Beef Report
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Marquezini, Guilherme
Dahlen, Carl
Lamb, G. Cliff
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Institute of Food and Agricultural Sciences, University of Florida
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Gainesville, Fla.
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Presynchronization of Suckled Beef Cows with Human Chorionic
Gonadotropin (hCG) 7 days prior to Initiation of a Fixed-time Artificial
Insemination Protocol Fails to Enhance Fertility


Guilherme Marquezini1
Carl Dahlent
G. Cliff Lamb1


Administration of human chorionic gonadotropin 7 d before initiating the CO-Synch + CIDR estrous
synchronization protocol failed to enhance pregnancy rates. When replacing gonadotropin releasing
hormone with human chorionic gonadotropin at the time of insemination, pregnancy rates to fixed-time
artificial insemination may be reduced.


Summary
Two experiments were conducted to evaluate
whether hCG administered 7 d before initiating
the CO-Synch + CIDR estrous synchronization
protocol (Exp. 1 and 2), or replacing
gonadotropin releasing hormone (GnRH) with
human chorionic gonadotropin (hCG) at the
time of insemination (Exp. 1), would alter
pregnancy rate to a fixed-time artificial
insemination (TAI) in suckled beef cows. In
Exp. 1, cows were stratified by days postpartum,
age, and parity and randomly assigned to one of
four treatments: 1) Cows received GnRH at
CIDR insertion (d -7) and 25 mg of
prostaglandin F2[ (PG) at CIDR removal (d 0),
followed in 64 to 68 hr by a TAI with second
injection of GnRH at the time of insemination
(CG; n=29); 2) same as CG but the second
injection of GnRH at the time of insemination
was replaced by hCG (CH; n=28); 3) same as
GG, but cows received hCG7 d (d -14) priorto
CIDR insertion (HG; n=29); and 4) sameas GH,
but cows received hCG 7 d (d -14) priorto CIDR
insertion (HH; n=29). Pregnancy rates were
52%, 41%, 59%, and 38%for GG, GH, HG, and
HH, respectively. Cows receiving hCG(39%) in
place of GnRH at TAI tended (P 0.06) to have
poorer pregnancy rates than those receiving
GnRH (56%). In Exp. 2, cows were stratified
based on days postpartum, body condition score
(BCS), breed type, and calf sex and then
assigned to the CG (n 102) or HG (n


S103) treatments. Overall pregnancy rates
were 51%, but no differences in pregnancy rates
were detected between treatments, breed, days
postpartum, or calf sex. We concluded that
presynchronization with hCG 7d prior to
initiation of the CO-Synch + CIDR protocol
failed to enhance pregnancy rates, but replacing
GnRH with hCG at the time ofAI may reduce
pregnancy rates.

Introduction
Producers are continually seeking to improve
reproductive efficiency in cattle. One method of
enhancing reproductive efficiency is to utilize
estrous synchronization (ES) and AI. Effective
TAI systems have been developed (Larson et al.,
2006) that reduce the amount of time and labor
associated with estrous synchronization and
TAI. To ensure the greatest response to ES and
AI, increasing the percentage of cows cycling at
the beginning of the breeding season is
paramount. Therefore, the use of
presynchronization to initiate estrous cycles in
noncycling cows may enhance the response to
the ES and AI protocol. Presynchronization
protocols have been developed to increase the
rate of ovulation by the first administration of
GnRH in a GnRH-PG-GnRH protocol (Busch et
al., 2007). Presynchronization of estrus with 2
injections of PG administered 14 d apart, prior to
initiating a TAI protocol enhanced pregnancy


2009 Florida BeefReport










rates in cows (Moreira et al., 2001; Navanukraw
et al., 2004). The improvement of the response
of the GnRH is believed to be causedby an
increased proportion of cows in early to mid-
diestrus when the first GnRH injection of the
timed AI protocol was administered,
(Vasconcelos et al., 1999; Moreira et al., 2000).
The use of hCG induces potent LH activity on
ovarian cells, which can even lead to ovulation
throughout the estrous cycle.

Our objectives were: 1) to evaluate whether hCG
administered 7 d before initiating a TAI estrous
synchronization protocol would enhance
pregnancy rates; and 2) whether replacing
GnRH with hCG at the time of insemination
would alter pregnancy rate to TAI.

Materials and Methods
Experiment 1.
One hundred fifteen cows were stratified by
days postpartum, age, and parity before being
assigned to one of four treatments in a 2 x 2
factorial arrangement (Figure 1): 1) cows
received a 100 ig injection of GnRH (OvaCyst;
IVX Animal Health) and a CIDR containing
1.38 g of progesterone (Pfizer Animal Health)
on d -7 and 25 mg of PG (Lutalyse, dinoprost
tromethamine, Pfizer Animal Health) at CIDR
removal (d 0), followed in 67 hr by a TAI with
second injection of GnRH at the time of
insemination (Control GnRH; CG; n=29); 2)
same as CG but a second injection of GnRH at
the time of insemination was replaced by 1,000
IU of hCG (CH; n=28); 3) same as CG, but
cows received 1,000 IU ofhCG administered 7 d
(d-14) before CIDR insertion (HG; n=29); and
4) same as CH, but cows received 1,000 IU of
hCG on d -14 (HH; n=29). Blood samples were
collected on d -24, -14,-7, 0, 3, 10 and 16 to
harvest serum for analysis of concentration of
progesterone. Progesterone concentration was
used to determine cycling status. Pregnancy was
diagnosed by transrectal ultrasonography 31 d
after TAI.

Experiment 2.
Two hundred and five cows were stratified
based on days postpartum, BCS, breed type
(British or Crossbreed), and calf sex (male or
female) and assigned to CG (n= 102) and HG (n


= 103) treatments from Experiment 1 (Figure 1).
Mean BCS was 5.5 and days postpartum was 70
d. Pregnancy was diagnosed by transrectal
ultrasonography on d 29 after TAI.

Results
Experiment 1.
Incidence of cycling, concentrations of
progesterone, and pregnancy rates did not differ
among the four treatments, but when evaluated
as a 2 x 2 factorial differences were detected.
Cows receiving no pretreatment (control) or
hCG on d -14 are illustrated in Table 1, whereas
comparisons between cows treated with GnRH
or hCG at TAI (d 3) are illustrated in Table 2.
Overall, 55% of cows were cycling by d -14 and
did not differ between treatments; however, the
percentage of cycling cows tended (P = 0.10) to
increase by d -7 after receiving hCG (78.9%)
compared to untreated controls (64.9%).
Subsequently, the concentrations of
progesterone (P4) tended (P = 0.13) to be
greater at the time of CIDR insertion (d -7) in
cows receiving hCG compared to untreated
controls. The enhanced incidence of more cows
with a corpus luteum on d -7 did not appear to
enhance fertility. Overall pregnancy rates were
47.4% and were not altered by pretreatment with
hCG. However, pregnancy rates tended (P =
0.06) to be reduced in cows receiving hCG at
TAI compared to those receiving GnRH.

We conclude that hCG appeared to influence the
percentage of cows with a corpus luteum on d -7
but failed to enhance fertility when administered
7 d prior to initiation of ES. In addition,
replacing GnRH with hCG at TAI appeared to
suppress pregnancy rates.

Experiment 2.
Overall pregnancy rates were 51% and did not
differ among treatments. In addition, breed, sex
of offspring, days postpartum, and parity did not
appear to influence pregnancy rates (Table 3).
Therefore, we conclude that presynchronization
with hCG 7 d prior to initiating the CO-Synch +
CIDR protocol, did not enhance pregnancy rates.


2009 Florida BeefReport





























Acknowledgements
We thank Pfizer Animal Health (New York, NY) for contributions of prostaglandin F2a(Lutalyse) and
CIDR inserts and IVX Animal Health (St. Joseph, MO) for donation of gonadotropin-releasing hormone
(OvaCyst). Appreciation also is expressed to S. Bird, R. Irurtia, A. Martins, Jr., Olivia Helms, Don
Jones, Mary Maddox, Todd Matthews, Harvey Standland, and David Thomas for their assistance with
data collection and laboratory analysis.








LITERATURE CITED
Busch et al. 2007. J. Anim. Sci. 85: 1933.
Larson et al. 2006. J. Anim. Sci. 84:332.
Moreira et al. 2001. J. Dairy Sci. 84:1646.
Moreira et al. 2000. J. Anim. Sci. 78:1568.
Navanukraw et al. 2004. J. Dairy Sci. 87:1551.
Vasconcelos et al. 1999. Theriogenology 52:1067.







'Guilherme Marquezini, Graduate Student, UF/IFAS, NFREC, Marianna, FL; Carl Dahlen, Graduate
Student, University of Minnesota, NWROC, Crookston, MN; G. Cliff Lamb, Associate Professor,
UF/IFAS, NFREC, Marianna, FL


2009 Florida BeefReport

























GnRH PGF

CIDR
Ak io


GnRH PGF

CIDR
I cion,


GnRH PGF

CIDR


hCG





-25 -14


GnRH PGF

CIDR


0


Figure 1. Schematic of experimental design for cows treated with PG, CIDR, and GnRH or hCG in
Exp. 1 (CG, CH, HG, and HH) and Exp. 2 (CG and HG).


2009 Florida BeefReport


CG


CH


0


HG


0


TAI and
GnRH





3

TAI and
hCG





3
TAI and
GnRH





3

TAI and
hCG





3


HH


0


W 9


i













Table 1. Concentrations of progesterone (P4), percentage of cycling, and pregnancy rates in
cows receiving either control or hCG treatment on d -14 (Exp. 1).

Treatment on d -14a


Item Control (CG and CH) hCG (HG and HH)

----------ng/ml----------


P4 on d -14, ng/ml 1.6 0.2 1.5 0.2

P4 on d -7, ng/ml 1.9 0.4 2.7 0.4

P4 on d 0, ng/ml 2.5 0.3 3.1 0.3

----------no./no. (%)----------

Cycling cows on d -14b 31/57 (54.4) 32/57 (56.1)

Cycling cows on d -7 37/57 (64.9)" 45/57 (78.9)"

Cows with >1 ng/ml P4 on d -14d 26/57 (45.6) 27/57 (47.4)

Cows with >1 ng/ml P4 on d -7d 23/57 (40.4)Y 36/57 (63.2)z

Pregnancy rates 26/57 (45.6) 28/57 (49.1)

aCows were assigned to receive no treatment or hCG on d -14.
bNumber and percentage of cows cycling on d -14 based on two blood samples taken on d d -25
and -14.
CNumber and percentage of cows cycling on d -7 based on three blood samples taken on d d -25, -
14, and -7.
dCows with concentrations of P4 >1 ng/ml on d-14 or -7.
"xPercentages differ (P = 0.10).
Y'Percentages differ (P < 0.05).


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Table 2. Concentrations of progesterone (P4) and pregnancy rates in cows receiving either
GnRH or hCGat TAI on d 3 (Exp. 1).

Treatment on d 3a


Item GnRH (CG and HG) hCG (CH and HH)

----------ng/ml----------

P4 on d 3, ng/ml 0.1 0.2 0.2 0.2

P4 on d 10, ng/ml 2.4 0.2 2.3 0.2

P4 on d 16, ng/ml 3.4 0.3 3.4 0.3

P4 on d 29, ng/ml 2.8 0.4 2.6 0.4

----------no./no. (%)----------

Pregnancy rates 32/57 (56.1)x 22/57 (38.6)Y

aCows were assigned to receive GnRH or hCG on d 3 (at the time of TAI).
x"yPercentages differ (P = 0.06).


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Table 3. Pregnancy rates of cows assigned to receive control or hCG treatment on d -14 (Exp.2).


Treatments


Item CG HG

----------no./no. (%)----------

Breed

Bos taurus 16/37 (43.2) 24/45 (53.3)

Bos indicus crossbred 35/63 (55.6) 26/55 (47.3)

Calf sex

Female 22/43 (51.1) 22/42 (52.4)

Male 28/55 (50.9) 24/53 (45.3)

Days postpartum

<60 d 12/25 (48.0) 11/27 (40.7)

>60 d 40/76 (52.6) 39/74 (52.7)

Parity

Primiparous 10/20 (50.0) 9/25 (36.0)

Multiparous 42/81 (51.9) 41/76 (53.9)

aCows were assigned to receive no treatment or hCG on d -14.


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Full Text

PAGE 1

Presynchronization of Suckled Beef Cows with Human Chorionic Gonadotropin (hCG) 7 days p rior to Initiation of a Fixed time Artificial Insemination Protocol Fails to Enhance Fertility Guilherme Marquezini 1 Carl Dahlen 1 G. Cliff Lamb 1 Summary Two experiments were conducted to evaluate whether hCG administered 7 d before initiating the CO-Synch + CIDR estrous synchronization protocol (Exp. 1 and 2), or replacing gonadotropin releasing hormone ( GnRH ) with human chorionic gonadotropin (hCG ) at the time of insemination (Exp. 1), would alter pregnancy rate to a fixed-time artificial insemination ( TAI ) in suckled beef cows. In Exp. 1, cows were stratified by days postpartum, age, and parity and randomly assigned to one of four treatments: 1) Cows received GnRH at CIDR insertion (d -7) and 25 mg of prostaglandin F 2 (PG) at CIDR removal (d 0), followed in 64 to 68 hr by a TAI with second injection of GnRH at the time of insemination (CG; n=29); 2) same as CG but the second injection of GnRH at the time of insemination was replaced by hCG (CH; n=28); 3) same as GG, but cows received hCG7 d (d -14) priorto CIDR insertion (HG; n=29); and 4) sameas GH, but cows received hCG 7 d (d -14) priorto CIDR insertion (HH; n=29). Pregnancy rates were 52%, 41%, 59%, and 38% for GG, GH, HG, and HH, respectively. Cows receiving hCG(39%) in place of GnRH at TAI tended (P = 0.06) to have poorer pregnancy rates than those receiving GnRH (56%). In Exp. 2, cows were stratified based on days postpartum, body condition score (BCS), breed type, and calf sex and then assigned to the CG (n = 102) or HG (n = 103) treatments. Overall pregnancy rates were 51%, but no differences in pregnancy rates were detected between treatments, breed, days postpartum, or calf sex. We concluded that presynchronization with hCG 7d prior to initiation of the CO-Synch + CIDR protocol failed to enhance pregnancy rates, but replacing GnRH with hCG at the time of AI may reduce pregnancy rates. Introduction Producers are continually seeking to improve reproductive efficiency in cattle. One method of enhancing reproductive efficiency is to utilize estrous synchronization (ES) and AI. Effective TAI systems have been developed (Larson et al., 2006) that reduce the amount of time and labor associated with estrous synchronization and TAI. To ensure the greatest response to ES and AI, increasing the percentage of cows cycling at the beginning of the breeding season is paramount. Therefore, the use of presynchronization to initiate estrous cycles in noncycling cows may enhance the response to the ES and AI protocol. Presynchronization protocols have been developed to increase the rate of ovulation by the first administration of GnRH in a GnRHPG -GnRH protocol (Busch et al., 2007). Presynchronization of estrus with 2 injections of PG administered 14 d apart, prior to initiating a TAI protocol enhanced pregnancy Administration of human chorionic gonadotropin 7 d before initiating the CO Synch + CIDR estrous synchronization protocol failed to enhance pregnancy rates. When replacing gonadotropin releasing hormone with human chorionic gonadotropin at the time of ins emination, pregnancy rates to fixed time artificial insemination may be reduced.

PAGE 2

rates in cows ( Moreira et al., 2001 ; Navanukraw et al., 2004 ). The improvement of the response of the GnRH is believed to be causedby an increased proportion of cows in early to middiestrus when the first GnRH injection of the timed AI protocol was administered, ( Vasconcelos et al., 1999 ; Moreira et al., 2000 ). The use of hCG induces potent LH activity on ovarian cells, which can even lead to ovulation throughout the estrous cycle. Our objectives were: 1) to evaluate whether hCG administered 7 d before initiating a TAI estrous synchronization protocol would enhance pregnancy rates; and 2) whether replacing GnRH with hCG at the time of insemination would alter pregnancy rate to TAI. Materials and Methods Experiment 1. One hundred fifteen cows were stratified by days postpartum, age, and parity before being assigned to one of four treatments in a 2 x 2 factorial arrangement (Figure 1): 1) cows received a 100 g injection of GnRH (OvaCyst; IVX Animal Health) and a CIDR containing 1.38 g of progesterone (Pfizer Animal Health) on d -7 and 25 mg of PG (Lutalyse, dinoprost tromethamine, Pfizer Animal Health) at CIDR removal (d 0), followed in 67 hr by a TAI with second injection of GnRH at the time of insemination (Control GnRH; CG; n=29); 2) same as CG but a second injection of GnRH at the time of insemination was replaced by 1,000 IU of hCG (CH; n=28); 3) same as CG, but cows received 1,000 IU of hCG administered 7 d (d -14) before CIDR insertion (HG; n=29); and 4) same as CH, but cows received 1,000 IU of hCG on d -14 (HH; n=29). Blood samples were collected on d -24, -14,-7, 0, 3, 10 and 16 to harvest serum for analysis of concentration of progesterone. Progesterone concentration was used to determine cycling status. Pregnancy was diagnosed by transrectal ultrasonography 31 d after TAI. Experiment 2. Two hundred and five cows were stratified based on days postpartum, BCS, breed type (British or Crossbreed), and calf sex (male or female) and assigned to CG (n= 102) and HG (n = 103) treatments from Experiment 1 (Figure 1). Mean BCS was 5.5 and days postpartum was 70 d. Pregnancy was diagnosed by transrectal ultrasonography on d 29 after TAI. Results Experiment 1. Incidence of cycling, concentrations of progesterone, and pregnancy rates did not differ among the four treatments, but when evaluated as a 2 x 2 factorial differences were detected. Cows receiving no pretreatment (control) or hCG on d -14 are illustrated in Table 1, whereas comparisons between cows treated with GnRH or hCG at TAI (d 3) are illustrated in Table 2. Overall, 55% of cows were cycling by d -14 and did not differ between treatments; however, the percentage of cycling cows tended ( P = 0.10) to increase by d -7 after receiving hCG (78.9%) compared to untreated controls (64.9%). Subsequently, the concentrations of progesterone (P4) tended ( P = 0.13) to be greater at the time of CIDR insertion (d -7) in cows receiving hCG compared to untreated controls. The enhanced incidence of more cows with a corpus luteum on d -7 did not appear to enhance fertility. Overall pregnancy rates were 47.4% and were not altered by pretreatment with hCG. However, pregnancy rates tended ( P = 0.06) to be reduced in cows receiving hCG at TAI compared to those receiving GnRH. We conclude that hCG appeared to influence the percentage of cows with a corpus luteum on d -7 but failed to enhance fertility when administered 7 d prior to initiation of ES. In addition, replacing GnRH with hCG at TAI appeared to suppress pregnancy rates. Experiment 2. Overall pregnancy rates were 51% and did not differ among treatments. In addition, breed, sex of offspring, days postpartum, and parity did not appear to influence pregnancy rates (Table 3). Therefore, we conclude that presynchronization with hCG 7 d prior to initiating the CO-Synch + CIDR protocol, did not enhance pregnancy rates.

PAGE 3

Acknowledgements We thank Pfizer Animal Health (New York, NY) for contributions of prostaglandin F 2 (Lutalyse) and CIDR inserts and IVX Animal Health (St. Joseph, MO) for donation of gonadotropin releasing hormone (OvaCyst). Appreciation also is expressed to S. Bird, R. Irurtia, A. Martins, Jr., Olivia Helms, Don Jones, Mary Maddox, Todd Matthews, Harve y Standland, and David Thomas for their assistance with data collection and laboratory analysis. LITERATURE CITED Busch et al. 2007. J. Anim. Sci. 85: 1933 Larson et al. 2006. J. Anim Sci. 84:332 Moreira et al. 2001. J. Dairy Sci. 84:1646 Moreira et al. 2000. J. Anim. Sci. 78:1568 Navanukraw et al. 2004. J. Dairy Sci. 87:1551 Vasconcelos et al 1999. Theriogenology 52:1067 1 Guilherme Marquezini, Graduate Student, UF/IFAS, NFREC, Marianna, FL; Carl Dahlen, Graduate Student, University of Minnesota, NWROC, Crookston, MN; G. Cl iff Lamb, Associate Professor, UF/IFAS, NFREC, Marianna, FL

PAGE 4

Figure 1. Schematic of experimental design for cows treated with PG, CIDR, and GnRH or hCG in Exp. 1 (CG, CH, HG, and HH) and Exp. 2 (CG and HG).

PAGE 5

Table 1. Concentrations of progesterone (P4), percentage of cycling, and pregnancy rates in cows receiving either control or hCG treatment on d 14 (Exp. 1). Treatment on d 14 a Item Control (CG and CH) hCG (HG and HH) ---------ng/ml ---------P4 on d 14, ng/ml 1.6 0.2 1.5 0.2 P4 on d 7, ng/ml 1.9 0.4 2.7 0.4 P4 on d 0, ng/ml 2.5 0.3 3.1 0.3 ---------no./no. (%) ---------Cycling cows on d 14 b 31/57 (54.4) 32/57 (56.1) Cycling cows on d 7 c 37/57 (64.9) w 45/57 (78.9) x Cows with >1 ng/ml P4 on d 14 d 26/57 (45.6) 27/57 (47.4) Cows with >1 ng/ml P4 on d 7 d 23/57 (40.4) y 36/57 (63.2) z Pregnancy rates 26/57 (45.6) 28/57 (49.1) a Cows were assigned to receive no treatment or hCG on d 14. b Number and percentage of cows cycling on d 14 based on two blood samples taken on d d 25 and 14. c Number and percentage of cows cycling on d 7 based on three blood samples taken on d d 25, 14, and 7. d Cows with concentrations of P4 >1 ng/ml on d 14 or 7. w,x Percentages differ (P = 0.10). y,z Percentages differ (P < 0.05).

PAGE 6

Table 2. Concentrations of progesterone (P4) and pregnancy rates in cows receiving either GnRH or hCGat TAI on d 3 (Exp. 1). Treatment on d 3 a Item GnRH (CG and HG) hCG (CH and HH) ---------ng/ml ---------P4 on d 3, ng/ml 0.1 0.2 0.2 0.2 P4 on d 10, ng/ml 2.4 0.2 2.3 0.2 P4 on d 16, ng/ml 3.4 0.3 3.4 0.3 P4 on d 29, ng/ml 2.8 0.4 2.6 0.4 ---------no./no. (%) ---------Pregnancy rates 32/57 (56.1) x 22/57 (38.6) y a Cows were assigned to receive GnRH or hCG on d 3 (at the time of TAI). x y P ercentages differ (P = 0.06).

PAGE 7

Table 3. Pregnancy rates of cows assigned to receive control or hCG treatment on d 14 (Exp.2). Treatments a Item CG HG ---------no./no. (%) ---------Breed Bos t aurus 16/37 (43.2) 24/45 (53.3) Bos i ndicus crossbred 35/63 (55.6) 26/55 (47.3) Calf sex Female 22/43 (51.1) 22/42 (52.4) Male 28/55 (50.9) 24/53 (45.3) Days postpartum <60 d 12/25 (48.0) 11/27 (40.7) >60 d 40/76 (52.6) 39/74 (52.7) Parity Primiparous 10/20 (50.0) 9/25 (36.0) Multiparous 42/81 (51.9) 41/76 (53.9) a Cows were assigned to receive no treatment or hCG on d 14.