Fixed-time artificial insemination (TAI) in suckled beef cows in response to equine chorionic gonadotropin (eCG)

MISSING IMAGE

Material Information

Title:
Fixed-time artificial insemination (TAI) in suckled beef cows in response to equine chorionic gonadotropin (eCG)
Physical Description:
Book
Creator:
Marquezini, Guilherme
Mercadante, Vitor
Wallace, Logan
Pulley, Stacey
Olson, KC
Jaeger, Jon
Bischoff, Kalyn
Loyd, Tera
Stevenson, Jeff
Lamb, G. Cliff
Publisher:
Institute of Food and Agricultural Sciences, University of Florida
Place of Publication:
Gainesville, Fla.
Publication Date:

Record Information

Source Institution:
University of Florida Institutional Repository
Holding Location:
University of Florida
Rights Management:
All rights reserved by the source institution and holding location.
System ID:
AA00000425:00001


This item is only available as the following downloads:


Full Text







Fixed-Time Artificial Insemination (TAI) in Suckled Beef Cows in Response
to Equine Chorionic Gonadotropin (eCG)


Guilherme Marquezini1, Vitor Mercadante1, Logan Wallace2, Stacey Pulley2, KC Olson2, Jon
Jaeger2, Kalyn Bischoff1, Tera Loyd1, Jeff Stevenson2, G. Cliff Lamb1



Administration of equine chorionic gonadotropin (eCG) at the time of prostaglandin (PGF) and CIDR
removal of the CO-synch + CIDR protocol does not enhance pregnancy rates. Administration of eCG
tended to increase follicle diameter at the time of insemination and increased progesterone
concentration and corpus luteum volume seven days after AI.


Summary
Two experiments were conducted to evaluate
whether eCG at the time of PGF injection had
an effect on estradiol concentration in blood,
dominant follicle diameter at timed artificial
insemination (TAI), concentrations of
progesterone (P4) and corpus luteum (CL)
volume 7 d after TAI, and improves pregnancy
rates. In Experiment 1, suckled beef cows (n =
513; pure- and crossbred Angus, Simmental,
and Hereford) were enrolled in a 7-d CO-Synch
+ CIDR protocol (100 /ig gonadotropin
releasing hormone [GnRH] at controlled
internal drug release device [CIDR] insertion [d
-7]; 25 mg prostaglandin F2a [PGF] at CIDR
removal [d 0]; and 100 /ig GnRH at TAI 66 h
after PGF [d 3]) at three locations. Cows were
randomly assigned to be controls or receive
eCG (400 IU) at the time of PGF injection and
CIDR insert removal. Pregnancy was diagnosed
by transrectal ultrasonography at median d 35
and 67 after TAI. Serum P4 concentration was
determined in blood samples collected on d -17,
-7, 0, 3, and at both pregnancy diagnoses
(pregnant cows only) to determine cycling
status, luteolysis, and potential differences in CL
function after TAI. Unadjusted pregnancy rates
(PR) on d 35 was 42.9 vs. 49.8% for eCG vs.
controls, respectively. Cycling cows were 1.5
times more (P = 0.05) likely to conceive than
noncycling cows. Control cows were 1.5 times
more (P 0.04) likely to conceive than those


treated with eCG. In Experiment 2, 35 cows
were stratified by days postpartum and body
condition score (BCS) and assigned to one of
four treatments. Treatment 1 (control, CO; n =
9) and 2 (eCG; n = 9) were the same as
described in Experiment 1; treatment 3 (COCR;
n = 9) was the same as CO but calves were
temporarily removed for 72 h between PGF and
TAI; treatment 4 (eCGCR; n = 8) was the same
as treatment 3 plus an additional injection of
eCG (400 IU) was given at the time of CIDR
removal. Ultrusonographiy was performed on d
0, 3, and 10 to evaluate follicle development and
ovulation, CL regression between d 0 and 3 and
CL volume on d 10. Blood samples were
collected on d 0, 3, and 10 to measure P4
concentrations. Blood samples were collected
every 12 h between d 0 and 3 to measure
estradiol concentration in blood. Progesterone
concentration on d 10 was greater (P < 0.01)
for all the treatments compared with CO (1.4 vs
2.7 vs 2.7 and 2.8 ng/ml for CO, COCR, eCG,
and eCGCR respectively). Follicle diameter
tended (P = 0.09) to be greater for eCG than
CO 48 h after eCG injection while COCR and
eCGCR were intermediate (12.9, 13.1, 15.3, and
14.4 mm, for CO, COCR, eCG and eCGCR,
respectively). Corpus luteum volume was
greater (P < 0.05) on d 10 for eCGCR
compared with CO and COCR (3.8 vs 2.1 vs 1.6
cm3, for eCGCR, CO and COCR, respectively)


'North Florida Research and Education Center, University of Florida, Marianna, FL
2Department of Animal Sciences and Industry, Kansas State University, Manhattan, KS









while eCG was intermediate (2.9 0.5 cm3) but
also greater (P < 0.05) than COCR. Estradiol
concentration was greater (P < 0.05) for eCG
treatment compared with control and eCGCR at
24 h (1.5 vs 0.5 vs 0.9 pg/ml, respectively) and
36 h (1.5 vs 0.4 vs 0.6 pg/ml, respectively) while
COCR was intermediate (1.1 and 1.0 pg/ml, at
24 and 36 h, respectively). We conclude that
eCG tended to increase dominant follicle
diameter at TAI and increase concentrations of
P4 and CL volume 7 d after TAI, however it did
not improve pregnancy rates.

Introduction
Evidence exists that eCG and estradiol
administration are important for a desirable
pregnancy outcome in protocols for anestrous
cows. Because no legal estrogen product is
available in the U.S. market for use in cattle, we
believed we could duplicate the estrogen effect
by administering an appropriately small dose of
eCG during the latter part of follicular
maturation to stimulate more estradiol
biosynthesis without inducing follicular
proliferation (super-ovulation). We hypothesized
that administering a small dose of eCG would
stimulate greater estradiol secretion associated
with follicular maturation that would mimic the
pro-fertility effects of estradiol administration in
beef cows. Support for this hypothesis is
founded in studies where 400 IU of eCG were
administered to cattle at the time of progesterone
insert removal and ovulation was induced by
estradiol benzoate before timed AI (Baruselli et
al., 2003). Pregnancies per AI were increased in
response to eCG (38.9 vs. 54.7%). Their
hypothesis was that increased fertility resulted
from stimulated luteal function in the CL that
resulted from ovulation of follicles exposed to
eCG. Using a similar protocol, it was reported
that despite a similar-sized preovulatory follicle,
both the CL size and concentrations of
progesterone in blood plasma post-estrus were
increased after eCG (Bergamaschi et al., 2005).
The effects on eCG on circulating
concentrations of estradiol were not quantified,
but were likely increased in response to eCG-
stimulated estradiol biosynthesis by the
dominant follicle. Therefore, potentially
increasing concentrations of estradiol by eCG
administration after dominant follicle selection


and near the time of induced luteolysis may
duplicate the profertility effects in lactating
cows that have been demonstrated by
administering estrogen 24 to 36 h after induced
luteolysis. The objective of Experiment 1 was to
evaluate if eCG administered at time of PGF and
CIDR insert removal will improve pregnancy
rates in suckled beef cows. The objective of
Experiment 2 was to evaluate if eCG would alter
follicle diameter at the time of insemination and
increases concentrations of P4 and CL volume
seven days after timed AI.

Materials and Methods
Experiment 1
Suckled beef cows (n = 513; pure- and crossbred
Angus, Simmental, and Hereford) were enrolled
in a 7-d CO-Synch + CIDR protocol (100 gg
GnRH at CIDR insertion [d -7]; 25 mg PGF2,
(PGF) at CIDR removal [d 0]; and 100 gg
GnRH at AI 66 h after PGF [d 3]) at three
locations. Cows were randomly assigned to be
Controls or receive eCG (400 IU im) at the time
of PGF injection and CIDR insert removal
(Figure 1). Pregnancy was diagnosed by
transrectal ultrasonography at median d 35 and
67 after AI. Serum P4 concentration (ng/mL)
was determined in blood samples collected on d
-17, -7, 0, 3, and at both pregnancy diagnoses
(pregnant cows only) to determine cycling
status, luteolysis, and potential differences in CL
function after AI.

Experiment 2
Cows were stratified by days postpartum and
body condition score and randomly assigned to
one of four treatments: 1) received 100 ig
GnRH and a CIDR insert (d -7), followed in 7 d
by 25 mg PGF2a and CIDR removal (d 0),
followed in 72 h by GnRH and AI (d 3);
(Control; n = 9), 2) same as Control but calves
were removed from their dams for 72 h between
d 0 and d 3 (COCR; n = 9), 3) same as Control
but cow received 400 IU of eCG on d 0 (eCG; n
= 9), 4) same as COCR but cows received an
additional 400 IU of eCG on d 0 (eCGCR; n = 8).
Transrectal ultrasonography and blood sample
collection was performed every 12 h between
PGF and TAI to follow follicle development and
blood concentration of P4 and estradiol. Blood
sample and ultrasonography was performed 7 d









after TAI to measure concentration of P4 in
blood and CL volume.

For both Experiment 1 and 2, the MIXED
procedure of SAS was used to determine if
differences existed for continuous variables:
concentrations of hormones, follicle diameter,
and corpus luteum volume, whereas the
GLIMMIX procedure of SAS was used to
determine difference in binary data of
pregnancy and conception rate.

Results and Discussion
Experiment 1
Pretreatment cycling status differed (P < 0.01)
among locations (locations 1 = 76.5%; 2 =
54.3%; and 3 = 27.4%). For cows having
elevated (>1 ng/mL) P4 at CIDR insert removal,
97.4% had luteolysis, with 17.3% of cows
having low (<1 ng/mL) P4 at insert removal and
at TAI, and 1.2% with increasing P4 from insert
removal to TAI. Progesterone did not differ on d
35 of pregnancy (6.0 0.3 and 6.4 0.4 ng/ml)
or d 67 (6.6 0.4 and 6.4 0.3 ng/ml) for eCG
and Controls, respectively. Unadjusted PR on d
35 was 42.9 vs. 49.8% for eCG vs. controls,
respectively. Herd, cycling status, technician,
and treatment influenced PR. Cycling cows were
1.5 times more (P = 0.046) likely to conceive
than non-cycling cows. Control cows were 1.5
times more (P = 0.036) likely to conceive than
those treated with eCG (Table 1). Cows in
location 3 were 1.8 to 3.5 times more (P =
0.004) likely to conceive than cows at other
locations. Pregnancy loss to d 67 did not differ


(P > 0.05) between treatments (3.7 vs. 2.3% for
eCG vs. Controls), respectively.

Experiment 2
The results of follicle diameter, P4
concentration, and CL volume are summarized
in Table 2. Follicle diameter tended to be greater
(P = 0.09) 48 h after PGF for eCG compared to
Control, while COCR and eCGCR were
intermediate (12.9, 13.1, 15.3, and 14.4 mm, for
Control, COCR, eCG and eCGCR,
respectively). Progesterone concentration on d
10 was greater (P < 0.01) for all the treatments
compared with Control (Figure 2). Corpus
luteum volume was greater (P < 0.05) on d 10
for eCGCR compared with Control and COCR
(3.8 vs 2.1 vs 1.6 cm3, respectively) while eCG
was intermediate (2.9 0.5 cm3) but also greater
(P < 0.05) than Control (Figure 3). Estradiol
concentration was greater (P < 0.05) for eCG
treatment compared with Control and eCGCR at
24 h (1.5 vs 0.5 vs 0.9 pg/ml, respectively) and
36 h (1.5 vs 0.4 vs 0.6 pg/ml, respectively) while
COCR was intermediate (1.1 and 1.0 pg/ml, at
24 and 23 h, respectively; Figure 4). Our data
from Experiment 1 demonstrate that 400 IU of
eCG injected at time of CIDR insert removal did
not improve pregnancy rates. Experiment 2
demonstrated that eCG increased estradiol blood
concentration during the first 36 h after injection
compared with the other treatments except from
COCR. Injection of eCG tended to increase
follicle diameter 48 h later and also elevated P4
concentration in serum and CL volume 7 d after
ovulation.


Literature Cited
Baruselli et al.. 2003. Theriogenology 59:214.
Bergamashci et al. 2005. In: Anais do Congresso Latinoamericano de Buiatria 23; Jornadas Chilenas de
Buitria 7, 2005, Valdivia, Chile, pp 154.


Acknowledgements
We thank Pfizer Animal Health (New York, NY) for contributions of prostaglandin F2, (Lutalyse) and
CIDR inserts and IVX Animal Health (St. Joseph, MO) for donation of gonadotropin-releasing hormone
(OvaCyst). Appreciation also is expressed to Olivia Helms, Don Jones, Mary Maddox, Harvey
Standland, and David Thomas, for their assistance with data collection and laboratory analysis.












eCG TAI &
PGF GnRH


us us


r 'IG


eCG
PGF

4 h- .


0 3

w w


1 is--


10 30 205

W W


us = Ultrasound


0 Blood sample


W = calf weight


CR = Calf removal


Figure 1. Schematic of experimental design for cows treated with or without eCG (eCG
and Control, Exp. 1 and 2) and with or without eCG CR (eCGCR and COCR, Exp. 2).


COCR


eCG


eCGCR


Treatments



Figure 2. Concentration of progesterone (P4) on d 10 associated with cows assigned to one
of four eCG or calf removal treatments on d 0. (Exp. 2) *Means differ (P < 0.01).


Treatments


GnRH


Control
eCG


COCR
eCGCR


Days of -14
treatment






























0 -


CO COCR eCG


eCGCR
eCGCR


Treatments

Figure 3. Corpus luteum (CL) volume on d 10 associated with cows assigned to one of four
eCG or calf removal treatments on d 0. (Exp. 2) abcMeans differ (P < 0.05).


_L













1.4 -


1.2 -


1.0 -


0.8 -


0.6 -


Control CO
......o COCR
------- eCG
-.---- eCGCR


0.4 Y


0.2 1
0 24 36 48 60 72

Hours relative to eCG treatment


Figure 4. Concentration of estradiol relative to hours after treatment with or without eCG and/or calf
removal (CR; Exp. 2). *Means differ (P < 0.05).

Table 1. Pregnancy rates and pregnancy loss in cows after fixed-time artificial insemination and
either no treatment (Control) or treatment with 400 IU of eCG at CIDR removal (eCG;
Experiment 1).
Treatment Pregnancy rate' Pregnancy loss2
------------ ---------
eCG 42.9 3.7
Control 49.8x 2.3


xControl cows were 1.5 times more (P = 0.004; 95% CI
cows.
1Detected on d 35 post-timed AI.
2Between d 35 and 67 of pregnancy.


1.1 to 5.6) likely to conceive than eCG


Table 2. Follicle diameter, concentrations of progesterone (P4), and corpus luteum (CL) volume
relative to equine chorionic gonadotropin (eCG) or 72-h temporary calf removal treatments
(Experiment 2).

Treatment with or without eCG or CR on d 01
Item Control COCR eCG eCGCR
Follicle diameter d 2, mm 12.9 + 0.9v 13.1 0.9w 15.3 + 0.9w 14.4 + 1.0w
P4 on d 10, ng/ml 1.4 + 0.4x 2.7 0.4y 2.7 0.4y 2.8 0.4y
CL volume on d 0, cm3 2.1 0.6xy 1.6 + 0.4xz 2.9+ 0.5yz 3.8 + 0.5y
1CR = 72-hour temporary calf removal; eCG = treatment with 400 IU equine chorionic
gonadotropin at CIDR removal; eCGCR = 72-hour temporary calf removal and treatment with 400
IU equine chorionic gonadotropin at CIDR removal.
w Tendency for diameter or volume to differ (P = 0.10).
xyz Means within a row differ (P < 0.05).


~---------`--T




Full Text

PAGE 1

Summary Two experiments were conducted to evaluate whether eCG at the time of PGF injection had an effect on estradiol concentration in blood, dominant follicle diameter at timed artificial insemination (TAI) concentrations of progesterone (P4) and corpus luteum (CL) volume 7 d after TAI, and improves pregnancy rate s. In Experiment 1, suckled beef cows (n = 513; pure and crossbred Angus, Simmental, and Hereford) were enrolled in a 7 d CO Synch releasing hormone [GnRH] at controlled internal drug release device [CIDR] insertion [d 7]; 25 mg prostaglandin F [PGF] at CIDR after PGF [d 3]) at three locations. Cows were randomly assigned to be controls or receive eCG (400 IU) at the time of PGF injection and CIDR insert removal. Pregnancy w as diagnosed by transrectal ultrasonography at median d 35 and 67 after TAI. Serum P4 concentration was determined in blood samples collected on d 17, 7, 0, 3, and at both pregnancy diagnoses (pregnant cows only) to determine cycling status, luteolysis, and potential differences in CL function after TAI. Unadjusted pregnancy rates (PR) on d 35 was 42.9 vs. 49.8% for eCG vs. controls, respectively. Cycling cows were 1.5 times more (P = 0.05) likely to conceive than noncycling cows. Control cows were 1.5 t imes more (P = 0.04) likely to conceive than those treated with eCG In Experiment 2, 35 cows were stratified by days postpartum and body condition score (BCS) and assigned to one of four treatments. Treatment 1 (control, CO; n = 9) and 2 (eCG; n = 9) were the same as described in Experiment 1; treatment 3 (COCR; n = 9) w as the same as CO but calves were temporarily removed for 72 h between PGF and TAI; treatment 4 (eCGCR; n = 8) was the same as treatment 3 plus an additional injection of eCG (400 IU) was given at the time of CIDR removal. Ultrasonography was performed on d 0, 3, and 10 to evaluate follicle development and ovulation, CL regression between d 0 and 3 and CL volume on d 10. Blood samples were collected on d 0, 3, and 10 to measure P4 concentrations. Blood samples were collected every 12 h between d 0 and 3 to measure estradiol concentration in blood. Progesterone concentration on d 10 was greater (P < 0.01) for all the treatments compared with CO (1.4 vs 2.7 vs 2.7 and 2.8 ng/ml for CO, COCR, eCG, and eCGCR respectively). Follicle diameter tended (P = 0.09) to be greater for eCG than CO 48 h after eCG injection while COCR and eCGCR were intermediate (12.9, 13.1, 15.3, and 14.4 mm, for CO, COCR, eCG and eCGCR, respectively). Corpus luteum volume was greater (P < 0.05) on d 10 for eCGCR compared with CO and COCR ( 3.8 vs 2.1 vs 1.6 cm 3 for eCGCR, CO and COCR respectively) Fixed Time Artificial Insemination (TAI) in Suckled Beef Cows in Response to Equine Chorionic Gonadotropin (eCG) Guilherme Marquezini 1 Vitor Mercadante 1 Logan Wallace 2 Stacey Pulley 2 KC Olson 2 Jon Jaeger 2 Kalyn Bischoff 1 Tera Loyd 1 Jeff Stevenson 2 G. Cliff Lamb 1 Administration of equine chorionic gonadotropin (eCG) at the time of prostaglandin (PGF) and CIDR removal of the CO synch + CIDR protocol does not enhance pregnancy rates. Administration of eCG tended to increase follic le diameter at the time of insemination and increased progesterone concentration and corpus luteum volume seven days after AI. 1 North Florida Research and Education Center, University of Florida Marianna, FL 2 Department o f Animal Sciences and Industry Kansas State University, Manhattan, KS

PAGE 2

while eCG was intermediate (2.9 0.5 cm 3 ) but also greater (P < 0.05) than COCR. Estradiol concentration was greater (P < 0.05) for eCG treatment compared with control and eCGCR at 24 h (1.5 v s 0.5 vs 0.9 pg/ml, respectively) and 36 h (1.5 vs 0.4 vs 0.6 pg/ml, respectively) while COCR was intermediate (1.1 and 1.0 pg/ml, at 24 and 36 h, respectively). We conclude that eCG tended to increase dominant follicle diameter at TAI and increase concent rations of P4 and CL volume 7 d after TAI, however it did not improve pregnancy rates. Introduction Evidence exists that eCG and estradiol administration are important for a desirable pregnancy outcome in protocols for anestrous cows. Because no legal es trogen product is available in the U.S. market for use in cattle, we believed we could duplicate the estrogen effect by administering an appropriately small dose of eCG during the latter part of follicular maturation to stimulate more estradiol biosynthesi s without inducing follicular proliferation (super ovulation). We hypothesized that administering a small dose of eCG would stimulate greater estradiol secretion associated with follicular maturation that would mimic the pro fertility effects of estradiol administration in beef cows. Support for this hypothesis is founded in studies where 400 IU of eCG were administered to cattle at the time of progesterone insert removal and ovulation was induced by estradiol benzoate before timed AI (Baruselli et al., 200 3). Pregnancies per AI were increased in response to eCG (38.9 vs. 54.7%). Their hypothesis was that increased fertility resulted from stimulated luteal function in the CL that resulted from ovulation of follicles exposed to eCG. Using a similar protocol, it was reported that despite a similar sized preovulatory follicle, both the CL size and concentrations of progesterone in blood plasma post estrus were increased after eCG (Bergamaschi et al., 2005). The effects on eCG on circulating concentrations of est radiol were not quantified, but were likely increased in response to eCG stimulated estradiol biosynthesis by the dominant follicle. Therefore, potentially increasing concentrations of estradiol by eCG administration after dominant follicle selection and n ear the time of induced luteolysis may duplicate the profertility effects in lactating cows that have been demonstrated by administering estrogen 24 to 36 h after induced luteolysis. The objective of Experiment 1 was to evaluate if eCG administered at time of PGF and CIDR insert removal will improve pregnancy rates in suckled beef cows. The objective of Experiment 2 was to evaluate if eCG would alter follicle diameter at the time of insemination and increases concentrations of P4 and CL volume seven days af ter timed AI. Materials and Methods Experiment 1 Suckled beef cows (n = 513; pure and crossbred Angus, Simmental, and Hereford) were enrolled in a 7 d CO GnRH at CIDR insertion [d 7]; 25 mg PGF GnRH at AI 66 h after PGF [d 3]) at three locations. Cows were randomly assigned to be Controls or receive eCG (400 IU im) at the time of PGF injection and CIDR insert removal (Figure 1). Pregnancy was diagnosed by transrectal ultrasonography at median d 35 and 67 after AI. Serum P4 concentration (ng/mL) was determined in blood samples collected on d 17, 7, 0, 3, and at both pregnancy diagnoses (pregnant cows only) to determine cycling status, luteolysis, and poten tial differences in CL function after AI. Experiment 2 Cows were stratified by days postpartum and body condition score and randomly assigned to one of four treatments: 1) received 100 g GnRH and a CIDR insert (d 7), followed in 7 d IDR removal (d 0), followed in 72 h by GnRH and AI (d 3); (Control; n = 9), 2) same as Control but calves were removed from their dams for 72 h between d 0 and d 3 (COCR; n = 9), 3) same as Control but cow received 400 IU of eCG on d 0 (eCG; n = 9), 4) sam e as COCR but cows received an aditional 400 IU of eCG on d 0 (eCGCR; n = 8). Transrectal ultrasonography and blood sample collection was performed every 12 h between PGF and TAI to follow follicle development and blood concentration of P4 and estradiol. B lood sample and ultrasonography was performed 7 d

PAGE 3

after TAI to measure concentration of P4 in blood and CL volume. For both Experiment 1 and 2, the MIXED procedure of SAS was used to determine if differences existed for continuous variable s: concentrat ions of hormones, follicle diameter, and corpus luteum volume, whereas the GLIMMIX procedure of SAS was used to determine difference in binary data of pregnancy and conception rate. Results and Discussion Experiment 1 Pretreatment cycling status differed ( P < 0.01) among locations (locations 1 = 76.5%; 2 = 54.3%; and 3 = 27.4%). For cows having elevated (>1 ng/mL) P4 at CIDR insert removal, 97.4% had luteolysis, with 17.3% of cows having low (<1 ng/mL) P4 at insert removal and at TAI, and 1.2% wit h increasing P4 from insert removal to TAI. Progesterone did not differ on d 35 of pregnancy (6.0 0.3 and 6.4 0.4 ng/ml) or d 67 (6.6 0.4 and 6.4 0.3 ng/ml) for eCG and Controls, respectively. Unadjusted PR on d 35 was 42.9 vs. 49.8% for eCG vs. co ntrols, respectively. Herd, cycling status, technician, and treatment influenced PR. Cycling cows were 1.5 times more ( P = 0.046) likely to conceive than non cycling cows. Control cows were 1.5 times more ( P = 0.036) likely to conceive than those treated w ith eCG (Table 1). Cows in location 3 were 1.8 to 3.5 times more ( P = 0.004) likely to conceive than cows at other locations. Pregnancy loss to d 67 did not differ ( P > 0.05) between treatments (3.7 vs. 2.3% for eCG vs. Controls), respectively. Experiment 2 The results of follicle diameter, P4 concentration, and CL volume are summarized in Table 2. Follicle diameter tended to be greater ( P = 0.09) 48 h after PGF for eCG compared to Control, while COCR and eCGCR were intermediate (12.9, 13.1, 15.3, and 14.4 mm, for Control, COCR, eCG and eCGCR, respectively). Progesterone concentration on d 10 was greater ( P < 0.01) for all the tre atments compared with Control (Figure 2). Corpus luteum volume was greater ( P < 0.05) on d 10 for eCGCR compared with Control and COCR (3.8 vs 2.1 vs 1.6 cm 3 respectively) while eCG was intermediate (2.9 0.5 cm 3 ) but also greater ( P < 0.05) than Control (Figure 3). Estradiol concentration was greater ( P < 0.05) for eCG treatment compared with Control and eCGCR at 24 h (1.5 vs 0.5 vs 0.9 pg/ml, respectively) and 36 h (1.5 vs 0.4 vs 0.6 pg/ml, respectively) while COCR was intermediate (1.1 and 1.0 pg/ml, a t 24 and 23 h, respectively; Figure 4). Our data from Experiment 1 demonstrate that 400 IU of eCG injected at time of CIDR insert removal did not improve pregnancy rates. Experiment 2 demonstrated that eCG increased estradiol blood concentration during th e first 36 h after injection compared with the other treatments except from COCR. Injection of eCG tended to increase follicle diameter 48 h later and also elevated P4 concentration in serum and CL volume 7 d after ovulation. Literature Cited Baruselli et al.. 2003. Theriogenology 59:214. Bergamashci et al. 20 05. In: Anais do Congresso Latinoamericano de Buiatria 23; Jornadas Chilenas de Buitria 7, 2005, Valdivia, Chile, pp 154. 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 Olivia Helms, Don Jones, Mary Maddox, Harvey Standland, and David Thomas, for their assistance with data collection and laboratory analysis.

PAGE 4

Figure 1. Schematic of experimental design for cows treated with or without eCG (eCG and Control, Exp. 1 and 2) and with or without eCG CR (eCGCR and COCR, Exp. 2). Figure 2. Concentration of progesterone (P4) on d 10 associated with cows assigned to one of four eCG or calf removal treatments on d 0. (Exp. 2) Means differ ( P < 0.01).

PAGE 5

Figure 3. Corpus luteum (CL) volume on d 10 associated with cows assigned to one of four eCG or calf removal treatments on d 0. (Exp. 2) abc Means differ ( P < 0.05).

PAGE 6

Figure 4. Concentration of estradiol relative to hours after treatment with or without eCG and/or calf removal (CR; Exp. 2). *Means differ (P < 0.05). Table 1 Pregnancy rates and pregnancy loss in cows after fixed time artificial insemination and either no treatment (Control) or treatment with 400 IU of eCG at CIDR removal (eCG; Experiment 1). Treatment Pregnancy rate 1 Pregnancy loss 2 --------% --------eCG 42.9 3.7 Control 49.8 x 2.3 x Control cows were 1.5 times more ( P = 0.004; 95% CI = 1.1 to 5.6) likely to conceive than eCG cows. 1 Detected on d 35 post timed AI. 2 Between d 35 and 67 of pregnancy. Table 2. Follicle diameter, concentrations of progesterone (P4), and corpus luteum (CL) volume relative to equine chorionic gonadotropin (eCG) or 72 h temporary calf removal treatments (Experiment 2). Treatment with or without eCG or CR on d 0 1 Item Control COCR eCG eCGCR Follicle diameter d 2, mm 12.9 0.9 v 13.1 0.9 vw 15.3 0.9 w 14.4 1.0 vw P4 on d 10, ng/ml 1.4 0.4 x 2.7 0.4 y 2.7 0.4 y 2.8 0.4 y CL volume on d 0, cm 3 2.1 0.6 xy 1.6 0.4 xz 2.9 0.5 yz 3.8 0.5 y 1 CR = 72 hour temporary calf removal; eCG = treatment with 400 IU equine chorionic gonadotropin at CIDR removal; eCGCR = 72 hour temporary calf removal and treatment with 400 IU equine chorionic gonadotropin at CIDR removal. vw Tendency for diameter or volu me to differ ( P = 0.10). xyz Means within a row differ ( P < 0.05).