Effects of day of cycle at initiation of a select synch/CIDR + timed-artificial insemination protocol in suckled Angus a...

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Effects of day of cycle at initiation of a select synch/CIDR + timed-artificial insemination protocol in suckled Angus and Brangus cows
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2009 Florida Beef Report
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Esterman, Regina
Austin, Brad
Woodall, Steaven
McKinniss, Erin
Yelich, Joel
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Institute of Food and Agricultural Sciences, University of Florida
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Gainesville, Fla.
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Effects of Day of Cycle at Initiation of a Select Synch/CIDR + Timed-artificial
Insemination Protocol in Suckled Angus and Brangus Cows

Regina Esterman1
Brad Austin
Steaven Woodall
Erin McKinniss
Joel Yelich


Summary
Postpartum Angus (n=37) and Brangus (n=37)
cows were used to evaluate cycling status and
day of estrous cycle (DOC) effects at initiation
of a Select Synch/CIDR + timed artificial
insemination (AI) protocol on ovulation rate,
follicle development, and pregnancy rates. The
experiment was conducted in two phases (phase
1 anestrous, phase 2=estrous cycling).
Anestrous cows were selected to have either
ovulated to GnRH on d 0 (n 6 Angus, n 6
Brangus) or not ovulated to GnRH on d 0 (n=6
Angus, n=6 Brangus). Estrous cycling cows
were pre-synchronized to be d 2, 6, 10, 14, and
18 DOC on d 0 of synchronization (Angus 5;
Brangus=5 per DOC group). In phase 1,
anestrous cows had similar (P>0.05) ovulatory
follicle sizes for Angus (12.7 0.7 mm) and
Brangus (13.7 0.7 mm). Total ovulation rate
following PGF2, was similar (P>0.05) for Angus
(83.3%) and Brangus (91.7%), as well as for
cows that ovulated to GnRH (91.7%) and failed
to ovulate to GnRH (83.8%). Estrous response
(ER) tended (P=0.17) to be greater for Brangus
(41.7%) compared to Angus (16.7%). Cows
that ovulated to GnRH also tended (P=0.17) to
have a greater ER compared to cows that failed


to ovulated to GnRH (16.7%). Conception rate
(CR) was similar (P>0.05) for Angus (50.0%)
and Brangus (40.0%) cows, but cows that
ovulated to GnRH (60.0%) tended (P=0.09) to
have a greater CR compared to cows that failed
to ovulate to GnRH (0.0%). Timed-AI
pregnancy rate (TAIPR) was similar (P>0.05)
for Angus (30.0%) and Brangus (42.9%), but
TAIPR tended (P=0.11) to be greater for cows
that failed to ovulate to GnRH (50.0%)
compared to cows that ovulated to GnRH
(14.3%). Synchronized pregnancy rates were
similar (P>0.05) for both Angus (33.3%) and
Brangus (41.7%), as well as for cows that
ovulated to GnRH (33.3%) and failed to ovulate
to GnRH (41.7%). In phase 2, breed had no
effect (P>0.05) on ovulation rate to GnRH
(Angus=56%; Brangus 522%) and ovulatory
follicle size on d 0 (Angus 13.9 1.8 mm;
Brangus=14.1 2.4 mm). Day of cycle affected
(P<0.05) ovulation rate to GnRH and ovulatory
follicle size. Estrous response was greater
(P<0.05) for Brangus (48%) compared to Angus
(28%), but CR, TAIPR, and SPR were similar
(P>0.05) for Angus and Brangus. However,
DOC affected (P<0.05) ER, CR, TAIPR, and


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In anestrous cows, synchronized pregnancy rates were similar for Angus and Brangus cows, as well as for
cows that ovulated to GnRH on d 0 and cows that failed to ovulate to GnRH on d 0. In estrous cycling
cows, day of the estrous cycle at initiation of the Select Synch/CIDR + timed-artificial insemination
protocol affected ovulation rate and ovulatory follicle sizes on d 0, estrous response, conception rate,
timed-AI pregnancy rate, and synchronized pregnancy rate. Synchronized pregnancy rates were similar
for both anestrous and estrous cycling cows, regardless of whether they ovulated to GnRH on d 0 or failed
to ovulate to GnRH on d 0 of the synchronization protocol.










SPRfor DOC groups.

Introduction
Inclusion of GnRH at the start of a
synchronization protocol causes ovulation of
follicles greater than 10 mm in diameter. By
ovulating the largest follicle present, the cow
will begin a new wave of follicle growth. With
a new wave of follicle growth, follicle
development can be better synchronized within a
group of cows. By synchronizing both follicle
development and luteal lifespan (using PGF2a), a
more synchronous estrus can be achieved
following PGF2, administration.

Due to differences in a cow's length of estrous
cycle and number of follicular waves, predicting
when GnRH will be most effective can be a
challenge. GnRH is effective once a dominant
follicle reaches 10 mm in diameter and
continues until the follicle either ovulates on its
own or becomes atretic and regresses in
preparation for the next follicular wave. Across
all stages of the estrous cycle, it is estimated that
60 to 70% of Bos taurus cows will ovulate to
GnRH. Cattle of Bos indicus breeding are
known to frequently have a greater number of
follicular waves and more variability to their
length of estrous cycle. With greater numbers of
follicular waves, the windows of opportunity for
GnRH to be effective are shortened. However,
recent research from our lab would suggest that
ovulation rates in cattle of Bos indicus breeding
are at or slightly below that of Bos taurus cattle.

Therefore, the objectives of this experiment
were to: 1) evaluate follicle development
following ovulation or no ovulation to GnRH in
anestrous Angus and Brangus cows, 2) evaluate
luteolysis, estrous characteristics, and pregnancy
rates following ovulation or no ovulation to
GnRH in anestrous Angus and Brangus cows, 3)
determine ovulation rates to GnRH in cycling
Angus and Brangus cows known to be on d 2, 6,
10, 14, & 18 of their estrous cycles, and 4)
evaluate luteolysis, estrous characteristics, and
pregnancy rates following the Select
Synch/CIDR + timed-AI protocol in cycling
Angus and Brangus cows known to be on d 2, 6,
10, 14, & 18 of their estrous cycles.


Materials & Methods
The experiment was conducted from March to
June of 2007 at the University of Florida,
Department of Animal Sciences, Santa Fe Beef
Research Unit in two phases (phase l=anestrous,
phase 2=estrous cycling). Postpartum lactating
Angus (n=37) and Brangus (n=37) cows were
utilized. For the first phase of the experiment,
on d -12 and -2 blood samples were collected for
the evaluation of progesterone concentrations to
determine estrous cycling status. A cow was
deemed to have estrous cycles (cycling) if either
sample had progesterone concentrations > 1
ng/mL, and anestrous (noncycling) if
progesterone concentrations were < 1 ng/mL at
both samples. Only cows determined to be
anestrous were utilized for the first phase of the
experiment. Day 0 was designated as the start of
the synchronization protocol. At the start of
phase 1 synchronization, Angus and Brangus
cows, respectively, were 2 yr of age, body
weight 1,038 31 lb and 1,025 31 lb, body
condition score (1=emaciated, 9=obese) 5.0 +
0.1 and 5.2 0.1, and 72.0 4.6 d and 61.5
4.6 d. For phase 2, Angus and Brangus cows,
respectively, were 5.3 2.4 y and 3.6 1.1 y of
age, body weight 1,192 95 lb and 1,188 139
lb, body condition score 5.3 0.4 and 5.4 0.5,
and d postpartum 59.2 2.4 d and 54.7 11.1 d.

In phase 1 (anestrous cows), on d 0 of the
experiment, all cows received GnRH (100 Gg;
i.m., Cystorelin, Merial) and a new CIDR (1.38
g; Eazi-BreedTM CIDR, Pfizer Animal Health).
On d 2, ovulation status to GnRH was evaluated
and cows that ovulated to GnRH (n=6) and cows
that failed to ovulate to GnRH (n=6) within each
breed group were selected to continue on the
experiment. On d 7, the CIDR was removed
and cows received PGF2. (25 mg, i.m.,
Lutalyse, Pfizer Animal Health).

In phase 2 estrouss cycling cows), cows were
pre-synchronized using a 7 d CIDR with PGF2a
on d 7 to be on either d 2, 6, 10, 14, or 18 of
their estrous cycle (DOC) at the start of
synchronization. Following PGF2, in the pre-
synchronization, estrous was detected visually
with the aid of estrous detection patches
(EstrotectTM, Rockway, Inc.) and the day each
cow displayed estrus was determined to be d 0


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of that cow's estrous cycle. Pre-synchronization
groups were staggered over several weeks prior
to the synchronization in order for all cows to
began the synchronization on the same day. On
d 0 of synchronization, all cows received GnRH
and a new CIDR. On d 7, the CIDR was
removed and cows received PGF2a.

Following PGF2a in both phases, estrus was
monitored using electronic heat detection
monitors (HeatWatch, DDx) for 3 d. Cows
were inseminated by a single AI technician 8 to
12 h after declared in estrus by the HeatWatch
system. Cows were inseminated using frozen-
thawed semen from multiple sires.

The GENMOD procedure of SAS (SAS Inst.
Inc.) was used for the statistical analysis of
categorical data. The effect of breed, DOC, and
their interaction were evaluated for ovulation
rate to GnRH, estrous response, conception rate,
timed-AI pregnancy rate, and synchronized
pregnancy rate, while cow age, DPP, BCS, and
interval from PGF2, to the onset of estrus were
included as covariates. The effect of ovulation
or no ovulation to GnRH, breed, and interaction
were evaluated for estrous response, conception
rate, timed-AI pregnancy rate, and synchronized
pregnancy rate, while cow age, DPP, BCS, and
interval from PGF2~ to the onset of estrus were
included as covariates. When covariates were
significant (P < 0.05) they were treated as
independent variables. The effect of breed,
DOC, and the interaction on follicle diameters
were analyzed using GLM procedure of SAS.

Results
In phase 1 (anestrous cows), ovulatory follicle
size in response to GnRH on d 0 for cows that
ovulated was 13.2 0.5 mm. Ovulatory follicle
size was similar (P>0.05) for Angus (12.7 0.7
mm) and Brangus (13.7 0.7 mm) cows.

Luteal regression was 100% for both Angus and
Brangus and cows, as well as 100% for cows
that ovulated to GnRH on d 0. Estrous response
tended (P=0.17) to be greater for Brangus
compared to Angus (Table 1). Estrous response
also tended (P=0.17) to be greater for cows that
ovulated to GnRH on d 0 compared to cows that
did not ovulate to GnRH on d 0. Interval from


PGF2~ to the onset of estrus was similar
(P>0.05) for Angus and Brangus cows.
However, cows that ovulated to GnRH on d 0
had a greater (P<0.05) interval from PGF2, to
the onset of estrus compared to cows that did not
ovulate to GnRH on d 0. Duration of estrus
tended (P=0.06) to be longer for Angus cows
compared to Brangus cows, but duration of
estrus was similar (P>0.05) whether cows
ovulated or did not ovulate to GnRH on d 0.
The number of mounts received during estrus
was similar (P>0.05) for Angus and Brangus
cows. Cows that ovulated to GnRH on d 0
tended (P=0.13) to receive more mounts (34.2)
compared to cows that did not ovulate to GnRH
(21.5).


Conception rate was similar (P>0.05) for Angus
and Brangus cows (Table 2). Cows that
ovulated to GnRH on d 0 tended (P=0.09) to
have a greater conception rate (60.0%; 3/5)
compared to cows that did not ovulate to GnRH
on d 0 (0%; 2/2). Timed-AI pregnancy rate was
similar (P>0.05) for Angus and Brangus cows
(Table 2), but cows that ovulated to GnRH on d
0 tended (P=0.11) to have a lower timed-AI
pregnancy rate compared to cows that did not
ovulate to GnRH on d 0 (14.3%; 1/7 and 50.0%;
5/5, respectively). Synchronized pregnancy rate
was similar (P>0.05) for Angus and Brangus
cows, as well as for cows that ovulated or failed
to ovulate to GnRH on d 0 (Table 2).

In phase 2 estrouss cycling), ovulation rate to
GnRH on d 0 was similar (P>0.05) between
Angus and Brangus cows (Table 3). Day of the
estrous cycle effected (P<0.05) ovulation rate to
GnRH. No cows (0/10) that were on d 2 of their
estrous cycle at the start of synchronization
ovulated to GnRH on d 0. Cows on d 6, 10, 14,
& 18 of their estrous cycles had ovulation rates
to GnRH of 100, 30, 70 and 70%, respectively.
Size of the follicle ovulated to GnRH on d 0 was
similar (P>0.05) for Angus (13.9 mm) and
Brangus (14.1 mm) cows. However, cows on
DOC 6 and 14 ovulated smaller (P<0.05)
follicles to GnRH compared to cows on DOC 10
or 18.


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Luteal regression following PGF2a was similar
(P>0.05) for both Angus (92.0%; 23/25) and
Brangus (92.0%; 23/25) cows. Luteolysis was
100% for cows DOC 10, 14, and 18, but was
lower (P<0.05) for cows DOC 2 and 6 (both
80%). Ovulation rate following PGF2a was
similar (P>0.05) for Angus (88.0%; 22/25) and
Brangus (92.0%; 23/25). Ovulation rate
following PGF2a tended (P=0.12) to be different
between DOC groups with ovulation rates of
70.0, 90.0, 90.0, 100.0, and 100.0% for cows
DOC 2, 6, 10, 14, and 18, respectively.
Ovulatory follicle size following PGF2a was
similar (P>0.05) for Angus (15.0 + 0.6 mm) and
Brangus (15.3 0.6 mm) cows. However, DOC
tended (P=0.06) to effect ovulatory follicle size
following PGF2,. Ovulatory follicle size
following PGF2, was similar (P>0.05) for DOC
2 (13.6 0.9 mm), 6 (14.1 0.8 mm), 10 (15.0
0.8 mm), and 14 (15.4 0.8 mm). Ovulatory
follicle size was greater (P<0.05) for DOC 18
(16.9 + 0.8 mm) compared to DOC 2 and 4, but
was similar (P>0.05) to DOC 10 and 14.

Estrous response was greater (P<0.05) for cows
that ovulated to GnRH on d 0 (48.7%; 19/39)
compared to cows that failed to ovulate to
GnRH on d 0 (20.0%; 7/35). Estrous response
was greater (P=0.05) for Brangus compared to
Angus cows (Table 4). Estrous response was
different (P<0.05) for DOC groups. Interval
from PGF2, to the onset of estrus was similar
(P>0.05) for Angus and Brangus cows, but
tended (P=0.11) to be different for DOC groups.
Duration of estrus tended (P=0.12) to be greater
for Brangus cows (11 h 15 m) compared to
Angus cows (8 h 46 m). Duration of estrus was
similar (P>0.05) for DOC groups. Brangus
cows received a greater (P<0.05) number of
mounts during estrus (53.9) compared to Angus
cows (20.3). Number of mounts received during
estrus was similar (P>0.05) for DOC groups.


Cows that ovulated to GnRH on d 0 (47.4%;
9/19) had similar (P>0.05) conception rates
compared to cows that failed to ovulate to
GnRH on d 0 (57.1%; 4/7). Conception rates
were similar (P>0.05) for Angus compared to
Brangus cows (Table 5). Conception rate was
effected (P<0.05) by DOC. Timed-AI
pregnancy rates were similar (P>0.05) for
Angus and Brangus cows. Timed-AI pregnancy
rate was effected (P<0.05) by DOC. Cows that
failed to ovulate to GnRH on d 0 (42.9%; 12/28)
tended (P=0.09) to have a greater timed-AI
pregnancy rate compared to cows that ovulated
to GnRH on d 0 (20.0; 4/20). Synchronized
pregnancy rate was similar (P>0.05) for Angus
and Brangus cows. Cows 2, 6, and 18 DOC had
similar (P>0.05) synchronized pregnancy rates,
but were lower (P<0.05) compared to cows 10
and 14 DOC. However, cows 10, 14, and 18
DOC were similar (P>0.05) to each other.
Synchronized pregnancy rates were similar
(P>0.05) for cows that ovulated to GnRH on d 0
(33.3%; 13/39) and cows that failed to ovulate to
GnRH on d 0 (45.7%; 16/35).

In conclusion, DOC when a Select Synch/CIDR
+ timed-AI synchronization protocol is initiated
affected ovulation rates to GnRH and ovulatory
follicle size to GnRH on d 0. Cows that
ovulated to GnRH on d 0 and cows that failed to
ovulate to GnRH on d 0 had similar
synchronized pregnancy rates. Estrous response,
conception rate, timed-AI pregnancy rate, and
synchronized pregnancy rate were influenced by
DOC.


'Regina Esterman, Graduate Student; Brad Austin, Graduate Student; Steaven Woodall, Former
Graduate Student; Erin McKinniss, Graduate Student; Joel Yelich; Associate Professor, UF-IFA,
Department of Animal Sciences, Gainesville, FL


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Table 1. Effect of breed and ovulation status to GnRH on d 0 (OVGnRH) on estrous characteristics
following PGF2, in anestrous Angus and Brangus cows synchronized with a Select Synch + CIDR and
timed-AI synchronization protocol.a


Estrous Interval from Duration of Total mounts
Variable n response, %b PGF2, to onset of estrus (hr, min)d during estruse
estrus (hr, min)'

Angus 12 16.7(12) 49 h 5 m 3 h 16 h 20 m 3 h 32 7.6
44m 53m
12 41.7(12) 49h6m 2h 5h21m+2h 30 4.8
Brangus 21m 27 m



OVto 12 41.7(12) 51 h 16 m h 6h8m 3 h 34.2 3.8
GnRH 30m m
No OVto 12 16.7(12) 43 h 40m 2 h 14 h 20m 4 h 21.5 6.0
GnRH 22 m 46 m
P values

Breed P = 0.17 P > 0.05 P = 0.06 P > 0.05

OVGnRH P = 0.17 P = 0.04 P > 0.05 P = 0.13
Breed x OVGnRH P > 0.05 P > 0.05 P = 0.04 P > 0.05

a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF2, administered at the time of
CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to 12
h later. Cows which had not displayed estrus were timed-AI at 76 to 80 h and given GnRH.
b Percentage of cows displaying estrus 3 d after PGF2a of the total treated.

c Time from PGF2a administration to the first mount of estrus, as determined by HeatWatch.
d Time from the first mount of estrus to the last mount of estrus, as determined by HeatWatch
e Total mounting events which occurred during estrus, as determined by HeatWatch.


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Table 2. Effect of breed and ovulation status to GnRH on d 0 (OVGnRH) on estrous response,
conception, timed-AI pregnancy, and synchronized pregnancy rates following PGF2a in anestrous
Angus and Brangus cows synchronized with a Select Synch + CIDR and timed-AI synchronization
protocol.a


Estrous Conception rate, Timed-AI Synchronized
Variable n response, %b % pregnancy rate, pregnancy rate,
%d %e

Angus 12 16.7 (12) 50.0 (12) 30.0 (10) 33.3 (12)


OV to 6 16.7(6) 100.0(1) 0.0(5) 16.7(6)
GnRH

No OV to 6 16.7 (6) 0.0 (1) 60.0 (5) 50.0 (6)
GnRH

12 41.7(12) 40.0(5) 42.9(7) 41.7(12)
Brangus

OV to 6 66.7(6) 50.0(4) 50.0(2) 50.0(6)
GnRH
No OV to 6 16.7(6) 0.0(1) 40.0(5) 33.3 (6)
GnRH
P values

Breed P = 0.17 P > 0.05 P > 0.05 P > 0.05

OVGnRH P = 0.17 P = 0.09 P = 0.11 P > 0.05
Breed x OVGnRH P > 0.05 P > 0.05 P = 0.06 P = 0.19

a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF2, administered at the time of
CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to 12
h later. Cows which had not displayed estrus were timed-AI at 76 to 80 h and given GnRH.
b Percentage of cows displaying estrus 3 d after PGF2, of total treated.
' Percentage of cows pregnant to AI of the total that exhibited estrus and were AI.
d Percentage of cows pregnant to timed-AI of the total that were timed-AI.
e Percentage of cows pregnant during the synchronized breeding of the total treated.


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Table 3. Effect of breed and day of estrous cycle on ovulation rates to GnRH and ovulatory follicle
size (LS mean + SE) in estrous cycling Angus and Brangus cows synchronized with a Select Synch +
CIDR and timed-AI synchronization protocol.a

Follicles ovulating to GnRH, Ovulatory follicle size, mm,
Variable n %b (range)c


Angus 25 56.0(25) 13.9 0.6 (11 to 17)


25 52.0 (25) 14.1 + 0.6 (10 to 18)
Brangus



d2 10 0.0(10)

d 6 10 100.0 (10) 13.2 + 0.6 (11 to 17)d


d 10 10 30.0 (10) 15.7 1.0 (14 to 17)e


d 14 10 70.0 (10) 12.7 + 0.7 (10 to 14)d


d 18 10 70.0 (10) 15.6 + 0.7 (14 to 18)e


P values

Breed P > 0.05 P > 0.05

DOC P < 0.05 P < 0.05
a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF2a administered at the time of
CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to
12 h later. Cows which had not displayed estrus were timed-AI at 76 to 80 h and given GnRH.
b Percentage of cows that ovulated to GnRH on d 11 divided by the total treated.
' Size of the largest follicle on d 0 that ovulated by 48 h later.
d, Means without a common superscript within a column differ (P<0.05).


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Table 4. Effect of breed and day of estrous cycle on estrous characteristics as determined by
HeatWatch of estrous cycling Angus and Brangus cows synchronized with a Select Synch + CIDR
and timed-AI synchronization protocol.a With the exception of estrous response estrous characteristics
are presented as LS means + SE.a

Estrous Interval from Duration of Total mounts
Variable n response, %b PGF2, to onset of estrus (hr, during estruse
estrus (hr, min)' min)d

Angus 25 28.0(25) 49 h 2 m 8 h 46 m 20.3 + 10.4
3h 39 m 1 h 14 m

25 48.0(25) 54h26 m 11 h 15 m 53.9 8.0
S2h 47 m 57m


d2 10 0.0 (10)


d6 10 10.0 (10)g 64 h 24m 12 h 15 m 30.0 31.8
8h 48 mf 3 h 28 m
d 10 10 30.0 (10)g,h 62 h 20 m 11 h38 m 61.7 18.3
5h5mf 2h0m

d 14 10 60.0 (10)hi 50h2m 11 h 18 m 49.7 13.0
3h 35 mfg 1 h 25 m

d 18 10 90.0 (10)' 49 h 26 m 9h3m 30.7 + 10.6
2h 56 mg 1 h9m

P values
Breed P = 0.05 P > 0.05 P = 0.12 P < 0.05

DOC P < 0.01 P = 0.11 P > 0.05 P > 0.05

a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF2, administered at the time of
CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to 12 h
later. Cows which had not displayed estrus were timed-AI at 76 to 80 h and given GnRH.
b Percentage of cows displaying estrus 3 d after PGF2~ of the total treated.

C Time from PGF2~ administration to the first mount of estrus, as determined by HeatWatch.
d Time from the first mount of estrus to the last mount of estrus, as determined by HeatWatch.
e Total mounting events which occurred during estrus, as determined by HeatWatch.
f,g,h,i Means without a common superscript within a column differ (P<0.05).


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Table 5. Effect of breed and day of estrous cycle on estrous response and pregnancy rates in cycling
Angus and Brangus cows synchronized with a Select Synch + CIDR and timed-AI synchronization
protocol.a

Estrous response, Conception rate, Timed-AI Synchronized
Variable n %b %o pregnancy rate, pregnancy rate,
%d %e

Angus 25 28.0 (25) 57.1(7) 38.9 (18) 44.0 (25)

Brangus 25 48.0 (25) 50.0 (12) 23.1(13) 36.0 (25)


d 2 10 0.0 (10) 0.0 (0) 10.0 (10) 10.0 (10)f

d 6 10 10.0 (10) 100.0 (1) 11.1 (9) 20.0 (10)f

d 10 10 30.0 (10) 100.0 (3) 57.1 (7) 70.0 (10)g

d 14 10 60.0 (10) 33.3 (6) 100.0 (4) 60.0 (10)g

d 18 10 90.0 (10) 44.4 (9) 0.0 (1) 40.0 (10)g

P values

Breed P = 0.14 P > 0.05 P > 0.05 P > 0.05

DOC P < 0.05 P < 0.05 P < 0.05 P < 0.05
a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF2a administered at the time of
CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to
12 h later. Cows which had not displayed estrus were timed-AI at 76 to 80 h and given GnRH.
b Percentage of cows displaying estrus 3 d after PGF2a of total treated.
' Percentage of cows pregnant to AI of the total that exhibited estrus and were AI.
d Percentage of cows pregnant to timed-AI of the total that were timed-AI.
e Percentage of cows pregnant during the synchronized breeding of the total treated.
f'g Means without a common superscript within a column differ (P<0.05).


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Effects o f Day o f Cycle a t Initiation o f a Select Synch / CIDR + Timed a rtificial Insemination Protocol i n Suck l ed Angus a nd Brangus Cows Regina Esterman 1 Brad Austin Steaven Woodall Erin McKinniss Joel Yelich Summary Postpartum Angus (n=37) and Brangus (n=37) cows were used to evaluate cycling status and day of estrous cycle (DOC) effects at initiation of a Select Synch/CIDR + timed artificial insemination (AI) protocol on ovulation rate, follicle development, and pregnancy rates. The experiment was conducted in two phases (phase 1=anestrous, phase 2=estrous cycling). Anestrous cows were selected to have either ovulated to GnRH on d 0 (n=6 Angus, n=6 Brangus) or not ovulated to GnRH on d 0 (n=6 Angus, n=6 Brangus). Estrous cycling cows were pre-synchronized to be d 2, 6, 10, 14, and 18 DOC on d 0 of synchronization (Angus=5; Brangus=5 per DOC group). In phase 1, anestrous cows had similar (P>0.05) ovulatory follicle sizes for Angus (12.7 0.7 mm) and Brangus (13.7 0.7 mm). Total ovulation rate following PGF was similar (P>0.05) for Angus (83.3%) and Brangus (91.7%), as well as for cows that ovulated to GnRH (91.7%) and failed to ovulate to GnRH (83.8%). Estrous response (ER) tended (P=0.17) to be greater for Brangus (41.7%) compared to Angus (16.7%). Cows that ovulated to GnRH also tended (P=0.17) to have a greater ER compared to cows that failed to ovulated to GnRH (16.7%). Conception rate (CR) was similar (P>0.05) for Angus (50.0%) and Brangus (40.0%) cows, but cows that ovulated to GnRH (60.0%) tended (P=0.09) to have a greater CR compared to cows that failed to ovulate to GnRH (0.0%). Timed-AI pregnancy rate (TAIPR) was similar (P>0.05) for Angus (30.0%) and Brangus (42.9%), but TAIPR tended (P=0.11) to be greater for cows that failed to ovulate to GnRH (50.0%) compared to cows that ovulated to GnRH (14.3%). Synchronized pregnancy rates were similar (P>0.05) for both Angus (33.3%) and Brangus (41.7%), as well as for cows that ovulated to GnRH (33.3%) and failed to ovulate to GnRH (41.7%). In phase 2, breed had no effect (P>0.05) on ovulation rate to GnRH (Angus=56%; Brangus=52%) and ovulatory follicle size on d 0 (Angus=13.9 1.8 mm; Brangus=14.1 2.4 mm). Day of cycle affected (P<0.05) ovulation rate to GnRH and ovulatory follicle size. Estrous response was greater (P<0.05) for Brangus (48%) compared to Angus (28%), but CR, TAIPR, and SPR were similar (P>0.05) for Angus and Brangus. However, DOC affected (P<0.05) ER, CR, TAIPR, and In anestrous cows, synchronized pregnancy rates were similar for Angus and Brangus cows, as well as for cows that ovulated to GnRH on d 0 and cows that failed to ovulate to GnRH on d 0. In estrous cycling cows, day of the estrous cycle at initiation of th e Select Synch/CIDR + timed artificial insemination protocol affected ovulation rate and ovulatory follicle sizes on d 0, estrous response, conception rate, timed AI pregnancy rate, and synchronized pregnancy rate. Synchronized pregnancy rates were simila r for both anestrous and estrous cycling cows, regardless of whether they ovulated to GnRH on d 0 or failed to ovulate to GnRH on d 0 of the synchronization protocol.

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SPR for DOC groups. Introduction Inclusion of GnRH at the start of a synchronization protocol causes ovulation of follicles greater than 10 mm in diameter. By ovulating the largest follicle present, the cow will begin a new wave of follicle growth. With a new wave of follicle growth, follicle development can be better synchronized within a group of cows. By synchronizing both follicle development and luteal lifespan (using PGF ), a more synchronous estrus can be achieved following PGF administration. cycle and number of follicular waves, predicting when GnRH will be most effective can be a challenge. GnRH is effective once a dominant follicle reaches 10 mm in diameter and continues until the follicle either ovulates on its own or becomes atretic and regresses in preparation for the next follicular wave. Across all stages of the estrous cycle, it is estimated that 60 to 70% of Bos taurus cows will ovulate to GnRH. Cattle of Bos indicus breeding are known to frequently have a greater number of follicular waves and more variability to their length of estrous cycle. With greater numbers of follicular waves, the windows of opportunity for GnRH to be effective are shortened. However, recent research from our lab would suggest that ovulation rates in cattle of Bos indicus breeding are at or slightly below that of Bos taurus cattle. Therefore, the objectives of this experiment were to: 1) evaluate follicle development following ovulation or no ovulation to GnRH in anestrous Angus and Brangus cows, 2) evaluate luteolysis, estrous characteristics, and pregnancy rates following ovulation or no ovulation to GnRH in anestrous Angus and Brangus cows, 3) determine ovulation rates to GnRH in cycling Angus and Brangus cows known to be on d 2, 6, 10, 14, & 18 of their estrous cycles, and 4) evaluate luteolysis, estrous characteristics, and pregnancy rates following the Select Synch/CIDR + timed-AI protocol in cycling Angus and Brangus cows known to be on d 2, 6, 10, 14, & 18 of their estrous cycles. Materials & Methods The experiment was conducted from March to June of 2007 at the University of Florida, Department of Animal Sciences, Santa Fe Beef Research Unit in two phases (phase 1=anestrous, phase 2=estrous cycling). Postpartum lactating Angus (n=37) and Brangus (n=37) cows were utilized. For the first phase of the experiment, on d -12 and -2 blood samples were collected for the evaluation of progesterone concentrations to determine estrous cycling status. A cow was deemed to have estrous cycles (cycling) if either ng/mL, and anestrous (noncycling) if progesterone concentrations were < 1 ng/mL at both samples. Only cows determined to be anestrous were utilized for the first phase of the experiment. Day 0 was designated as the start of the synchronization protocol. At the start of phase 1 synchronization, Angus and Brangus cows, respectively, were 2 yr of age, body weight 1,038 31 lb and 1,025 31 lb, body condition score (1=emaciated, 9=obese) 5.0 0.1 and 5.2 0.1, and 72.0 4.6 d and 61.5 4.6 d. For phase 2, Angus and Brangus cows, respectively, were 5.3 2.4 y and 3.6 1.1 y of age, body weight 1,192 95 lb and 1,188 139 lb, body condition score 5.3 0.4 and 5.4 0.5, and d postpartum 59.2 2.4 d and 54.7 11.1 d. In phase 1 (anestrous cows), on d 0 of the experiment, all cows received GnRH (100 g; i.m., Cystorelin Merial) and a new CIDR (1.38 g; Eazi, Pfizer Animal Health). On d 2, ovulation status to GnRH was evaluated and cows that ovulated to GnRH (n=6) and cows that failed to ovulate to GnRH (n=6) within each breed group were selected to continue on the experiment. On d 7, the CIDR was removed and cows received PGF (25 mg, i.m., Lutalyse Pfizer Animal Health). In phase 2 (estrous cycling cows), cows were pre-synchronized using a 7 d CIDR with PGF on d 7 to be on either d 2, 6, 10, 14, or 18 of their estrous cycle (DOC) at the start of synchronization. Following PGF in the presynchronization, estrous was detected visually with the aid of estrous detection patches cow displayed estrus was determined to be d 0

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re -synchronization groups were staggered over several weeks prior to the synchronization in order for all cows to began the synchronization on the same day. On d 0 of synchronization, all cows received GnRH and a new CIDR. On d 7, the CIDR was removed and cows received PGF Following PGF in both phases, estrus was monitored using electronic heat detection monitors (HeatWatch DDx) for 3 d. Cows were inseminated by a single AI technician 8 to 12 h after declared in estrus by the HeatWatch system. Cows were inseminated using frozenthawed semen from multiple sires. The GENMOD procedure of SAS (SAS Inst. Inc.) was used for the statistical analysis of categorical data. The effect of breed, DOC, and their interaction were evaluated for ovulation rate to GnRH, estrous response, conception rate, timed-AI pregnancy rate, and synchronized pregnancy rate, while cow age, DPP, BCS, and interval from PGF to the onset of estrus were included as covariates. The effect of ovulation or no ovulation to GnRH, breed, and interaction were evaluated for estrous response, conception rate, timed-AI pregnancy rate, and synchronized pregnancy rate, while cow age, DPP, BCS, and interval from PGF to the onset of estrus were included as covariates. When covariates were significant ( P < 0.05) they were treated as independent variables. The effect of breed, DOC, and the interaction on follicle diameters were analyzed using GLM procedure of SAS. Results In phase 1 (anestrous cows), ovulatory follicle size in response to GnRH on d 0 for cows that ovulated was 13.2 0.5 mm. Ovulatory follicle size was similar ( P >0.05) for Angus (12.7 0.7 mm) and Brangus (13.7 0.7 mm) cows. Luteal regression was 100% for both Angus and Brangus and cows, as well as 100% for cows that ovulated to GnRH on d 0. Estrous response tended ( P =0.17) to be greater for Brangus compared to Angus (Table 1). Estrous response also tended ( P =0.17) to be greater for cows that ovulated to GnRH on d 0 compared to cows that did not ovulate to GnRH on d 0. Interval from PGF to the onset of estrus was similar ( P>0.05) for Angus and Brangus cows. However, cows that ovulated to GnRH on d 0 had a greater ( P <0.05) interval from PGF to the onset of estrus compared to cows that did not ovulate to GnRH on d 0. Duration of estrus tended ( P =0.06) to be longer for Angus cows compared to Brangus cows, but duration of estrus was similar ( P >0.05) whether cows ovulated or did not ovulate to GnRH on d 0. The number of mounts received during estrus was similar ( P >0.05) for Angus and Brangus cows. Cows that ovulated to GnRH on d 0 tended ( P =0.13) to receive more mounts (34.2) compared to cows that did not ovulate to GnRH (21.5). Conception rate was similar ( P >0.05) for Angus and Brangus cows (Table 2). Cows that ovulated to GnRH on d 0 tended ( P =0.09) to have a greater conception rate (60.0%; 3/5) compared to cows that did not ovulate to GnRH on d 0 (0%; 2/2). Timed-AI pregnancy rate was similar ( P >0.05) for Angus and Brangus cows (Table 2), but cows that ovulated to GnRH on d 0 tended ( P =0.11) to have a lower timed-AI pregnancy rate compared to cows that did not ovulate to GnRH on d 0 (14.3%; 1/7 and 50.0%; 5/5, respectively). Synchronized pregnancy rat e was similar ( P >0.05) for Angus and Brangus cows, as well as for cows that ovulated or failed to ovulate to GnRH on d 0 (Table 2). In phase 2 (estrous cycling), ovulation rate to GnRH on d 0 was similar ( P>0.05) between Angus and Brangus cows (Table 3). Day of the estrous cycle effected ( P <0.05) ovulation rate to GnRH. No cows (0/10) that were on d 2 of their estrous cycle at the start of synchronization ovulated to GnRH on d 0. Cows on d 6, 10, 14, & 18 of their estrous cycles had ovulation rates to GnRH of 100, 30, 70 and 70%, respectively. Size of the follicle ovulated to GnRH on d 0 was similar ( P >0.05) for Angus (13.9 mm) and Brangus (14.1 mm) cows. However, cows on DOC 6 and 14 ovulated smaller ( P <0.05) follicles to GnRH compared to cows on DOC 10 or 18.

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Luteal regression following PGF was similar ( P >0.05) for both Angus (92.0%; 23/25) and Brangus (92.0%; 23/25) cows. Luteolysis was 100% for cows DOC 10, 14, and 18, but was lower ( P <0.05) for cows DOC 2 and 6 (both 80%). Ovulation rate following PGF was similar ( P >0.05) for Angus (88.0%; 22/25) and Brangus (92.0%; 23/25). Ovulation rate following PGF tended ( P =0.12) to be different between DOC groups with ovulation rates of 70.0, 90.0, 90.0, 100.0, and 100.0% for cows DOC 2, 6, 10, 14, and 18, respectively. Ovulatory follicle size following PGF was similar ( P >0.05) for Angus (15.0 0.6 mm) and Brangus (15.3 0.6 mm) cows. However, DOC tended ( P =0.06) to effect ovulatory follicle size following PGF Ovulatory follicle size following PGF was similar ( P >0.05) for DOC 2 (13.6 0.9 mm), 6 (14.1 0.8 mm), 10 (15.0 0.8 mm), and 14 (15.4 0.8 mm). Ovulatory follicle size was greater ( P <0.05) for DOC 18 (16.9 0.8 mm) compared to DOC 2 and 4, but was similar ( P >0.05) to DOC 10 and 14. Estrous response was greater ( P <0.05) for cows that ovulated to GnRH on d 0 (48.7%; 19/39) compared to cows that failed to ovulate to GnRH on d 0 (20.0%; 7/35). Estrous response was greater ( P =0.05) for Brangus compared to Angus cows (Table 4). Estrous response was different ( P <0.05) for DOC groups. Interval from PGF to the onset of estrus was similar ( P >0.05) for Angus and Brangus cows, but tended ( P =0.11) to be different for DOC groups. Duration of estrus tended ( P=0.12) to be greater for Brangus cows (11 h 15 m) compared to Angus cows (8 h 46 m). Duration of estrus was similar ( P >0.05) for DOC groups. Brangus cows received a greater ( P<0.05) number of mounts during estrus (53.9) compared to Angus cows (20.3). Number of mounts received during estrus was similar ( P >0.05) for DOC groups. Cows that ovulated to GnRH on d 0 (47.4%; 9/19) had similar ( P >0.05) conception rates compared to cows that failed to ovulate to GnRH on d 0 (57.1%; 4/7). Conception rates were similar ( P >0.05) for Angus compared to Brangus cows (Table 5). Conception rate was effected ( P <0.05) by DOC. Timed-AI pregnancy rates were similar ( P >0.05) for Angus and Brangus cows. Timed-AI pregnancy rate was effected ( P <0.05) by DOC. Cows that failed to ovulate to GnRH on d 0 (42.9%; 12/28) tended ( P =0.09) to have a greater timed-AI pregnancy rate compared to cows that ovulated to GnRH on d 0 (20.0; 4/20). Synchronized pregnancy rate was similar ( P >0.05) for Angus and Brangus cows. Cows 2, 6, and 18 DOC had similar ( P >0.05) synchronized pregnancy rates, but were lower ( P <0.05) compared to cows 10 and 14 DOC. However, cows 10, 14, and 18 DOC were similar ( P >0.05) to each other. Synchronized pregnancy rates were similar ( P>0.05) for cows that ovulated to GnRH on d 0 (33.3%; 13/39) and cows that failed to ovulate to GnRH on d 0 (45.7%; 16/35). In conclusion, DOC when a Select Synch/CIDR + timed-AI synchronization protocol is initiated affected ovulation rates to GnRH and ovulatory follicle size to GnRH on d 0. Cows that ovulated to GnRH on d 0 and cows that failed to ovulate to GnRH on d 0 had similar synchronized pregnancy rates. Estrous response, conception rate, timed-AI pregnancy rate, and synchronized pregnancy rate were influenced by DOC. 1 Regina Esterman Graduate Student; Brad Austin G raduate S tudent; Steaven Woodall, Former Graduate Student; Erin McKinniss Graduate Student; Joel Yelich ; Associate Professor, UF IFA, Department of Animal Sciences, Gainesville, FL

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Table 1 Effect of breed and ovulation status to GnRH on d 0 (OVGnRH) on estrous characteristics following PGF 2 in anestrous Angus and Brangus cows synchronized with a Select Synch + CIDR and timed AI synchroniz ation protocol. a Variable n Estrous response, % b Interval from PGF 2 to onset of estrus (hr, min) c Duration of estrus (hr, min) d Total mounts during estrus e A ngus 12 16.7 (12) 49 h 5 m 3 h 44 m 16 h 20 m 3 h 53 m 32 7.6 Brangus 12 41.7 (12) 49 h 6 m 2 h 21 m 5 h 21 m 2 h 27 m 30 4.8 OV to GnRH 12 41.7 (12) 51 h 16 m 1 h 30 m 6 h 8 m 3 h 1 m 34.2 3.8 No OV to GnRH 12 16.7 (12) 43 h 40 m 2 h 22 m 14 h 20 m 4 h 46 m 21.5 6.0 P values Breed P = 0.17 P > 0.05 P = 0.06 P > 0.05 OVGnRH P = 0.17 P = 0.04 P > 0.05 P = 0.13 Breed OVGnRH P > 0.05 P > 0.05 P = 0.04 P > 0.05 a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF 2 administered at the time of CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to 12 h later. Cows which had not displayed estrus were timed AI at 76 to 80 h and given GnRH. b Percentage of cows displaying estrus 3 d after PGF 2 of the total treated. c Time from PGF 2 administration to the first mount of estrus, as determined by HeatWatch d Time from the first mount of estrus to the last mount of estrus, as determined by HeatWatch e Total mounting events which occurred during estrus, as determined by HeatWatch

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Table 2 Effect of breed and ovulation status to GnRH on d 0 (OVGnRH) on estrous response, conception, timed AI pregnancy, and synchronized pregnancy rates follo wing PGF 2 in anestrous Angus and Brangus cows synchronized with a Select Synch + CIDR and timed AI synchronization protocol. a Variable n Estrous response, % b Conception rate, % c Timed AI pregnancy rate, % d Synchronized pregnancy rate, % e Angus 12 16.7 (12) 50.0 (12) 30.0 (10) 33.3 (12) OV to GnRH 6 16.7 (6) 100.0 (1) 0.0 (5) 16.7 (6) No OV to GnRH 6 16.7 (6) 0.0 (1) 60.0 (5) 50.0 (6) Brangus 12 41.7 (12) 40.0 (5) 42.9 (7) 41.7 (12) OV to GnRH 6 66.7 (6) 50.0 (4) 50.0 (2) 50.0 (6) No OV to GnRH 6 16.7 (6) 0.0 (1) 40.0 (5) 33.3 (6) P values Breed P = 0.17 P > 0.05 P > 0.05 P > 0.05 OVGnRH P = 0.17 P = 0.09 P = 0.11 P > 0.05 Breed OVGnRH P > 0.05 P > 0.05 P = 0.06 P = 0.19 a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF 2 administered at the time of CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to 12 h later. Cows which had not displayed estrus were timed AI at 76 to 8 0 h and given GnRH. b Percentage of cows displaying estrus 3 d after PGF 2 of total treated. c Percentage of cows pregnant to AI of the total that exhibited estrus and were AI. d Percentage of cows pregnant to timed AI of the total that were timed AI. e Percentage of cows pregnant during the synchronized breeding of the total treated.

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Table 3. Effect of breed and day of estrous cycle on o vulation rates to GnRH and ovulatory follicle size (LS mean SE) in estrous cycling Angus and Brangus cows synchronized with a Select Synch + CIDR and timed AI synchronization protocol. a Variable n Follicles ovulating to GnRH, % b Ovulatory follicle size, mm, (range) c Angus 25 56.0 (25) 13.9 0.6 (11 to 17) Brangus 25 52.0 (25) 14.1 0.6 (10 to 18) d 2 10 0.0 (10) d 6 10 100.0 (10) 13.2 0.6 (11 to 17) d d 10 10 30.0 (10) 15.7 1.0 (14 to 17) e d 14 10 70.0 (10) 12.7 0.7 (10 to 14) d d 18 10 70.0 (10) 15.6 0.7 (14 to 18) e P values Breed P > 0.05 P > 0.05 DOC P < 0.05 P < 0.05 a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF 2 administered at the time of CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to 12 h later. Cows which had not displayed estrus were timed AI at 76 to 80 h and given GnRH. b Percentage of cows that ovulated to GnRH on d 11 divided by the total treated. c Size of the largest follicle on d 0 that ovulated by 48 h later. d,e Means without a common superscript within a column differ (P<0.05).

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Table 4 Effect of breed and day of estrous cycle on e strous characteristics as determined by HeatWatch of estrous cycling Angus and Brangus cows synchronized with a Select Synch + CIDR and timed AI synchronization protocol. a With the exception of estrous respon se estrous characteristics are presented as LS means SE. a Variable n Estrous response, % b Interval from PGF 2 to onset of estrus (hr, min) c Duration of estrus (hr, min) d Total mounts during estrus e Angus 25 28.0 (25) 49 h 2 m 3 h 39 m 8 h 46 m 1 h 14 m 20.3 10.4 Brangus 25 48.0 (25) 54 h 26 m 2 h 47 m 11 h 15 m 57 m 53.9 8.0 d 2 10 0.0 (10) f . d 6 10 10.0 (10) g 64 h 24 m 8 h 48 m f,g 12 h 15 m 3 h 28 m 30.0 31.8 d 10 10 30.0 (10) g,h 62 h 20 m 5 h 5 m f 11 h 38 m 2 h 0 m 61.7 18.3 d 14 10 60.0 (10) h,i 50 h 2 m 3 h 35 m f,g 11 h 18 m 1 h 25 m 49.7 13.0 d 18 10 90.0 (10) i 49 h 26 m 2 h 56 m g 9 h 3 m 1 h 9 m 30.7 10.6 P values Breed P = 0.05 P > 0.05 P = 0.12 P < 0.05 DOC P < 0.01 P = 0.11 P > 0.05 P > 0.05 a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF 2 administered at the time of CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to 12 h later. Cows which had not displayed estrus were timed AI at 76 to 80 h and given GnRH. b Percentage of cows displaying estrus 3 d after PGF 2 of the total treated. c Time from PGF 2 administration to the first mount of estrus, as determined by HeatWatch d Time from the first mount of estrus to the last mount of estrus, as determined by HeatWatch e Total mounting events which occurred during estrus, as determined by HeatWatch f,g,h,i Means without a common superscript within a column differ (P<0.05).

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Table 5 Effect of breed and day of estrous cycle on estrous response and pregnancy rates in cycling Angus and Brangus cows synchronized with a Select Synch + CIDR and timed AI synchronization protocol. a Variable n Estrous response, % b Conception rate, % c Timed AI pregnancy rate, % d Synchronized pregnancy rate, % e Angus 25 28.0 (25) 57.1 (7) 38.9 (18) 44.0 (25) Brangus 25 48.0 (25) 50.0 (12) 23.1 (13) 36.0 (25) d 2 10 0.0 (10) 0.0 (0) 10.0 (10) 10.0 (10) f d 6 10 10.0 (10) 100.0 (1) 11.1 (9) 20.0 (10) f d 10 10 30.0 (10) 100.0 (3) 57.1 (7) 70.0 (10) g d 14 10 60.0 (10) 33.3 (6) 100.0 (4) 60.0 (10) g d 18 10 90.0 (10) 44.4 (9) 0.0 (1) 40.0 (10) f,g P values Breed P = 0.14 P > 0.05 P > 0.05 P > 0.05 DOC P < 0.05 P < 0.05 P < 0.05 P < 0.05 a All cows received GnRH at initiation of the 7 d CIDR treatment, with PGF 2 administered at the time of CIDR removal. Estrus was detected for 3 d, and cows that exhibited estrus were AI approximately 8 to 12 h later. Cows which had not displayed estrus were timed AI at 76 to 80 h and given GnRH. b Percentage of cows displaying estrus 3 d after PGF 2 of total treated. c Percentage of cows pregnant to AI of the total that exhibited estrus and were AI. d Percentage of cows pregnant to timed AI of the total that were timed AI. e Percentage of cows pregnant during the synchronize d breeding of the total treated. f,g Means without a common superscript within a column differ (P<0.05).