Mature Angus and Angus × Hereford
cows were used to determine the effects of confinement
area and number of cows in estrus on estrous behavior.
During each of 2 replicates, 32 nonpregnant, nonlactating
cows were maintained in a drylot (60 × 100 m) or in
a pasture (12 ha). Estrous cycles were synchronized with
2 injections of PGF2α 10 to 14 d apart at the initiation
of the experiment. Thereafter, PGF2α was administered
between d 6 and 18 of the estrous cycle so that 1, 2 to 3,
4 to 6, or ≥7 cows were in estrus at the same time. Concentrations
of progesterone were quantified in plasma
at treatment to ensure cows had a normal response to
PGF2α. Duration of estrus and the number of mounts
received during estrus were recorded by HeatWatch. If
any part of estrus for a cow occurred at the same time
as estrus for another cow, the cow was considered to
have concurrent estrus with the other cow. Cows in the
drylot had a shorter (P < 0.02; 61.8 ± 3.1 h) interval
to estrus after PGF2α compared with cows on pasture
(72.8 ± 3.3 h). The interval to estrus was longer (P <
0.07) when cows were treated with PGF2α on d 10 to 13
(76.7 ± 3.3 h) of the estrous cycle than when treated
on d 6 to 9 (62.3 ± 4.7 h) or d 14 to 18 (62.9 ± 3.6 h).
Increasing the number of cows concurrently in estrus
increased the number of mounts each cow received per
estrus (P < 0.001) and the duration of estrus (P <
0.01). When only 1 cow was in estrus, she received 11.0
± 6.2 mounts during 11.6 ± 1.5 h. When ≥7 cows were
in estrus at the same time, each cow received 50.4 ±
3.2 mounts during 17.3 ± 0.8 h. Cows in drylot were
in estrus longer (P < 0.04; 16.4 ± 0.8 h) than cows on
pasture (14.2 ± 0.7 h). Duration of the longest interval
between mounts received decreased (P < 0.002) as the
number of cows in estrus at one time increased (5.3 ±
0.7 h for 1 estrous cow; 2.6 ± 0.3 h when ≥7 cows were
in estrus). We conclude that increasing the number of
beef cows in estrus at the same time will increase the
number of times a cow is mounted and the duration
of estrus. The increase in estrous behavior associated
with more cows in estrus could increase the number of
estrous cows detected with infrequent visual observation.
Mature Angus and Angus × Herefordcows were used to determine the effects of confinementarea and number of cows in estrus on estrous behavior.During each of 2 replicates, 32 nonpregnant, nonlactatingcows were maintained in a drylot (60 × 100 m) or ina pasture (12 ha). Estrous cycles were synchronized with2 injections of PGF2α 10 to 14 d apart at the initiationof the experiment. Thereafter, PGF2α was administeredbetween d 6 and 18 of the estrous cycle so that 1, 2 to 3,4 to 6, or ≥7 cows were in estrus at the same time. Concentrationsof progesterone were quantified in plasmaat treatment to ensure cows had a normal response toPGF2α. Duration of estrus and the number of mountsreceived during estrus were recorded by HeatWatch. Ifany part of estrus for a cow occurred at the same timeas estrus for another cow, the cow was considered tohave concurrent estrus with the other cow. Cows in thedrylot had a shorter (P < 0.02; 61.8 ± 3.1 h) intervalto estrus after PGF2α compared with cows on pasture(72.8 ± 3.3 h). The interval to estrus was longer (P <0.07) when cows were treated with PGF2α on d 10 to 13(76.7 ± 3.3 h) of the estrous cycle than when treatedon d 6 to 9 (62.3 ± 4.7 h) or d 14 to 18 (62.9 ± 3.6 h).Increasing the number of cows concurrently in estrusincreased the number of mounts each cow received perestrus (P < 0.001) and the duration of estrus (P <0.01). When only 1 cow was in estrus, she received 11.0± 6.2 mounts during 11.6 ± 1.5 h. When ≥7 cows werein estrus at the same time, each cow received 50.4 ±3.2 mounts during 17.3 ± 0.8 h. Cows in drylot werein estrus longer (P < 0.04; 16.4 ± 0.8 h) than cows onpasture (14.2 ± 0.7 h). Duration of the longest intervalbetween mounts received decreased (P < 0.002) as thenumber of cows in estrus at one time increased (5.3 ±0.7 h for 1 estrous cow; 2.6 ± 0.3 h when ≥7 cows werein estrus). We conclude that increasing the number ofbeef cows in estrus at the same time will increase thenumber of times a cow is mounted and the durationof estrus. The increase in estrous behavior associatedwith more cows in estrus could increase the number ofestrous cows detected with infrequent visual observation.
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