Comparison of Different Prostaglandin F2α Treatments in the GnRH ...

the ground under pasture conditions. On
the last day of MGA feeding (day 7 of the
experiment), cows were randomly
assigned to one of three treatments within
each location to receive either 5 cc of
PGF 2α (Lutalyse Sterile Solution ® ), 2 cc
of cloprostenol sodium (Estrumate ® ), or
2.5 cc of PGF 2α (Split-Lutalyse Sterile
Solution ® ) on days 7 and 8. Cows were
timed-AI and received 2 cc of GnRH
approximately 72 to 80 h after the last
MGA feeding.
Cows were exposed to bulls
approximately 10 d following timed-AI
for a breeding season of approximately 60
d at all locations. Pregnancy status was
determined between 52 and 56 d after the
timed AI using a real-time B-mode
ultrasound. The data presented in this
paper includes timed-AI pregnancy
(number of animals pregnant to the timed-
AI divided by the number treated) and 30-
d pregnancy rates (number of cows
pregnant during the first 30 d of the
breeding season divided by the number
treated).
Results
There was no statistical difference in
the timed-AI pregnancy rates between
PGF 2α treatments (Figure 2). Although,
5% more Estrumate ® treated cows and 3%
more Split-Lutalyse ® cows became
pregnant compared to the single Lutalyse ®
treatment. For the Estrumate ® treatment,
this calculated to 15 extra pregnancies. A
greater number of calves born in the
subsequent calving season could certainly
have a positive economic benefit to a
producer. Furthermore, the Estrumate ®
treatment does not require the additional
cattle handling required by the Split-
Lutalyse ® treatment. Additional research
will need to be conducted with an
increased number of cattle and in
postpartum lactating cows of Bos indicus
breeding to determine if these results can
be replicated.
The importance of body condition on
reproductive function and breeding season
pregnancy rates has been well
documented by scientists and beef
producers. Body condition score can also
influence the effectiveness of
synchronization protocols. In the present
experiment, cows with a body condition
score ≥5 had a 6% increase in timed-AI
pregnancy rates (Figure 3) compared to
cows with a body condition score