Fertility in Cebú × brown Swiss cows treated with prostaglandins, progesterone and eCG

Resumen

Objective: To evaluate the application of one or two doses of prostaglandin F2?
(PGF2?), the application of a progestogen on different days of the estrous cycle and the
usage of eCG in the estrus synchronization and fertility of Zebu × Brown Swiss cows.
Design / methodology / approach: The study was based on three protocols. The first
consisted of two treatments: PGI) 26 cows were injected with a single 25 mg dose of
PGF2? and 10 cows with two 25 mg doses of PGF2? at a 14-day interval. Protocol 2
consisted of two treatments: NG14) 11 cows were implanted with 3 mg of Norgestomet
on day 7 of their estrous cycle and NG7) 11 animals received the same dose on day 14.
In protocol 3 all cows were implanted with 3 mg of Norgestomet for 9 days, 48 h before
removing the implant, 25 mg of PGF2? was applied. Once the implants were removed,
they were distributed into two treatments. Norgestomet (n = 11) without eCG and
Norgestomet + eCG (500 IU) (n = 11).

Results: The application of PGF2? at two times had no influence (p > 0.05) in the
estrous percentages and conception. The NG7 achieved estrous synchronization in 81.8
% of the cows, in between 24 and 36 h, compared to 45.4 % of the NG14; however, the
conception rate was lower (p ? 0.05). The eCG application synchronized 90.9 % of
estrous between 24 and 36 h, compared with 36.4 % of the group with no eCG
application.
Study limitations / implications: Transrectal ultrasounds are required to assess the
ovarian structures present at the time of the estrus onset in a synchronization protocol.
Findings / conclusions: Cows that present corpus luteum do not require more than
one injection of PGF2?, the pregnancy percentage increases when Norgestomet is
implanted on day 14 of the estrous cycle, in addition the application of eCG increases
the synchronization percentage of the heat between 24 to 36 h after the progestogen
withdrawal.