FERTILITY IN ZEBÚ × BROWN SWISS COWS TREATED WITH PROSTAGLANDINS, PROGESTERONE AND eCG

Abstract

Objective: To evaluate the application of 1 or 2 doses of prostaglandin F2? (PGF2?), the use of progestogen on different days of the estrous cycle, and the use of eCG in estrus and fertility synchronization of Zebu × Brown Swiss cows.

Design / Methodology / Approach: The study was based on three protocols. Protocol 1 consisted of two treatments: PGI) 26 cows were injected with a single dose of 25 mg PGF2?, and 10 cows with two doses of 25 mg PGF2? with a 14 day interval. Protocol 2 consisted of two treatments: NG14) 11 cows were implanted with 3 mg Norgestomet on day 7 of the estrous cycle, and NG7) 11 animals received the same dose on day 14. In protocol 3, all the cows were implanted with 3 mg Norgestomet for 9 days, 48 h before removing the implant, 25 mg PGF2? was applied. Once the implant was removed, the cows were distributed into two treatments. Norgestomet (n=11) without eCG and Norgestomet + eCG (500 IU) (n=11).   

Results: The application of PGF2? on two occasions had no influence (p> 0.05) on the percentages of estrus or pregnancies. NG7 achieved estrus synchronization in 81.8% of the cows between 24 and 36 h, compared with 45.4% of NG14; however, the pregnancy rate was lower (p<0.05). The application of eCG synchronized 90.9% estrus between 24 and 36 h, compared with 36.4% in the group where no eCG was applied.

Study limitations / implications: The use of transrectal ultrasound is required to evaluate the ovarian structures present at the time of initiating an estrus synchronization protocol.

Findings / conclusions: Cows that present corpus luteum do not require more than one injection of PGF2?, the percentage of pregnancy increases when Norgestomet is implanted on day 14 of the estrous cycle, in addition the application of eCG increases the percentage of synchronization of heat of the 24 to 36 h after withdrawal of progestogen