Addition of a second dose of prostaglandin F2α to a fixed-time AI protocol improves fertility of anestrous dairy cows and without hyperthermia
2015
This study was conducted during January to December 2014 in two dairy farms in the Minas Gerais State - Brazil, the aim was to evaluate if addition of a second prostaglandin (PG) F2α dose improves fertility of anestrous lactating Holstein cows submitted to an estradiol/progesrterone(P4) based timed AI (TAI) protocol. Ovaries were scanned by ultrasound to determine if a corpus luteum (CL) was present at the protocol initiation (d-11) and on the day of PGF2α (d-4). Cows without CL on d-11 and d-4 were classified as anestrous (n=436). Anestrous cows were submitted to the TAI protocol: d-11: two intravaginal P4 devices (1.9g P4,CIDR, Zoetis) and 2.0 mg of estradiol benzoate (EB) i.m. (Gonadiol, Zoetis); d-4, 25mg of PGF2α i.m. (Lutalyse, Zoetis) and withdrawal of one CIDR; d- 2 withdrawal of the second CIDR and 1.0 mg i.m. of estradiol cypionate (E.C.P., Zoetis); on d0 TAI. On d-4, cows were randomly assigned to one of two treatments: one dose of PGF2α on d-4 (1PGF) or two doses of PGF2α (2PGF), the first on d -4 and the second on d-2. Rectal temperature was measured on the day of TAI and 7 days later. The average rectal temperature was calculated and the cows were divided into two groups: without hyperthermia (<39.1°C) or with hyperthermia (≥39.1°C). Pregnancy was diagnosed 60 d after AI. Binomial variables were analyzed using the GLIMMIX and continuous using the MIXED procedures of SAS. The synchronization rate in this study was 76.4% (n = 436) and the percentage of cows with hyperthermia was 58% (n = 436). The 2PGF treatment tended to improve the synchronization rate (80.2% [n=218] vs. 72.4% [n=218] P=0.07). An interaction (P=0.05) between treatment and hyperthermia was observed for pregnancy per AI (P/AI) on d 60. For hyperthermic cows, P/AI were 9.1% (n=123) and 9.4% (n=130) for 1PGF and 2PGF, respectively. For cows without hyperthermia, P/AI were 16.3% (n=95) and 30.0% (n=88) in 1PGF and 2PGF, respectively. When only ovulated cows were included in the analysis, then an interaction (P=0.05) existed between treatment and hyperthermia on P/AI at 60d. For cows with hyperthermia, P/AI were 13.8% (n=80) and 12.1% (n=100) in 1PGF and 2PGF, respectively. For cows not suffering of hyperthermia, P/AI were 19.4% (n=78) and 34.8% (n=75) in 1PGF and 2PGF, respectively. The addition of a second PGF2α dose during the TAI protocol increased fertility in anestrous dairy cows without hyperthermia on the first 7 days after AI.
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