Addition of a second dose of prostaglandin F2α to a fixed-time AI protocol improves fertility of anestrous dairy cows and without hyperthermia

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.