Short communication: Presynchronization for timed artificial insemination in grazing dairy cows by using progesterone for 14 days with or without prostaglandin F_(2α) at the time of progesterone withdrawal

摘要

Progesterone-containing devices can be inserted in-travaginally for 14 d to presynchronize the estrous cycle for timed artificial insemination (TAI) in beef heifers ("14-day CIDR-PG" or "Show-Me-Synch" program). The progesterone treatment is effective for presynchronization because cattle develop a persistent dominant follicle during treatment that ovulates within 3 d after progesterone removal. The subsequent estrous cycle can be effectively used for a TAI program. Some cattle will retain a functional corpus luteum (CL) for the entire 14-d treatment period and will not be synchronized effectively because the interval to ovulation depends on the lifespan of their existing CL. The objective was to test the effect of a luteolytic dose of PGF_(2α) at progesterone removal for improving synchrony of estrus after treatment and increasing conception rate to a subsequent TAI in dairy cows. Postpartum cows (n = 1,021) from 2 grazing dairy herds were assigned to 1 of 2 presynchronization programs that used a controlled internal drug releasing (CIDR) device containing progesterone: 14dCIDR (CIDR in, 14 d, CIDR out; n = 523) or 14dCIDR+PGF_(2α) (CIDR in, 14 d, CIDR out, and PGF_(2α); n = 498). Cows were body condition scored (BCS; 1 to 5, thin to fat) and tail painted at CIDR removal. Paint score (PS) was recorded after CIDR removal [PS = 0 (all paint removed, indication of estrus), PS = 3 (paint partially removed), or PS = 5 (no paint removed; indication of no estrus)]. At 19 d after CIDR removal, all cows were treated with PGF_(2α), 56 h later treated with GnRH, and then 16 h later were TAI. Treating cows with PGF_(2α) at CIDR removal increased the percentage with PS = 0 within 5 d (58.1% vs. 68.9%; 14dCIDR vs. 14dCIDR+PGFF_(2α)). We found no effect of treatment, however, on conception rate at TAI (41.1% vs. 43.6%; respectively). The TAI conception rate increased with increasing BCS and was greater for cows that had PS = 0 within 5 d after CIDR removal. In summary, treating cows with PGFF_(2α) at CIDR removal increased the percentage of cows with all tail paint removed but did not increase percentage of pregnant cows after TAI.