Supplementation of progesterone via controlled internal drug release inserts during ovulation synchronization protocols in lactating dairy cows

摘要

Our objective was to determine the effect of exogenous progesterone (P4) during a timed artificial insemination (TAI) protocol on pregnancies per AI (P/ AI) in dairy cows not previously detected in estrus. Lactating cows (n = 3,248) from 7 commercial dairy herds were submitted to a presynchronization protocol (2 injections of PGF_(2α) 14 d apart; Presynch), and cows in estrus after the second PGF_(2α) received AI (EDAI; n = 1,583). Cows not inseminated by 12 to 14 d after the second PGF_(2α) injection were submitted to a TAI protocol (GnRH on d 0, PGF_(2α) on d 7, and GnRH + TAI 72 h after PGF_(2α)). At onset of the TAI protocol, cows were balanced by parity and days in milk and assigned randomly to receive no exogenous P4 (control, n = 803) or a controlled internal drug release (CIDR) insert containing 1.38 g of P4 from d 0 to 7 (CIDR, n = 862). Blood samples were collected at the second PGF_(2α) injection of the Presynch and on the day of the first GnRH injection of the TAI protocol for P4 determination. When P4 in both samples was <1 ng/mL, cows were classified as anovular, whereas cows having at least 1 sample ≥1 ng/mL were classified as cyclic. Concentration of P4 at 11 to 14 d after AI was determined in a subgroup of cows (n = 453) from 2 herds. Pregnancy was diagnosed at 40 ± 5 and 65 ± 5 d after AI. Proportion of cows inseminated on estrus after the second PGF_(2α) injection of the Presynch protocol differed among herds (range = 26.7 to 59.8%). Overall P/ AI for EDAI cows at 40 ± 5 and 65 ± 5 d were 36.2 and 33.7%, respectively, and pregnancy loss was 8.8%. Proportion of cyclic cows at the onset of the TAI protocol differed among herds (range from 66.5 to 86.3%), but did not differ between treatments (control = 72.4%, CIDR = 74.1%). Treatment affected P/AI at 40 ± 5 (control = 33.3%, CIDR = 38.1%) and 65 ± 5 (control = 30.0%, CIDR = 35.1%) d after AI but did not affect pregnancy loss (8.6%). Cyclic cows had greater P/AI at 40 ± 5 (38.2 vs. 29.3%) and 65 ± 5 d (35.1 vs. 26.1%) after AI, but cyclic status had no effect on pregnancy loss. Treatment affected P4 concentration after AI, with more CIDR cows having P4 ≥1 ng/mL (94.4 vs. 86.9%) and P4 ≥3.2 ng/mL (81.8 vs. 68.0%) at 11 to 14 d after AI compared with control cows. Treatment of cows not previously detected in estrus with a CIDR insert during a TAI protocol increased proportion of cows with functional CL after AI and P/AI.