Abstract
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(2 alpha) 14 d apart; Presynch), and cows in estrus after the second PGF(2 alpha) received AI (EDAI; n = 1,583). Cows not inseminated by 12 to 14 d after the second PGF(2 alpha) injection were submitted to a TAI protocol (GnRH on d 0, PGF(2 alpha) on d 7, and GnRH + TAI 72 h after PGF(2 alpha)). 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(2 alpha) 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(2 alpha) 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.