| Two experiments were conducted to assess pregnancy outcomes after a 5-d Ovsynch-56 Resynch (RES; GnRH injection 5 d before [GnRH-1; d 0] and 56 h (GnRH-2) after last PGF2&agr; [PGF] injection on d 5 and 6, TAI on d 8) with and without a progesterone-releasing intravaginal controlled internal drug release (CIDR) 5-d insert. In Exp. 1, nonpregnant cows were enrolled on d 34 post-AI: d 34 RES-CON (n = 528) or d 34 RES-CIDR (n = 503). Blood was collected for progesterone assay. Pregnancy per AI (P/AI) was diagnosed by uterine palpation per rectum at 34 and 69-d post-TAI. Only 76% of 1,023 cows had high (≥1 ng/mL) progesterone on d 34 nonpregnant diagnoses (NPD). The d 34 RES-CIDR cows with low (<1 ng/mL) progesterone at treatment initiation had greater P/AI than d 34 RES-CON (37.7 vs. 29.4%), whereas d 34 RES-CIDR cows with high progesterone had lesser P/AI than d 34 RES-CON (27.4 vs. 34.3%). In Exp. 2, cows were enrolled on d 31 post-AI (NPD): (1) d 31 PG-3-G (n = 102): Pre-PGF on d 31, Pre-GnRH on d 34, and RES on d 41 (n = 102); (2) d 41 RES-CON (n = 108) as Exp, 1. but on d 41; and (3) d 41 RES-CIDR (n = 101) as Exp. 1, but on d 41. Blood samples for progesterone assay and ovarian structures were mapped by ultrasonography on d 31, 34, 41, 46, and 48. Pregnancy was diagnosed by ultrasonography on 31 and 59 d post-TAI. Proportion of cows with high progesterone on d 31 was 70.6%. More cows ovulated after Pre-GnRH of d 31 PG-3-G (60.4%) than for d 41 RES-CON (12.5%) or d 41 RES-CIDR (17.1%). More PG-3-G cows had luteolysis after Pre-PG on d 31 than cows in other treatments (73.7 vs. < 11%). The P/AI was greater in cows starting RES on d 41 when progesterone was low (44%) than high (33%), but no treatment differences were detected at 31 d after TAI. We conclude that successful supplementation of the CIDR insert is corpus luteum or progesterone-dependent for cows initiating RES on d 34. |
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