Five-day resynchronization programs in dairy cows including presynchronization and progesterone at two stages following artificial insemination

Abstract

Two experiments were conducted to assess pregnancy outcomes after a 5-d Ovsynch-56 Resynch program [RES; GnRH injection (d 0) 5 d before and 56 h after the first of 2 PG injections on d 5 and 6, and timed artificial insemination (TAI) on d 8] with or without a 5-d progesterone-releasing intravaginal controlled internal drug release (CIDR) insert applied at d 0. In experiment 1, nonpregnant cows were enrolled on d 35 post-AI: d-35 RES-CON (n=454) or d-35 RES-CIDR (n=495). Blood was collected on d 0 for progesterone assay. Only 76.4% of enrolled cows had high (≥1 ng/mL) progesterone on d-35 nonpregnant diagnoses (NPD). Pregnancy per AI (P/AI) diagnosed by transrectal palpation at 35 and 63 d post-TAI did not differ between treatments. An interaction between treatment and progesterone status on d 35 was detected. The d-35 RES-CIDR cows with progesterone ≥1 ng/mL at treatment initiation had reduced P/AI compared with d-35 RES-CON (27.7 vs. 36.4%), whereas the opposite effect occurred for d-35 RES-CIDR cows with progesterone <1 ng/mL compared with d-35 RES-CON (39.5 vs. 31.7%). In experiment 2, cows were enrolled on d 31 post-AI (NPD): (1) d-31 PG-3-G-RES (n=208): Pre-PG on d 31, Pre-GnRH on d 34, and RES on d 41; (2) d-41 RES-CON (n=208); or (3) d-41 RES-CIDR (n=208) as in experiment 1, but starting on d 41. In a subset of cows (more than 102 per treatment), blood samples were collected for progesterone assay and ovarian structures were mapped by ultrasonography on d 31, 34, 41, 46, 48, and 55. Pregnancy was diagnosed by ultrasonography on d 31 and 78 post-TAI. The proportion of cows with progesterone ≥1 ng/mL on d 31 was 70.6%. More d-31 PG-3-G-RES cows ovulated after Pre-GnRH (60.4%) than did d-41 RES-CON (16.5%) or d-41 RES-CIDR (9.3%) cows. More d-31 PG-3-G-RES cows had luteolysis after Pre-PG on d 31 (75.1%) than did d-41 RES-CON (7.5%) and d-41 RES-CIDR (8.6%) cows. Although more d-31 PG-3-G-RES cows were inseminated earlier, P/AI did not differ among treatments for cows inseminated after estrus or by TAI. Pregnancy per AI, however, was greater in cows starting RES on d 41 when progesterone was ≥1 ng/mL compared with <1 ng/mL (44.8 vs. 31.6%), respectively. We conclude that presynchronization of estrous cycles in nonpregnant cows with PG and GnRH before a d-41 RES 5-d program does not improve P/AI. Furthermore, addition of the CIDR insert in a 5-d program decreased P/AI only when treatment was initiated in cows on d 35 post-AI and when progesterone was ≥1 ng/mL (no corpus luteum) but not when beginning treatment on d 41.

Luteal Presence and Ovarian Response at the Beginning of a Timed Artificial Insemination Protocol for Lactating Dairy Cows Affect Fertility: A Meta-Analysis

“…It has been shown in multiple individual studies that presence of a CL at G1 [8,27,28,37] had a positive effect on P/AI in TAI protocols, which is the basis for presynchronisation protocols. However, after a systematic review, there were 3 out of 28 studies [17][18][19] indicating that the presence of a CL at the beginning of TAI protocol had no effect on P/AI. Using a meta-analytical assessment, we were able to better describe the effect size of a CL at G1 on P/AI and some additional factors such as ovulation after G1 and insemination number, which modulated this effect size.…”

“…The funnel plot depicted a moderate asymmetry ( Figure 3). There were 3 studies showing a slightly negative effect of having a functional CL at G1 [17][18][19]. These studies were only considering resynchronized TAI.…”

“…While it has been shown in multiple individual studies that either the presence of a CL at G1 [8,9] or ovulation after G1 [10][11][12] have a positive effect on P/AI in TAI protocols, there is only a small number of studies evaluating both at the same time. In addition, some studies [17][18][19] indicate that the presence of a CL at the beginning of a TAI protocol had no effect on P/AI.…”