Five-day Resynch Programs in Dairy Cows Including Controlled Internal Drug Release at Two Stages Post-Artificial Insemination

Two experiments were conducted to assess pregnancy outcomes after a 5-day Ovsynch-56 Resynch (RES; gonadotropin-releasing hormone injection 5 days before [GnRH-1; d 0] and 56 hours (GnRH-2) after PGF2α [PG] injections on day 5 and 6, timed artificial insemination [TAI] on day 8) with and without a progesterone-releasing intravaginal controlled internal drug release (CIDR) 5-day insert. In Exp. 1, nonpregnant cows were enrolled on day 34 postAI: day 34 RES-CON (n = 528) or day 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 62 days post-TAI. Only 76% of 1,031 cows had high progesterone (≥1 ng/mL) on day 34 at the nonpregnant diagnosis. No differences in P/AI were detected between treatments. The day-34 RES-CIDR cows with low (<1 ng/mL) progesterone, however, had greater (P = 0.036) P/AI than day-34 RES-CON cows (37.7 vs. 29.4%), whereas day-34 RES-CIDR cows with high progesterone had lesser P/AI than day-34 RES-CON (27.4 vs. 34.3%). In Exp. 2, cows were enrolled on day 31 post-AI after a nonpregnant diagnosis: (1) day 31 PG-3-G (n = 102): Pre-PG on day 31, Pre-GnRH on day 34, and RES on day 41 (n = 102); (2) day 41 RES-CON (n = 108) as Exp. 1, but on day 41; and (3) day 41 RES-CIDR (n = 101) as Exp. 2, but on day 41. Blood was collected for progesterone assay and ovarian structures were mapped by ultrasonography on days 31, 34, 41, 46, and 48. Pregnancy was diagnosed by ultrasonography on days 31 and 59 post-TAI. The proportion of cows with high progesterone on day 31 was 70.6%. More (P < 0.001) cows ovulated after Pre-GnRH on day 31 PG-3-G (60.4%) than for day 41 RES-CON (12.5%) or day 41 RES-CIDR (17.1%). More (P < 0.001) PG-3-G cows had luteolysis after Pre-PG on day 31 than other treatments (73.7 vs. < 11%). The proportion of cows with high progesterone on day 41 at GnRH-1 tended (P = 0.10) to be greater for PG-3-G (75.6%) than for other treatments (65 to 70%). The P/AI was greater in cows starting RES on day 41 when progesterone was low (44%) than when it was high (33%), but no treatment differences were detected 31 days after TAI (PG-3-G = 33.3%; d 41 RES-CON = 38.9%; d 41 RES-CIDR = 35.6%). We concluded that improved P/AI for cows initiating the 5-day RES on day 34 without a corpus luteum is progesterone-dependent because addition of the CIDR insert to the RES treatment improved P/AI in cows with low progesterone (Exp. 1). Although day-31 PG-3-G increased luteolysis and produced greater ovulation rates before the onset of RES, no increase in P/AI was detected compared with RES started on day 41 with or without a CIDR insert.

Five-day Resynch Programs in Dairy Cows Including Controlled Internal Drug Release at Two Stages Post-Artificial Insemination S. L. Pulley, S. L. Hill, and J. S. Stevenson Summary Two experiments were conducted to assess pregnancy outcomes after a 5-day Ovsynch-56 Resynch (RES; gonadotropin-releasing hormone injection 5 days before [GnRH-1; d 0] and 56 hours (GnRH-2) after PGF 2α [PG] injections on day 5 and 6, timed artificial insemination [TAI] on day 8) with and without a progesterone-releasing intravaginal controlled internal drug release (CIDR) 5-day insert. In Exp. 1, nonpregnant cows were enrolled on day 34 post-AI: day 34 RES-CON (n = 528) or day 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 62 days post-TAI. Only 76% of 1,031 cows had high progesterone (≥1 ng/mL) on day 34 at the nonpregnant diagnosis. No differences in P/AI were detected between treatments. The day-34 RES-CIDR cows with low (<1 ng/mL) progesterone, however, had greater (P = 0.036) P/AI than day-34 RES-CON cows (37.7 vs. 29.4%), whereas day-34 RES-CIDR cows with high progesterone had lesser P/AI than day-34 RES- CON (27.4 vs. 34.3%). In Exp. 2, cows were enrolled on day 31 post-AI after a nonpregnant diagnosis: (1) day 31 PG-3-G (n = 102): Pre-PG on day 31, Pre-GnRH on day 34, and RES on day 41 (n = 102); (2) day 41 RES-CON (n = 108) as Exp. 1, but on day 41; and (3) day 41 RES-CIDR (n = 101) as Exp. 2, but on day 41. Blood was collected for progesterone assay and ovarian structures were mapped by ultrasonography on days 31, 34, 41, 46, and 48. Pregnancy was diagnosed by ultrasonography on days 31 and 59 post-TAI. The proportion of cows with high progesterone on day 31 was 70.6%. More (P < 0.001) cows ovulated after Pre-GnRH on day 31 PG-3-G (60.4%) than for day 41 RES-CON (12.5%) or day 41 RES-CIDR (17.1%). More (P < 0.001) PG-3-G cows had luteolysis after Pre-PG on day 31 than other treatments (73.7 vs. < 11%). The proportion of cows with high progesterone on day 41 at GnRH-1 tended (P = 0.10) to be greater for PG-3-G (75.6%) than for other treatments (65 to 70%). The P/AI was greater in cows starting RES on day 41 when progesterone was low (44%) than when it was high (33%), but no treatment differences were detected 31 days after TAI (PG-3-G = 33.3%; d 41 RES-CON = 38.9%; d 41 RES-CIDR = 35.6%). We concluded that improved P/AI for cows initiating the 5-day RES on day 34 without a corpus luteum is progesterone-dependent because addition of the CIDR insert to the RES treatment improved P/AI in cows with low progesterone (Exp. 1). Although day-31 PG-3-G increased luteolysis and produced greater ovulation rates before the onset of RES, no increase in P/AI was detected compared with RES started on day 41 with or without a CIDR insert.

Introduction
Lactating dairy cows generally have poorer pregnancy outcomes at second and subsequent services when timed artificial insemination (TAI) programs are applied. Currently, many well-managed dairies are achieving TAI pregnancies in the 40% range at first service after calving. Pregnancy outcomes for TAI repeat services are in the 30 to 35% range for the most part.
Poorer pregnancy outcomes of repeat or Resynch (RES) inseminations seem to be associated with poorer ovulatory responses to gonadotropin-releasing hormone (GnRH) and failure of the corpus luteum to regress in response to PGF 2α (PG). Studies in which open cows are pretreated with GnRH or human chorionic gonadotropin (hCG) 7 days before RES have improved pregnancy outcomes, but they also extend the inter-insemination interval for individual cows because of the delay between open diagnosis and re-insemination. Injecting PG 7 or 11 days before RES also delays reinsemination, but when coupled with detection of estrus, more cows are reinseminated before the follow-up RES is applied to those cows not inseminated.
Our objective was to determine the value of applying progesterone in the form of a CIDR insert to cows diagnosed open at day 34 after last insemination (Exp. 1). A second experiment was performed with the same objective. The RES program with or without the CIDR insert, however, was applied on day 41, and a third treatment included a presynchronization (PG + GnRH) treatment before RES. In both experiments, a 5-day RES-Ovsynch protocol was used.

Experimental Procedures
Lactating dairy cows from two herds in northeast Kansas were enrolled in the study. All cows were milked three times daily and fed diets consisting of alfalfa hay, corn silage, soybean meal, whole cottonseed, corn or milo grain, corn gluten feed, vitamins, and minerals. Non-pregnant cows were assigned randomly to either day-31 PG-3-G (Pre-PG on day 31, Pre-GnRH on day 34, and RES on day 41; n = 102), day-41 RES-CON (same as in Exp. 1, but on day 41; n = 108) or day-41 RES-CIDR (as Exp. 2 but on day 41, n =101, Figure 2). Ovarian structures were recorded and mapped by ultrasonography on days 31, 41, 46, and 48 to determine the incidence of luteolysis, ovulation, and double ovulation in all cows. Cows returning to estrus before TAI were inseminated and designated as early bred (EB).
Pregnancy per AI (P/AI) was diagnosed at 34 days and confirmed at 62 days post-TAI by uterine palpation per rectum by a single veterinarian (Exp. 1) or at 31 days and confirmed 59 days post-TAI by ultrasonography (Exp. 2).
Blood was sampled from all cows by puncture of the coccygeal vein or artery into evacuated tubes at nonpregnant diagnosis. Blood samples were collected to determine progesterone concentrations at either day 34 (Exp. 1) or at days 31, 34, 46, and 48 (Exp. 2). Samples were immediately cooled and stored at 5°C for 16 hours. Blood tubes were centrifuged at 1,000 x g for 15 minutes in a refrigerated centrifuge at 5°C for serum separation and harvest. Serum samples were frozen and stored at -20°C until assayed for progesterone by radioimmunoassay.
It seems clear from this experiment that no benefit to pregnancy outcome is accrued from using CIDR in a Resynch application for cows with elevated progesterone (functional corpus luteum; 76% of cows treated) at the onset of a 5-day Resynch program for cows that are between days 34 and 40 since last insemination. Increased P/AI was observed in cows treated with the CIDR insert only when they had low progesterone (no corpus luteum; 24% of cows treated) at the onset of RES.

Experiment 2
The proportion of cows with high progesterone on day 31 was 70.6%. More (P < 0.001) cows ovulated after Pre-GnRH of day-31 PG-3-G than for day-41 RES-CON or day-41 RES-CIDR (Table 1). More (P < 0.001) PG-3-G cows had luteolysis after Pre-PG on day 31 than other treatments (Table 1). The proportion of cows with high progesterone on day 41 at GnRH-1 tended (P = 0.10) to be greater for PG-3-G than for other treatments ( Table 1). The P/AI was greater in cows starting RES on day 41 when progesterone was low (44%) than when it was high (33%), but no overall treatment differences in P/AI were detected 32 days after TAI (PG-3-G = 33.3%; day-41 RES-CON = 38.9%; day-41 RES-CIDR = 35.6%; Figure 4).
Some have reported improved P/AI in RES cows in which the RES protocol was delayed after open diagnosis and cows were pretreated with PG before initiating the RES protocol. Most of the advantage of using PG is accrued by inseminating those cows that are detected in estrus and enrolling only those not yet inseminated in the follow-up RES protocol. Therefore, although no P/AI advantage occurred after pretreating open cows with PG, the major benefit accrued when detection of estrus was included as part of the program before applying the RES protocol to cows not inseminated.
We concluded that improved P/AI occurred only when applying the CIDR insert to cows with low progesterone when initiating the 5-day RES on d 34 (Exp. 1). Although d 31 PG-3-G increased rates of luteolysis and ovulation before RES, no increase in P/AI was detected compared with the 5-day RES started on d 41 with or without a CIDR insert (Exp. 2).