Physiological predictors of ovulation and pregnancy risk in a fixed-time artificial insemination program

Abstract

The objective of this study was to determine the relative importance and contribution of several physiological factors as predictors of pregnancy risk in an Ovsynch (GnRH-1 - 7d - PGF - 56h - GnRH-2 - 16h - artificial insemination) timed artificial insemination program: (1) age of the corpus luteum (CL; original CL, new CL, or both in response to GnRH-1) and resulting progesterone concentrations as they affected luteolysis, ovulation after GnRH-2, and pregnancy risk; (2) progesterone concentration before GnRH-1 and GnRH-2 on subsequent ovulatory response to GnRH-1 and GnRH-2 as well as pregnancy risk; and (3) a combination of these factors in a multivariable logistic regression model to predict pregnancy risk. Original data from 7 published studies were combined including ovulatory responses to both GnRH injections, blood progesterone concentrations before GnRH-1, before PGF, and at 48h after PGF, pregnancy per artificial insemination at d 32 and 60 after artificial insemination, and intervening pregnancy loss. Ovulation outcomes were greater at lesser progesterone concentrations after both GnRH injections despite the fact that pregnancy outcomes were greatest when progesterone exceeded 3ng/mL before GnRH-1 and PGF, suggesting that greater progesterone concentration before GnRH-1 and incidence of ovulation act via different mechanisms to improve subsequent fertility. Ovulation after GnRH-2 and subsequent pregnancy outcome were positively related to lesser concentrations of progesterone at 48h after PGF; however, for maximal pregnancy outcome, progesterone should be <0.5ng/mL. Cows with a CL that also formed a new CL after GnRH-1 had the greatest pregnancy outcome, whereas cows with only a new CL (i.e., anovulatory cows and those at or near estrus without a CL at GnRH-1) had the poorest pregnancy outcome. Pregnancy loss was not affected by CL status during the timed artificial insemination program. Receiver operator curves produced cut points of progesterone concentration that predicted ovulation and pregnancy risk. Selected cut points of progesterone concentration 48h after PGF produced true positive risks greater than 90% and false positive risks less than 25%, thus demonstrating the high predictability of ovulation after GnRH-2 and subsequent pregnancy outcome based on progesterone concentration. We conclude that progesterone concentration is highly predictive of ovulation and pregnancy risk in addition to body condition, size of ovulatory follicle, and parity.

Dose frequency of prostaglandin F2α administration to dairy cows exposed to presynchronization and either 5- or 7-day Ovsynch program durations: Ovulatory and luteolytic risks

“…That more cows with both older and new CL had more complete luteolysis than cows with only a new, younger CL is consistent with our previous report (Stevenson, 2016). Earlier luteolysis of new CL is also consistent with the report that human chorionic gonadotropin (hCG)-induced luteal structures or CL on d 10 of the estrous cycle were responsive to PGF 2α when the new CL or hCG-induced luteal structures were less than 5 d old when they were in the presence of an older CL (Howard and Britt, 1990).…”

“…Progesterone profiles differed between cows with a mature CL and those with a new plus mature CL at the time PGF 2α was administered, as we observed in an earlier report of combined studies consisting of 2,104 cows (Stevenson, 2016). Although no differences were detected in pregnancy risk between those latter 2 groups of cows in the present study (Table 5), with sufficient observations in the latter publication, pregnancy risk was greater in cows having ovulated in response to GnRH-1 (mature CL plus new CL; 42.4%) compared with cows having only a mature CL (37.0%).…”

“…This improvement in pregnancy risk coupled with a small increase in the concentration of progesterone (6.0 ng/mL) in the former compared with the latter group (5.3 ng/mL) before the administration of PGF 2α as observed in the present study (5.8 vs. 5.0 ng/mL; Table 5) was associated with positive benefits of the elevated progesterone environment for the growth of the preovulatory follicle or oocyte, uterine function, or both. Pregnancy risk was the least in cows bearing only a new CL in the present study (26.1%) and in Stevenson (2016;31.1%) in addition to having lesser progesterone concentration at PGF 2α . Taken together, small to significant increases in progesterone concentration and likely improved synchronization of the developing preovulatory follicle and its oocyte seemed to facilitate the greater pregnancy risk in Stevenson (2016), as observed in the present study (Table 5) for cows having both the new CL plus more mature CL compared with cows having only a mature luteal structure or only a new CL.…”

“…In combined studies (Stevenson, 2016) consisting of 2,104 cows, more than 78% of the variation in pregnancy per AI (P/AI) after a timed AI program was explained (multiple regression modeling) by (1) ovulation success after GnRH-2, (2) concentrations of progesterone >0.5 ng/mL before PGF 2α , and (3) concentrations of progesterone <0.5 ng/mL by 48 h after PGF 2α reflecting complete luteolysis. Other factors of lesser importance in that model were BCS, size of the ovulatory follicle before GnRH-2, and parity.…”

Increasing estrus expression in the lactating dairy cow

“…Cows beginning an ovulation-synchronization program with greater progesterone concentrations had more pregnancies per AI (P/AI) compared with cows beginning the program with lesser progesterone concentrations (Bisinotto et al, 2010;Stevenson, 2016). Furthermore, cows ovulating a follicle from the second follicular wave of the estrous cycle during elevated concentrations of progesterone had greater P/AI than cows ovulating a first follicular wave follicle (low progesterone; Bisinotto et al, 2010).…”