Pharmacological regulation of ovarian function in dairy cows to improve reproductive performance

Dairy herds experience low pregnancy rates and high embryonic mortality. The objective was to evaluate pharmacological strategies to improve reproductive performance. Nonlactating dairy cows (n = 17) received human chorionic gonadotropin (hCG) at estrus or no treatment. Nonlactating dairy cows (n = 20 and n = 14) and dairy heifers (n = 44) received a deslorelin implant or gonadotropin releasing homone (GnRH) for induction of ovulation. Lactating dairy cows (n = 593) received a deslorelin implant or GnRH for induction of ovulation and timed artificial insemination (TAI). Lactating dairy cows (n = 831) received no treatment or GnRH on Day 5, Day 15, or both after TAI. Lactating dairy cows (n = 179) received no treatment or a deslorelin implant at Day 27 of pregnancy. Lactating dairy cows (n = 332) were assigned to the Ovsynch or Heatsynch protocols after nonpregnancy diagnosis. Lactating dairy cows (n = 1083) received different protocols for resynchronization. Lactating dairy cows (n = 624) received GnRH on Day 23 after previous AI and were assigned to different protocols for resynchronization. Administration of hCG at estrus impaired CL function. Induction of ovulation with a deslorelin implant suppressed follicular growth, and slightly improved CL function in nonlactating cows and heifers and tended to reduce late embryonic losses in lactating cows. Administration of GnRH on Days 5 and 15 after TAI did not increase pregnancy rate. A deslorelin implant administered at 27 days of pregnancy suppressed follicular growth, induce accessory corpora lutea, increased progesterone (P4) production, an reduce late embryonic mortality in cows that formed an accessory CL. Forty to 45% of the cows detected not pregnant after AI presented a CL and the stage of the estrous cycle influenced the response to different resynchronization protocols. Administration of GnRH 23 days after AI resulted in 75% of cows with a CL at nonpregnancy diagnosis and these cows obtained similar pregnancy rate after resynchronization of ovulation with either GnRH or estradiol cypionate (ECP). For cows without a CL, administration of a P4 insert for resynchronization resulted in increased pregnancy rate in cows with ovarian cysts. In summary, treatments affected ovarian function and indicated that may be possible to increase pregnancy rate and reduce embryo mortality. Resynchronization protocols assigned based on stages of the estrous cycle increased pregnancy rate.