Efficacy of gonadotropin-releasing hormone administered at the time of artificial insemination of heifers and postpartum and repeat breeder dairy cows.

The efficacy of gonadotropin releasing hormone (GnRH) on the fertility of dairy heifers and postpartum cows was studied. In one study, 300 cows were assigned randomly to 1 treatment from a 2 X 2 design, and 2 ml of 0.15M saline solution or 100 micrograms of GnRH was given IM on postpartum day (PPD) 14 and at the time of 1st postpartum breeding. In a 2nd study, repeat breeder cows (n = 346) were given saline solution or GnRH at the time of the 3rd breeding. In a 3rd study, heifers (n = 185) were given saline solution or GnRH at 1st breeding. Animals were observed for repeat estrus, and pregnancy diagnoses were made by rectal palpation 45 to 60 days after breeding. Conception rates were 15% to 18% higher for cows given GnRH, whether at PPD 14 or at the first postpartum breeding. When GnRH was given at the first breeding, conception rates were significantly higher (P less than 0.05). Conception rates for repeat breeder cows given GnRH were 25% higher than those in controls (P less than 0.005). Conception rates for heifers did not differ between treatments.