Fertility of postpartum dairy cows after administration of gonadotropin-releasing hormone and prostaglandin F2 alpha: a field trial.

Our objective was to examine further the potential profertility effects of gonadotropin-releasing hormone and prostaglandin F2 alpha in postpartum Holstein cows. Reproductive performance was monitored in 843 cows milked thrice daily. One group of cows (n = 218) was untreated, while three groups received either 100 micrograms gonadotropin-releasing hormone administered once between d 11 and 25 (n = 211); 25 mg prostaglandin F2 alpha given once between d 11 and 25 (n = 215); or 25 mg prostaglandin F2 alpha given once between d 25 and 40 postpartum (n = 190). No profertility effects were detected in cows, regardless of their health status during the periparturient period, except cows given gonadotropin-releasing hormone between d 11 and 18 had shorter intervals to first estrus and to first service than controls. Cows with reproductive disorders (abnormal health status) in the concurrent lactation had longer intervals from calving to conception after receiving gonadotropin-releasing hormone between d 18 and 25 or prostaglandin F2 alpha between d 33 and 40. Abnormal health status adversely affected every reproductive trait measured. Early postpartum treatments with either hormone failed to improve reproductive performance of dairy cows, in contrast to several reports of profertility effects for gonadotropin-releasing hormone, and a few reports for prostaglandin F2 alpha.