Effect of GnRH and PGF₂ alpha on Reproduction in Postpartum Dairy Cows

Abstract

Thirty dairy cows were injected intramuscularly with 100 mcg gonadotropin releasing hormone ( GnRH) at 10-16 days postpartum followed by 25 mg. prostaglandin F2 alpha (PGF2 alpha) 14 days later. Twenty-nine other dairy cows (controls) were treated in a similar manner but saline was injected rather than GnRH or PGF2 alpha. Blood samples were taken for progresterone analysis before each injection and approximately 30 hours after the PGF2 alpha or second saline injection. The reproductive tract was evaluated by rectal palpation at the time of each injection. Only cows without obvious uterine infection were used and any pathological conditions that developed subsequently were treated after the experimental period. The cows were inseminated at the first estrus after 135-40 days postpartum.