Effect of gonadotropin-releasing hormone and prostaglandin F2 alpha on reproduction in postpartum dairy cows

30 dairy cows were injected intramuscularly with 10 mu g GnRH daily on days 10-16 post partum and with 25 mg PGF2 alpha 14 days after the last injection of GnRH; 29 herdmate females (controls) were treated similarly, but were injected with saline in place of GnRH and PGF2 alpha . The internal genitalia were palpated before each injection to diagnose any abnormalities, and blood was sampled immediately before each injection and 30 h after the PGF2 alpha injection or last saline injection. For the experimental and control groups, the interval from parturition to 1st detected oestrus post partum averaged 36.8 plus or minus 3.5 and 41.1 plus or minus 3.2 days resp., the interval from parturition to 1st service 60.6 plus or minus 3.1 and 63.2 plus or minus 3.9 days, the CR to 1st service 34.6 plus or minus 9.5 and 46.4 plus or minus 9.6%, number of services to conception 1.8 plus or minus 0.2 and 1.7 plus or minus 0.2, incidence of cystic ovaries 3.6 plus or minus 3.6 and 14.3 plus or minus 6.7%, incidence of abortion or resorption 4.8 plus or minus 4.8 and 8.7 plus or minus 6.0%, and culling rate 23.1 plus or minus 8.4 and 14.8 plus or minus 7.0%. It is concluded that, in the absence of abnormalities of the reproductive tract, there is no economic advantage in using a GnRH-PGF2 alpha regime post partum with dairy cattle..