Effect of progesterone and/or estradiol treatments prior to induction of ovulation on subsequent luteal lifespan in anestrous Nelore cows

Three experiments evaluated effects of estradiol (E2) and/or progesterone (P4) prior to induction of ovulation with GnRH on subsequent luteal lifespan in anestrous Nelore cows. In Experiment 1, cows (25–65 days post-partum [DPP]; n = 114) were assigned randomly to receive a 6-day treatment with an intravaginal P4 device (CIDR®) and/or 1 mg i.m. injection of 17β-E2 (4 groups; 2 × 2 factorial design) prior to ovulation. Blood samples were collected on days 0, 5, 7, 9, 12, 15 and 19 for evaluation of luteal function. Pre-treatment with P4 reduced occurrence of premature luteolysis (PL; 79.2% in non-treated vs. 13.5% in treated cows; P < 0.01), but there was no effect of treatment with 17β-E2 on percentage of PL. In Experiment 2, cows (30–40 DPP; n = 35) were assigned randomly to receive either 0.5 mL i.m. injection of cottonseed oil (placebo) or 1 mg i.m. injection of E2 cypionate. Blood samples were collected on days 0, 5, 9 and 15 for evaluation of luteal function. Incidence of PL (83.0% in Control Group vs. 75.0% in ECP Group; P > 0.1) and mean serum P4 did not differ between treatment groups. In Experiment 3, cows (30–60 DPP; n = 109) were randomly assigned to receive either a 6-day (6-d Group) or a 3-day (3-d Group) treatment with CIDR®. Blood samples were collected on days 0, 5, 7 and 9 for luteal function evaluation. Incidence of PL (5.5% in 6-day vs. 5.5% in 3-day groups; P > 0.1) and mean serum P4 did not differ between treatment groups. In conclusion, both 3- and 6-day treatments with P4 prior to induction of ovulation in anestrous Nelore cows increased percentage of normal luteal lifespan, while administration of 1 mg of 17β-E2 or E2 cypionate failed to prevent occurrence of PL.