Effect of corticoid induced parturition on lactation and on prepartum profiles of serum progesterone and the estrogens among cows retaining and not retaining fetal membranes

Twenty-one mature F1 Brahman-Hereford cows were treated with 25 mg of dexamethasone (DEX) on day 279 or 280 of gestation to induce birth prematurely. Eigth cows were untreated (UT). Blood was sampled on day 279 or 280 of gestation just prior to treatment of cows with DEX (0 hr), at least daily thereafter to calving and within 1 hr postpartum. Concentrations of progesterone (P₄), estrone (E₁) and estradiol-17β (Eβ) and -17α (Eα) in blood serum were measured by radioimmunoassay. Among 21 cows treated with DEX, 16 (76%) calved within 78 hr (52±3 hr). Eleven of the 16 cows retained fetal membranes more than 12 hr (RFM) and five cows did not retain fetal membranes (NRFM). Five cows (24%) treated with DEX calved 266±46 hr later (NOR) on day 290±1 of gestation compared to day 286±2 for cows in group UT. No cow in groups NOR or UT had RFM. Failure of group NOR to calve prematurely appeared due to elevated serum P₄ (P<.05), low serum Eβ (P<.10) and other estrogens (P>.10) pretreatment, and to only a 32% decrease in serum P₄ within 72 hr after treatment. Serum estrogens, especially Eβ, were next lowest pretreatment in group RFM. However, in group RFM, all serum estrogens increased (P<.10 to P<.01) within 48 hr after treatment, reached higher concentrations and peaked later in relation to calving than in other groups (NRFM, NOR and UT). Synchronization of placental maturation and parturition may require a longer period of elevated serum estrogens prior to calving than was observed in group RFM. Treatment of cows prepartum with DEX had no effect on gain of calves, milk yield or yields of fat, total protein and total solids in milk during the first 12 weeks of lactation.