Induction of Lactation in Nonpregnant Cows by Estradiol-17β and Progesterone from an Intravaginal Sponge

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Abstract
An intravaginal sponge impregnated with 500 mg estradiol-17.beta. and 1000 mg progesterone to induce lactation in nonpregnant dairy cattle was investigated. Sponge retention (> 95%) was achieved by its attachment to a nylon collar. Treatment with the sponge for 10 days resulted in lactogenesis in 25% of treated cows compared with an 89% success rate when an adjunct injection of dexamethasone esters (20 mg i.m.) was given on day 6 or a 96% success rate when reserpine injections (2.5 mg i.m.) were given on days 6, 8 and 10 after sponge insertion. Milking was begun 12 days after sponge insertion (2 days after removal). Peak milk yield was unaffected by adjunct treatments but was greater in spring (mean 11.5 kg/day) than in autumn treated cows (mean 3 and 6 kg/day) in 2 yr of trials. Concentration of estradiol-17.beta. in plasma rose rapidly after sponge insertion to a peak similar to that in cows in late pregnancy. Measurement of estradiol-17.beta. concentration in milk indicated less, even at first milking than in commercially distributed pasteurized milk. Milk fat and protein content were higher in milk from induced lactations compared with that from normally calving cows on the same day.