Induction of Lactation: Lactational, Physiological, and Hormonal Responses in the Bovine

Open Access
Publisher Website
Google Scholar
Abstract
Milk yields, physiological responses and concentrations of plasma hormones were evaluated in 24 attempts to induce lactation in nonlactating dairy cows. S.c. injections of estradiol-17.beta. and progesterone (.10 and .25 mg/kg body weight per day) for 7 consecutive days were used. Dexamethasone injections (.028 mg/kg body weight per day) on days 18-20 were given during 12 attempts at induction. Milking was initiated on day 21. All cows showed proestrus activity within 2 days after the 1st steroid injection. In 14 of 24 attempts mean daily milk production was greater than 5 kg. Actual or projected 305 days lactation milk yields were between 1859 and 5354 kg. Milk yields of 7 induced cows averaged only 73% (32-136% range) of their previous natural lactations. Dexamethasone injections increased the number of cows that produced more than 5 kg/day and milk yields were not improved. Concentrations of estradiol, estrone and progesterone in plasma were unaffected by dexamethasone, but concentrations of glucocorticoids in plasma were depressed on days 19-22. Concentrations of prolactin (peak and mean) in plasma for 6 cows each that produced greater or less than 5 kg/day did not differ. Concentrations of prolactin increased in the week following steroid injections (days 8-15) only in those cows that produced greater than 5 kg/day but were elevated in all cows during the 3rd wk.