The Importance of Prolactin and the Milking Stimulus in the Artificial Induction of Lactation in Cows

Abstract

Lactations were successfully induced in 15 out of 18 non-pregnant cows treated with oestradiol-17P (0·1 mg/kg body weight) and progesterone (0·25 mg/kg body weight) on days 1-7 (where day 1 is the first day of treatment). A further 23 out of 26 cows were successfully treated with oestradiol-17 p and progesterone standardized at 40 and 100 mg/day respectively. No significant differences in milk yields were obtained by the additional treatments of twice daily milking from day 10, sustained elevation or suppression of plasma prolactin during the induction phase by reserpine and bromocryptine respectively, or by continuing oestradiol-17 p injections alone on days 8-11. Levels of plasma prolactin less than 20 ng/mI were adequate for the preparation of the mammary gland for lactation to occur. The induced lactations of 24 monozygotic twin cows ranged from 20 to 87 % of their respective siblings which had normal parturient lactations.