THE EFFECTS OF THE DURATION OF TREATMENTS WITH OESTROGEN AND PROGESTERONE ON THE HORMONAL INDUCTION OF MAMMARY GROWTH AND LACTATION IN THE GOAT

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Abstract
SUMMARY: The effects of the duration of hormonal treatments for inducing mammary growth and lactation were studied in ovariectomized goatlings. The injection periods were 35, 70 or 140 days for each of three hormone treatments. Treatment H: hexoestrol (0·5 mg./day); treatment HP: hexoestrol (0·5 mg./day) and progesterone (70 mg./day) and treatment HHP: treatment H for the first 40% of the period followed by treatment HP for the rest of the period. One half-udder was removed from each goat at the end of the injection period for histological examination, i.e. just before milking was started, and the other half after the peak of lactation had been attained. In general the longer the injection period the sooner were peak milk yields obtained, the interval from the beginning of the injection period to the peak yield ranging from 32 to 41 weeks. With treatment H the best yields were obtained from goats treated for only 35 days, the best yields with treatment HP were from goats treated for 140 and 70 days. On the basis of the total milk yield for the first 24 weeks of lactation, the treatment giving the highest yields was HP for 140 days; then, in descending order of efficacy, came HP for 70 days, H for 140 days, H for 35 days, HHP for 140 days, HHP for 70 days, H for 70 days, HHP for 35 days and HP for 35 days. With the exception of treatment H for 140 days, in which lactogenesis was induced during the injection period, the half-udders removed at the peak of lactation were significantly heavier than their contralateral halves removed before milking was started. Considerable growth of glandular tissue had occurred during lactation, i.e. after the hormonal treatments had ended. It is presumed that this growth is the result of the milking stimulus acting by way of the anterior pituitary; since the goats were ovariectomized ovarian hormones cannot have been involved.