PROLACTIN IN SERUM AND MILK DURING NORMAL PREGNANCY AND LACTATION AND HORMONALLY INDUCED LACTATIO

Prolactin levels in serum and milk were measured by the method of radioimmunoassay. In goats during pregnancy, serum prolactin concentration averaged 93.1 (+OR-) 17.2 ng/ml and peaked one day before parturation at level of 416.7 (+OR-) 75.8 ng/ml. This level dropped after kidding and fluctuated during 170 days of lactation under the influence of stage of lactation and season. There were parallel changes in milk and serum levels of prolactin, while no changes in milk yield occurred. During the first 21 days of lactation, serum prolactin levels (198.2 (+OR-) 6.0 ng/ml) were higher than those for milk (93.7 (+OR-) 7.6 ng/ml), while in the most of the rest of the lactation the opposite was true. Except when the serum prolactin rose suddenly to higher levels (over 300 ng/ml), milk prolactin levels were always less than those for serum. On average, milk prolactin levels (225.4 (+OR-) 18.6 ng/ml) were higher than serum levels (211.0 (+OR-) 19.3 ng/ml) for remainder of the lactation period. Serum prolactin concentration can be predicted from knowing the level of milk prolactin and the milk production on specific day of lactation. During the first 21 days of lactation, goats had higher concentrations of milk prolactin than sheep and cows. Milk prolactin can be predicted from the day of lactation or from the daily milk yield. In naturally lactating and induced lactating cattle (.011 mg EB/kg body weight, or .0.1 mg EB + 0.25 mg p/kg body weight), a wide variation among animals was found in their response to the treatments. Some of the animals which failed to produce enough milk had higher concentrations of prolactin in plasma than their successful counterparts during the same period before induction of lactation. Heifers had higher serum prolactin than cows. Animals under the EB + P treatment had higher serum prolactin levels than those under the EB only treatment. Milk prolactin levels were higher than serum prolactin levels in all cases. Milk prolactin peaked at higher levels after parturition in normal cows than hormonally induced lactating animals and these were significantly related to milk production.