Plasma prolactin, blood metabolites and milk production in bromocryptine-treated crossbred goats

To determine the effect of bromocryptine on plasma prolactin, metabolites and milk production, six healthy crossbred goats in their second or third lactation were selected from the institute's goat herd. The goats were injected with bromocryptine @ 5 mg per day intramuscularly for a period of 5 days during 55±60 days of lactation (period I) and treatment was repeated after 14 days for an additional 5 days (period II). Blood samples were collected for 5 consecutive days before, during and after administration of bromocryptine during both periods of the study. Milk samples were collected on days coinciding with the days of blood sampling. During period I, bromocryptine administration decreased (P < 0.01) milk yields by 27.4%. After withdrawal of bromocryptine the yields increased (P < 0.01); however, during period II, bromocryptine treatment did not decrease milk yields. During period I bromocryptine treatment suppressed prolactin level (P < 0.01) which coincided with decrease in milk yield, but in period II such decreases in prolactin did not coincide with changes in milk yields. Fat content increased (P < 0.01) after bromocryptine administration in both periods. A decrease (P < 0.01) in protein and lactose content indicated a possible role of prolactin in the synthesis of these constituents by the mammary gland cell in goats. Blood glucose and NEFA were not affected by bromocryptine in period I but in period II an increase in blood glucose with a simultaneous decrease in NEFA was observed (P < 0.01).From this study it is concluded that prolactin has a role in the maintenance of milk secretion through protein synthesis by the mammary gland. However, it does not seem to have any direct role on milk fat synthesis. # 2000 Elsevier Science B.V. All rights reserved.