BROMOCRYPTINE IS EFFECTIVE IN REDUCING MILK-PRODUCTION IN EWES DURINGLACTATION, BUT HAS NO ADDITIONAL EFFECT DURING DRYING OFF

The effect of bromocryptine on milk production was investigated in 32 crossbred ewes (Flemish Milksheep X Suffolk) with one sucking lamb, du ring lactation and during drying off. After weaning the lambs, all ewe s were hand milked twice daily for 3 days. From day 4 onwards, the ewe s were divided into four groups with equal mean daily milk production. Ewes of groups A and B were hand milked twice daily during the follow ing 9 days. Ewes of groups C and D were dried off by reducing the milk ing frequency. They were milked on days 5, 8 and 12. In groups B and D , bromocryptin (1 ml of 1 g/l ethanol 50%) was injected intramuscularl y twice daily while control ewes (groups A and C) received 1 ml ethano l 50%. Blood samples were taken by venipuncture prior to each injectio n and were assayed for prolactin, growth hormone, thyrotropin and cort isol. Bromocryptine decreased plasma prolactin levels but did not alte r growth hormone or cortisol concentrations during lactation or drying off. Thyrotropin levels were elevated by bromocryptine during drying off but were unaffected during galactopoiesis. During lactation the da ily milk production remained unchanged in control ewes while in bromoc ryptine-treated ewes a proportional decrease of 0.5 was observed. In a ll ewes the decrease in milk production occurring at drying off could not be accelerated or stimulated by bromocryptine. It is concluded tha t prolactin plays an important role in galactopoiesis in ewes but its role is comparatively unimportant compared with other factors during m ammary involution.