BROMOCRIPTINE TREATMENT OF PERIPARTURIENT GOATS - LONG-TERM SUPPRESSION OF PROLACTIN AND LACK OF EFFECT ON LACTATION

British Saanen dairy goats (n = 10) were treated with bromocriptine or vehicle from day 147 of pregnancy to day 4 post partum, a treatment d uration of 8.8 +/- 1.7 d (mean +/- SEM). The periparturient prolactin surge was abolished by this treatment, but there were no significant e ffects on plasma growth hormone or insulin concentrations. Lactogenesi s was delayed in the bromocriptine-treated goats, milk yields being si gnificantly depressed (P < 0.01) for the first week of lactation. Yiel ds had recovered to control values by day 10 when prolactin concentrat ions were still significantly depressed. Mammary gland biopsies were t aken on day 4 post partum from five animals in each group. Using this tissue, no significant differences could be shown in mammary morpholog y or DNA synthesis, but the RNA: DNA ratio was significantly reduced ( P < 0.05). After week 1, there were no significant differences between bromocriptine-treated and control goats in milk yield, milk compositi on, udder volume, time of peak yield or persistence. The goats given s hort-term bromocriptine treatment at parturition showed prolonged effe cts on prolactin secretion, their seasonal prolactin rise being severe ly blunted (P < 0.001). A normal lactation is therefore not prevented in goats by a delay in lactogenesis, suppression of prolactin at partu rition or the resulting prolonged depression of circulating prolactin. Goats in established lactation given bromocriptine for 8 d showed, by contrast, a rapid recovery of plasma prolactin concentrations within 5 d post treatment. Milk yield declined significantly (P < 0.03) compa red with pretreatment values during and for 1 week after bromocriptine but then began to recover, with no significant change in vehicle-trea ted goats.