Hormone concentrations, mammary development and milk yield in goats given long-term bromocriptine treatment in...

Ten British Saanen goats were treated daily with 5 mg bromocriptine intramuscularly from week 8 of pregnancy until week 20 (day 140). By comparison with untreated control goats (n = 8), concentrations of prolactin in plasma were suppressed throughout the treatment period and remained significantly lower until 3 days prepartum, parturition occurring on day 153 +/- 0.7 (mean +/- S.E.M., n = 10). Growth hormone concentrations were low, but the incidence of levels exceeding 1 microgram/l was increased in bromocriptine-treated goats. Plasma concentrations of placental lactogen, progesterone and oestrone sulphate were unaffected. The accumulation of pre-colostrum in the udder (lactogenesis stage I) was not affected by bromocriptine treatment in goats carrying twin fetuses, but in goats with single kids it was delayed by about 4-6 weeks to week 17 of pregnancy. Secretion could not be expressed from the udder and the concentration of alpha-lactalbumin in plasma remained low. Udder volume was significantly reduced in week 15-16 but not week 20-21 of pregnancy by bromocriptine treatment. Milk yields after 50 or 203 days of lactation were not significantly different from those in control goats. Placental lactogen concentrations in late pregnancy and udder volume in week 20-21 were the only variables measured which correlated with milk yield post partum. It is concluded that in vivo placental lactogen is an effective mammotrophic hormone, although less potent than prolactin as evidenced by the delay in lactogenesis stage I in bromocriptine-treated goats bearing single kids.