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 duration of 8.8 +/- 1.7 d (mean +/- SEM). The periparturient prolactin surge was abolished by this treatment, but there were no significant effects on plasma growth hormone or insulin concentrations. Lactogenesis was delayed in the bromocriptine-treated goats, milk yields being significantly depressed (P < 0.01) for the first week of lactation. Yields had recovered to control values by day 10 when prolactin concentrations were still significantly depressed. Mammary gland biopsies were taken on day 4 post partum from five animals in each group. Using this tissue, no significant differences could be shown in mammary morphology 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 composition, udder volume, time of peak yield or persistence. The goats given short-term bromocriptine treatment at parturition showed prolonged effects on prolactin secretion, their seasonal prolactin rise being severely blunted (P < 0.001). A normal lactation is therefore not prevented in goats by a delay in lactogenesis, suppression of prolactin at parturition 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) compared with pretreatment values during and for 1 week after bromocriptine but then began to recover, with no significant change in vehicle-treated goats.
Forsyth
I A
IA
Department of Cell Biology, AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, UK.
Lee
P D
PD
D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology*; D004247:DNA / Q000096:biosynthesis; D005260:Female; D006041:Goats / Q000502:physiology*; D013006:Growth Hormone / Q000097:blood; D007328:Insulin / Q000097:blood; D007774:Lactation / Q000187:drug effects*; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism; D008892:Milk / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000187:drug effects* / Q000378:metabolism; D011388:Prolactin / Q000096:biosynthesis*; D012313:RNA / Q000096:biosynthesis; D011863:Radioimmunoassay
D007328:Insulin; D001971:Bromocriptine; D012313:RNA; D011388:Prolactin; D013006:Growth Hormone; D004247:DNA