Five goats were milked hourly for 43 h on two occasions, on one occasion receiving injections of growth hormone (GH; 15 mg S.C.) after 4 and 28 h of the milking period and on the other occasion were untreated. Blood samples were taken before each milking, the latter facilitated by intravenous injection of oxytocin (100 m i.u.). Milk yield began to rise 4-5 h after the injection of GH and continued to rise for a further 8-9 h until a level of production 18% above the pre-treatment yield was achieved. Following the second injection of GH the yield increment was reduced such that by the end of the experiment the yield increase was 24%. In one goat the milk yield response was not sustained and these data were excluded from the above calculations. Plasma insulin-like growth factor-I (IGF-I) and insulin concentrations increased in a similar time-course to the change in milk yield following GH treatment but were relatively constant in control experiments. IGF-I and insulin content of plasma was approximately doubled by GH treatment by the end of these experiments.
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 191-196, 1991
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