Abstract

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.

GA, Lynch, ME Hunt, and DDS MacKenzie

Proceedings of the New Zealand Society of Animal Production, Volume 51, , 191-196, 1991