The relationship between lactation and the release of prolactin and growth hormone in the goat

Abstract

Using radioimmunoassays for ovine/caprine prolactin and caprine GH, it has been possible to measure the circulating levels of these hormones under a variety of conditions in the goat and thereby attempt to determine whether or not a temporal relationship exists between the circulating concentrations of the hormones and the level of milk production. Plasma samples were obtained from pedigree British Saanen goats, each goat being housed singly in a stall and maintained on a diet of concentrates and hay. To minimize disturbance and to obtain serial samples of blood readily, an indwelling polyethylene cannula was inserted into one of the external jugular veins not less than 15 hr before the first sample was taken. The results of the experiments demonstrate quite clearly that pregnancy and parturition modify the blood concentration of prolactin in the goat and that increases in the circulating levels of both prolactin and GH are induced by the stimulus of milking.