Prolactin Release in Response to Milking Stimulus in the Cow and Goat Estimated by Radioimmunoassay

The effect of milking stimulus on the plasma prolactin concentration of lactating cows and goats was investigated by a radioimmunologic procedure. Plasma prolactin level in seven cows was increased abruptly 1 to 2mins. after the start of milking. On the other hand, the level of the hormone was increased shortly before the onset of milking in two cows at early lactation stage. In the goats at mid-lactation stage, milking was followed by a dramatic increase in plasma prolactin concentration within 2 mins. In all the cases, plasma prolactin level reached a peak near the end of milking. The stimuli associated with milking induced an unequivocal and rapid prolactin release from the adenohypophysis in the cow and in the goat.