Prolactin levels in the blood of ruminants

: The contents of prolactin in the blood of male ruminants and dry-period, pregnant, and lactating female ruminants was studied by a radioimmunological method. The prolactin was found to take part not only in the lactation processes but in some other functions too. The utmost changes of the prolactin contents were observed during milking: the release of prolactin from the adenohypophysis is the unconditioned reflex action. The conditioning of the hormone release into the blood is also possible. Nociceptive stimulation or adrenalin administration reduce the level of the hormone. The hand milking is more adequate as compared with the machine one and results in the higher level of prolactin in the blood. The character of the prolactin contents changes in the blood makes it possible to recommend this parameter for a physiological estimation of milking apparata.