Plasma concentrations of oxytocin and intramammary pressure in goats during manual stimulation of the udder and hand-milking.

The concentration of oxytocin in the jugular venous plasma of goats was studied by radioimmunoassay and the intramammary pressure measured upon manual stimulation of the udder and hand-milking. Before stimulation the concentrations of oxytocin were close to the limit of detection, about 3 pg/ml. Manual stimulation of the udder resulted in a short-lasting increase in plasma oxytocin in 11 out of 18 experiments carried out on nine goats. There were large variations between and within individuals in the magnitude of the oxytocin increase. Hand-milking was in general as efficient stimulus for oxytocin release. In experiments in which manual stimulation had led to a large increase in plasma oxytocin, the ensuing hand-milking did not lead to a further increase. In three experiments neither manual stimulation of the udder not hand-milking resulted in any significant increase in plasma oxytocin. The intramammary pressure increased upon manual stimulation of the udder and/or hand-milking in four out of six experiments. There was, in general, a close time-relationship between changes in intramammary pressure and plasma oxytocin.