MILK REMOVAL IN FAMILIAR AND UNFAMILIAR SURROUNDINGS - CONCENTRATIONSOF OXYTOCIN, PROLACTIN, CORTISOL AND BETA-ENDORPHIN

Eight cows were machine milked either in an operating theatre or in th eir familiar barn. During the experiments, milk flow curves were recor ded and blood samples were taken for determination of concentrations o f oxytocin, prolactin, cortisol and beta-endorphin. The milking cluste r was attached without udder preparation. After cessation of milk flow , air was blown into the vagina for 2 min. When milk flow had stopped again, 1 i.u. oxytocin and finally 10 i.u. oxytocin were injected to r emove the remaining milk. After the start of milking, oxytocin remaine d basal in unfamiliar, but increased in familiar surroundings. Therefo re, during normal milking only 9% of total milk was removed in unfamil iar, whereas 79% was available in familiar surroundings. In response t o subsequent vaginal stimulation in the operating theatre, oxytocin in creased transiently in five cows and 15-71% of the milk was removed in these animals. In the other three cows in the operating theatre, oxyt ocin remained basal during vaginal stimulation, and no more milk was a vailable. After injection of 1 i.u. oxytocin, 56 and 11%, and after in jection of 10 i.u. oxytocin, 13 and 8% of milk was removed in unfamili ar and familiar surroundings respectively. Concentrations of prolactin increased during the course of milking in both treatments. Premilking concentrations of cortisol and beta-endorphin were elevated in unfami liar as compared with familiar surroundings. During the course of milk ing, cortisol increased slightly and beta-endorphin decreased in unfam iliar, whereas both hormones increased markedly during milking in fami liar surroundings. We conclude that disturbed milk removal in unfamili ar surroundings is due to central inhibition of oxytocin release durin g normal milking and partly also to a response to vaginal stimulation. This blockade is possibly associated with elevated concentrations of beta-endorphin.