Milk ejection by lactating ewes after the intramuscular injection of synthetic oxytocin.

Abstract

Since the effects of injecting oxytocin into ewes just after artificial insemination were to be tested, the experiment described was designed to determine a range of doses of synthetic oxytocin which would produce 'milk let-down' in ewes. Intramuscular injection was chosen as the most practical route of administration since it was planned to use a large number of sheep in the subsequent experiments. Martinet & Denamur (1960) have shown that both massage of the udder and i.v. injection of 10–50 m-u. oxytocin cause similar increases in intramammary pressure in goats and sheep and Debackere & Peeters (1960) and Debackere, Peeters & Tuyttens (1961) have shown that intramammary pressure in ewes was increased by distension of the vagina; a similar response was obtained by i.v. injection of 20–50 m-u. oxytocin. Since Fitzpatrick (1960) had found that oxytocin injected i.v. was 2·25 and 2·5 times more potent than when injected i.m., the