There is considerable confusion in some lactation studies as to the meaning of the term milk yield. Furthermore, the various fractions of milk yield are ill defined. This note proposes a standardization of terminology on this subject. The problem is general and applies to all mammals. We will discuss it, however, in terms of the dairy sheep, the animal with which we are most familiar.

I.C.I. 79,939, a potent analogue of prostaglandin F2a, was used to induce and synchronize parturition in seven gilts and three sows. A total dose of up to 750 μg injected intra-muscularly during a treatment period of about 24 h on days 109–111 of gestation induced parturition approximately 26 h after the start of treatment. The length of gestation, which was 114 ± 0·2 days in 147 normal untreated pigs, was significantly reduced to 111 ± 0·2 days (P < 0·01) in ten pigs in the same herd treated with I.C.I. 79,939. In this trial, no side-effects were detected, the average birth and 3-week weights of piglets were within the normal range, and sows usually returned to normal oestrus within a week after weaning.