Effects of frequent milking on milk secretion during lactation in the goat: relation to factors which limit the rate of secretion.

Goats were milked hourly with the aid of oxytocin at different stages of lactation. Udder volume and milk yield were also measured. The marked variation between goats in the time after parturition at which peak milk yield is attained and in the rate of decline after peak is illustrated. Hourly milking had a stimulatory effect on the rate of milk secretion in early lactation (before peak) and in declining lactation (after peak), in both cases at previous milk yields of 1.1 - 1.48 g/ml udder volume . d. There was no stimulatory effect of hourly milking on milk yield at or near peak lactation (yield before the experiment greater than 1.48 g/ml volume . d) or in late lactation (less than 1.1 g/ml . d). The responses of milk yield to hourly milking are discussed in relation to the factors which limit the rate of secretion. In particular, it is concluded that a stimulatory response indicates that before the experiment the rate of secretion could not have been limited directly by the arterial supply of one or more substrates for milk synthesis. It is stressed that the results were obtained under one dietary regime only.