Distribution of milk in the goat mammary gland and its relation to the rate and control of milk secretion.

Changes with time in the distribution of milk between different storage regions of the mammary gland were studied in goats. Milk was allowed to drain from the gland through a catheter (catheter milk); the gland was then milked by hand, before (hand milk) and after the administration of oxytocin (alveolar or residual milk). The hand-milk fraction was of negligible volume. There was an essentially linear increase in the catheter-plus hand-milk fraction from 0 to 16 h. The alveolar fraction increased up to 6 h, but thereafter remained constant to 16 h. There was considerable but consistent variation between animals in the alveolar fraction as a proportion of total milk volume. The proportion of residual milk was inversely related to milk secretory rate per unit weight of mammary tissue. The hourly administration of oxytocin without milking had no apparent effect on the distribution of milk in the gland 1 h later.