In order for lactogenesis to be maintained, milk must be removed from the mammary gland by suckling or milking.

If milk is not removed within about 16 hours in dairy cows, the synthesis of milk begins to be suppressed. As indicated previously, most of the milk in the udder of a dairy cow at the time of milking is located in the ducts and alveoli. The movement of milk into the gland cistern at suckling or milking would be slow, and less milk would be obtained during the milking of a cow, if the drainage of milk were a passive process.