The effect of length of dry period upon milk secretion

The fact that dairy cows should have a dry period before calving has been recognized for quite some time. The dry period or rest period as it is sometimes called makes it possible for the cow to rebuild in her buddy the store of nutrients which she has drawn upon during the previous lactation. It is also known that as a cow progresses toward the end of her lactation the secreting cells of the mammary gland begin to involute or their functioning activity is greatly reduced. It is supposed that a dry period is necessary for recuperation and development of the mammary gland.

Recommendations of the length of dry period have ranged from thirty to sixty days. These recommendations have been based on survey studies. Very few experimental studies of effect of dry period on lactation have been reported. One way to determine the effects of the length of dry period on the udder would be to compare half udders on the same cow with different dry periods. This study was undertaken to measure the effects of varying the length of dry period of each half of the udder on the milk yields during the following lactation. An additional study of the total milk yields from twin heifers having either a normal dry period or no dry period was made, and these results compared to the study of half udders.