Effect of Milking Frequency on Mammary Functioning and Shape of the Lactation Curve

摘要

Milk yield is a function of the number of mammary secretory cells and their metabolic activity. Both are not static, but change during the course of lactation. The rate at which they change may be influenced by farm management practices, such as feeding, photoperiod, hormonal treatment (e.g., bovine somatotropin), and milking frequency. By applying such practices, or a combination thereof, at any time during lactation, the farmer has tools to alter the shape of the lactation curve. These practices could be applied after peak lactation to increase milk yield and perhaps slow down the rate of postpeak decline in milk yield, but can also be used to promote mammary involution near drying-off. The present review focuses on milking frequency. Compared with twicedaily milking, milking three times a day or more often (robotic milking) will increase milk yield by 18%, whereas once-daily milking decreases milk output by 20%. Although frequent milking is practiced more often than once daily, the once-daily milked gland provides an excellent model to study functional changes related to milking frequency. The effects of increasing and decreasing milking frequency on mammary functioning are discussed, with emphasis on functional changes in the once-daily milked gland with regard to processes such as changing cell number or activity, feedbackinhibition, tight junction leakiness, apoptosis, and cisternalalveolar milk storage.