15 Dec 2015
Ceva Animal Health
Job Title
The bovine mammary gland undergoes dramatic changes during the production cycle of the cow, writes Lorraine M Sordillo, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA.
From the drying-off to calving, the mammary gland will be required to stop milk production, rest and just before calving be prepared for the next lactation.
The bovine mammary gland is a dynamic organ that undergoes dramatic changes in functional activity during the production cycle of the cow. The shift of the mammary gland from a relatively dormant phase in non-lactating animals to vigorous milk synthesis and secretion during lactation is highly dependent upon hormonal, nutritional, and neurohormonal influences during successive reproductive cycles. Mammary gland involution can be characterised as a complex multistep process leading to the termination of lactation or the dry period of dairy cows.
Many studies have clearly documented the importance of the dry period for optimal milk production in the subsequent lactation. Although the optimal length will vary to some extent depending on numbers of lactation cycles, a dry period of 45-60 days between lactations is generally recommended to prevent milk production losses in a subsequent lactation.
Benefits derived from a dry period involve more than improvements in the cow’s nutritional status for the forthcoming lactation. Favorable effects of involution on subsequent milk yield results from regeneration and/or reactivation of secretory epithelium before the next lactation begins and optimising host defences against mastitis-causing pathogens.
The mammary gland is a complex organ composed of a network of cells and supportive stroma that communicates to control the various cycles of involution and lactation. Biosynthetic activity of alveolar epithelial cells and the total population of such cells play decisive roles in determining milk yield.
Bovine mammary gland involution progresses through two distinct stages including a gradual decline in milk production following peak lactation and abrupt cessation of the milking. The gradual decline in milk yield following peak lactation is due, in part, to a decrease in mammary cell numbers. The loss of alveolar epithelial cells during the declining phase of lactation is a result of programmed cells death or apoptosis.
Concurrent pregnancy can also influence milk yields during the declining phase of lactation. Although the precise mechanisms are not completely understood, placental-derived increased in plasma estrogen around mid-pregnancy may influence persistency of milk yield following peak lactation.
The most rapid changes in bovine mammary tissue morphology and function during involution occur at the time of abrupt milk cessation (dry period). Milk stasis and distension of secretory tissues are factors thought to contribute to mammary involution through local chemical feedback by milk constituents, formation of other inhibitory factors in secretions, and mechanical stress to cells can lead to the loss of secretory function 3, 7. The complete transition from a lactating to nonlactating state is thought to be completed 21 to 30 days after the abrupt cessation of lactation.
Download the full publication to continue reading about mammary gland changes during the cow productive cycle, mastitis susceptibility during the dry period and future considerations.
