The number and activity of mammary epithelial cells, determining factors for milk production

Abstract

-The ability of ruminant mammary glands to produce milk is determined by the number of cells secreting milk and their level of activity. Changes in the number of cells in the udder occur during lactation. It has been shown that mammary cells proliferate during this process, while other cells die through apoptosis. The decline in milk production after peak lactation appears to be due to a gradual reduction in the number of milk-secreting cells, either through cell death or by the abrasion of epithelial cells during milk ejection. Other factors are also known to modify cell turnover in the udder, such as reproductive status, growth hormone treatment or milking frequency and nutrition. A description of the effects of husbandry practices makes it possible to envisage different processes for mammary tissue regeneration during lactation. Indeed, changes in milking frequency are capable of modifying the number of epithelial cells in an alveolus, while GH treatment acts on the total number of alveoli. Thus recent studies have demonstrated an heterogeneity of the processes of proliferation and cell death within the mammary gland. However, unanswered questions still remain concerning the presence of stem cells in ruminants, the lifespan of mammary epithelial cells or the relative rate of loss of mammary cells due to apoptosis and epithelial abrasion. ruminant / milk production / mammary gland / mammary cells / proliferation / apoptosis

Effect of linseed supplementation of the gestation and lactation diets of dairy ewes on the growth performance and the intramuscular fatty acid composition of their lambs

“…As the amount of CPD and hay offered to the animals was the same in both the treatments and the diets tested in this trial were isoenergetic and isonitrogenous, no changes in milk yield or nutrient composition were expected. A possible explanation for the greater milk yield in LIN/CON treatment could be a greater differentiation of udder secretory cells, which is completed at the end of gestation and within the first few days of lactation in dairy sheep (Boutinaud et al, 2004;Castañares et al, 2013), due to linseed supplementation in the gestation period. This hypothesis is supported by recent results with dairy cows offered a linseed supplement in late gestation and early lactation, where an increase in the expression of genes involved in cell proliferation of the mammary gland was evidenced (Mach et al, 2013).…”

Regulation of Mammary Development as It Relates to Changes in Milk Production Efficiency

“…Milk production potential is a function of the number of mammary epithelial cells in the gland, as well as the secretory activity of those cells (Akers, 2002;Capuco et al, 2003;Boutinaud et al, 2004). Therefore, improved lactation performance can be achieved under conditions that enhance mammary cell proliferation (or decrease apoptosis), biochemical and structural differentiation of mammary epithelium, and synthesis and secretion of milk components.…”

Performance of dairy cows milked twice daily at contrasting intervals

“…This alternation of long and short milking intervals might also explain the higher milk yield (1.9 kg for the three experiments pooled; P 5 0.08) recorded after the longest milking intervals in the TDM groups (19 h to 21.5 h) compared with the 24 h interval in ODM. The doubled number of milkings in the TDM schedule compared with ODM may have supported the activity of mammary tissue more through hormonal action (see Lollivier et al (2002) and Boutinaud et al (2004)). …”