Cell Turnover and Activity in Mammary Tissue During Lactation and the Dry Period in Dairy Cows

Abstract

Milk yield of the dairy cow follows a pattern termed the lactation curve. We have investigated the cellular background for this pattern. Seven mammary biopsies were obtained from each of 10 cows: at the end of lactation (d 347, equal to d 77 before next parturition); during the dry period at d 48 (4 d after dry off); 16 d before parturition; and during lactation at d 14, 42, 88, and 172. The fraction of proliferating (staining positive for Ki-67) alveolar cells was higher during the dry period (8.6%) than during lactation (0.5%). The fraction of apoptotic (staining positive by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) alveolar cells was higher immediately after dry off (0.37%) and in early lactation (0.76%) than during other periods (0.15%). The enzyme activities of fatty acid synthetase, acetyl CoA-carboxylase, and galactosyl transferase were approximately 12-, 11-, and 4-fold higher, respectively, during lactation than during the dry period. In conclusion, mammary cell proliferation is substantial in a period near parturition but otherwise low, and apoptosis is elevated at dry off and in early lactation. The increase in apoptosis in early lactation may be due to discarding nonfunctional or senescent cells or to removal of a surplus of newly synthesized cells. The activity of selected enzymes central for milk synthesis is probably not limiting for milk production.

Effect of pregnancy and feeding level on cell turnover and expression of related genes in the mammary tissue of lactating dairy cows

“…This concurs with the observations by Smith et al (1987), who, in multiparous ewes, found that mammary progesterone binding is increased during the period of pregnancy characterized by rapid lobulo-alveolar development, i.e. in late pregnancy (Sørensen et al, 2006).…”

“…As a consequence of re-breeding of cows in the pregnant group, they were on average 276 6 10 days into lactation at the time of biopsy sampling. This has no bearing on the results, since we observed that mammary cell turnover and gene expression is relatively stable at this stage of lactation (Sørensen et al, 2006).…”

“…We have also previously found that gene expression and activity of enzymes involved in milk synthesis were not closely linked to the actual level of milk yield (Sørensen et al, 2006). It is intriguing that a-lactalbumin gene expression is not well correlated (r 5 0.08, P 5 0.79) to milk yield, because a-lactalbumin is part of lactose synthase, the first ratelimiting enzyme regulating lactose synthesis, which is the main regulator of milk volume.…”

“…Mammary biopsies were obtained from the central part of the front quarters of all cows as described by Sørensen et al (2006). All samples were characterized as parenchyma by visual analysis of the fresh biopsy.…”

Effects of bovine mammary gland biopsy and increased milking frequency on post-procedure udder health, histology, and milk yield

“…These results indicate that the biopsy procedure may cause an inflammatory reaction due to physical trauma caused by the needle. Most studies using biopsy needle or gun, or surgical methods report an absent (Annen et al, 2007) or low mastitis incidence (Farr et al, 1996;Sorensen et al, 2006). However, this may be due to the use of prophylactic antibiotics, either systemic or intramammary, pre and post-biopsy, or other factors such as installations and milking management since mastitis incidence is associated with multiple factors.…”