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Research Project: Nutritional Metabolism in Mothers, Infants, and Children

Location: Children's Nutrition Research Center

Title: Milk yield differences between 1x and 4x milking are associated with changes in mammary mitochondrial number and milk protein gene expression, but not mammary cell apoptosis or "SOCS" gene expression

Author
item Alex, A. - University Of Arizona
item Collier, J. - University Of Arizona
item Hadsell, Darryl - Children'S Nutrition Research Center (CNRC)
item Collier, R. - University Of Arizona

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2015
Publication Date: 7/1/2015
Citation: Alex, A.P., Collier, J.L., Hadsell, D.L., Collier, R.J. 2015. Milk yield differences between 1x and 4x milking are associated with changes in mammary mitochondrial number and milk protein gene expression, but not mammary cell apoptosis or "SOCS" gene expression. Journal of Dairy Science. 98(7):4439-4448.

Interpretive Summary: The frequency of milk removal has a profound effect on the amount of milk that a lactating female can produce. The mechanism through which this effect occurs is poorly understood. This study compares the effect of changes in milk removal frequency in lactating dairy cows on mammary cell gene expression, the number of mammary cell mitochondria and the frequency of mammary cell death. Higher expression of milk protein genes was observed in animals with high milking frequency. Increased milking frequency also increased mammary cell mitochondrial number but had no impact on cell death. The results suggest that increase milking frequency may enhance milk production through effects on mitochondrial dynamics as well as on gene expression.

Technical Abstract: Milking frequency is known to affect milk production and lactation persistence in dairy cows. Despite this, the mechanisms underlying this effect are only partially understood. Previous work in dairy cows examining increases in milk yield due to increased milking frequency have identified changes in apoptosis and expression of genes regulating cytokine signaling. In addition, changes in mitochondrial biogenesis and function have been suggested to play a role during the lactation cycle in regulating milk production. The goal of this study was to test the hypothesis that, when maintained over an entire lactation, extreme differences in milking frequency would be reflected in differences in apoptosis, mammary mitochondrial number, and the mammary expression of genes known to inhibit cytokine signaling. Primiparous Holstein cows (n = 6) were assigned to the study 40 d before parturition after which 1 udder half was milked once daily (1x) and the other 4 times daily (4x). Mammary biopsies were collected at 15, 60, 120, and 230 d of lactation. Average milk yield from the 4x side was 3 times higher than from the 1x side. Analysis of milk composition revealed that protein, lactose, and solids-not-fat percentages were lower in 1x than 4x udder halves. Mammary cell apoptosis was not affected by milking frequency. Mammary cell mitochondrial number, as estimated by succinate dehydrogenase staining, was higher in early lactation, decreasing as days in milk increased, and with increased milking frequency. Although mammary expression of alpha-lactalbumin (LALBA) and beta-casein (CSN2) was significantly increased in 4x glands, the expression of suppressors of cytokine signaling were similar between 1x- and 4x-milked halves. These results support the conclusion that changes in milk production in response to extreme differences in milking frequency may be related to alterations in mitochondrial number and lactose synthesis, but not apoptosis.