Milk somatic cells are not suitable biomarkers of lactating ruminant mammary gland function

摘要

Understanding the molecular regulation of milk production by the ruminant mammary gland may help farmers meet increasing production milestones. Investigating these mechanisms currently relies upon invasive sampling by post-mortem or biopsy. The objective of this study was to determine if milk somatic cells, shed by the gland during milking, could be used as a non-invasive source of cells to measure these mechanisms. To answer this we employed two widely used molecular techniques, biochemical indicesand quantitative polymerase chain reaction (qPCR). Experiment 1: Biochemical indices as measures of cell size, protein production capacity and efficiency were determined in milk somatic cells and mammary tissue harvested from six lactating dairy goats. Results showed protein production capacity (P = 0.03) and cell size (P = 0.03) were higher in mammary tissue compared to somatic cells while protein production efficiency was unaffected (P = 0.55). Experiment 2: Milk protein and ribosomal RNA gene expression were measured using qPCR in milk somatic cells and mammary tissue collected from three lactating dairy cows treated with growth hormone and four treated with saline. Results showed expression of all genes differed between milk somatic cells and mammary tissue. Taken together, these results indicate milk somatic cells are not suitable for measuring biochemical indices or gene expression in the lactating ruminant mammary gland.