Abstract: The present study was made to explore the relationship between the cellular composition of somatic cells in milk of dairy cattles and parity. A total of 75 Chinese Holstein cows (from primiparous to 5th lactation) from Experimental Farm of Yangzhou University were selected and divided into 5 groups according to parity (15 cows per group). Composition of leukocytes in blood and concentrations of fat, protein, lactose, total solid, Milk Urea Nitrogen (MUN) and Somatic Cells Counts (SCC) in the milk were determined. The ratios of Macrophages (MAC), Polymorphonuclear Neutrophil Leucocytes (PMN) and Lymphocytes (LYM) in milk and peripheral blood were examined using flow cytometry and whether the ratios of the three kinds of cells was influenced by parity of the cow was then analyzed. Results showed that the percentages of MAC, PMN and LYM were 5.72~7.26, 30.10~41.10 and 50.65%~60.12% in blood, respectively and showed no significant difference among groups. The somatic cells in milk were mainly composed of MAC, PMN and LYM. The range of MAC, PMN and LYM were 11.47~22.56, 19.48~29.56 and 45.83%~63.44%. With the increase of parity, the ratios of MAC and PMN tended to be increased and LYM tended to be decreased. The results suggested that the progressive increase of SCC when parity increased might be likely related to immune mechanisms in absence of infection and resulted from increased secretion of MAC and PMN in udder. The changes of the ratios of different leukocytes to SCC in milk might provide a sensible method of indicating mammary health condition without visible infections and further understanding of generation of SCC in milk in response to parity.
A.B. Yu, G.Q. Zhao and Y.J. Huo, 2011. Relationship Between Parity and Cellular Composition of Somatic Cells in Milk of Chinese Holstein Cows. Journal of Animal and Veterinary Advances, 10: 2067-2073.