Relationship of Somatic Cell Count with Milk Yield and Composition in Chinese Holstein Population

The objective of this study was to analyze the relationship of somatic cell count(SCC)with milk yield,fat and protein percentage,fat and protein yield using analysis of variance and correlation analysis in Chinese Holstein population.The10 524 test-day records of 568 Chinese Holstein Cattle were obtained from 2 commercial herds in Xi'an region of China during February 2002 to March 2009.Milk yield,fat percentage,fat and protein yield initially increased and then dropped down with parity,whereas protein percentage decreased and SCC increased.Analysis of variance showed highly significant effects of different subclasses SCC on milk yield and composition(P< 0.01).Compared with milk yield with SCC ≤ 200 000 cells mL-1,milk yield losses with SCC of 200000-500000 cells mL-1,501 000-1000000 cells mL-1,≥1000 000 cells mL-1 were 0.387,0.961 and 2.351 kg,respectively.The highly significant negative correlation coefficient between somatic cell score(SCS)and milk and protein yield,milk yield and fat and protein percentage,protein percentage and fat yield were-0.084,-0.037,-0.061,-0.168,and-0.088,respectively(P< 0.01).The highly significant positive correlation coefficients between SCS and fat yield and fat and protein percentage,milk yield and fat and protein yield,fat percentage and protein percentage and fat yield,protein yield and protein percentage and fat yield were 0,041,0.177,0.105,0.771,0.865,0.122,0.568,0.318,and 0.695,respectively(P<0.01).There was no significant relationship between fat percentage and protein yield(P>0.05).The results of the present study first time provide the relevant base-line data for assessing milk production at Xi'an region of China.