Effects of Somatic Cell Counts and Milk Composition on the Coagulating Properties of Milk

Forty-two Holstein cows were selected to provide monthly milk samples with varying SCC for 1 yr. Coagulating properties of samples measured as rennet clotting time, rate of curd firming, and curd firmness at cutting were determined by a formagraph. Milk samples were analyzed for fat, protein, lactose, total solids, casein, individual caseins, urea, SCC, and pH. Least squares analyses of data, after adjustments were made for the effect of milk composition, indicated that elevated SCC were associated with a significant increase in rennet clotting time and slower rate of curd firming. An increase of SCC from 100,000 to 500,000 SCC/ml resulted in an increase of approximately 2.1 and 2.2% in RCT and K20, respectively. A further increase of SCC to above 1,000,000/ml resulted in an overall increase of 20.7 and 13.84% in RCT and K20, respectively. Regression analyses indicated that K20 was decreased by 5.42 min and curd firmness at cutting was increased by 12.92 mm for every percentage in milk casein. Rennet clotting time, rate of curd firming, and curd firmness at cutting were increased by 3.52, 3.41, min and decreased by 9.45 mm, respectively, for every unit increase in milk pH.