INFLUENCE OF MILK SOMATIC-CELL COUNT AND MILK AGE ON CHEESE YIELD

Batches (n = 22) of milk were collected from groups of 8 to 10 cows with similar milk SCC from < 100,000 to 1,300,000 cells/ml. Each batch was split into two portions and Cheddar cheese was manufactured after 1 and 5 d of refrigerated storage. Milk casein as a percentage of true protein (C%TP) and cheese yield efficiency were lower when milk SCC was high and when milk was 5 d old. Fat and protein losses in whey increased with increased milk age and SCC. Cheese moisture increased with milk SCC and decreased with milk age. It was concluded that any increase in milk SCC above 100,000 cells/ml will have a negative impact on cheese yield efficiency for milk from groups of cows with similar milk SCC. The change in cheese yield efficiency for commingled milk would not show this same trend. Herd milk will represent a weighted average of the milk characteristics from individual cows. In the second part of this study, milk was collected from 40 cows for a preliminary investigation of the influence of stage of lactation and parity on milk C%TP and SCC. There was a significant change in C%TP and milk SCC with time in lactation. Milk SCC increased from about 50,000 to near 300,000 cells/ml, and C%TP decreased from 82.4 to 79.7% with time in lactation for multiparous cows. Further work with a larger number of cows in needed to characterize the impact of parity.