THE RELATIONSHIP OF MILK SOMATIC-CELL COUNT TO MILK YIELDS FOR HOLSTEIN HEIFERS AFTER 1ST CALVING

The contribution of a dilution effect to the relationship between milk yield and milk SCC was investigated using data from 24 Holsteins during the first 75 d after first calving. Bucket and quarter milk SCC were collected at weekly intervals. Individual milk weights were obtained at milking, and samples were obtained for determination of SCC. The milk weights at the corresponding a.m. milking on the following day were also obtained. A dilution effect was assumed to cause the regression of milk yield on milk SCC to diminish when adjustment was made for milk yield on the day following sampling for SCC. Regressions of milk yield on various functions of SCC decreased by about one-half when adjustment was made for the next day's milk yield, but the regressions remained significant. The observed negative relationship between milk yield and SCC may partly reflect both the true biological effects of udder inflammation and a dilution effect. The carry-over effect of SCC on milk yields measured 1 wk after cell counting was investigated, but no effect was significant.