Phenotypic relationships among somatic cell count, milk urea content, test-day milk yield and protein percent in dairy cattle

A total number of 33,881 individual test-day milk records involving 15,565 dairy cows for a 12-month period between January and December 2001 enrolled In Database Computer Center belonging to Czech Moravian Breeders Corporation, Inc., Hiradistko, The Czech Republic were used to study the phenotypic relationships among test-day milk yield (TDM), milk protein percentage (PP), protein yield (PY), somatic cell count (SCC) and milk urea content (MU) and to generate prediction regression equations to predict both SCC and MU using different independent variables in dairy cattle reared in Czech Republic using individual test-day records. Phenotypic correlations and regression coefficients were estimated using Statistical Analysis System (SAS, 2004). The overall mean (±SD) of TDM was 22.6 ± 8.50 kg, that of PP was 3.38 ±0.36%, that of PY was 0.75 ± 0.26, that of SCC was 404 ± 750 thousand cell/ml, that of somatic cell score was 3.76±1.85, that of somatic cell count transformated was 3.74 ± 1.84 and that of MU was 31.7±9.99 mg/dl. Significant (P0.001) negative correlation coefficients between TDM and each of PP (-0.42), SCC (-0.13) and SCS (-0.22), between PY and each of SCC (-0.12) and SCS (-.018) and between MU and both SCC (-0.08) and SCS (-0.09) were found. Meanwhile, there were high significant (P0.001) and positive correlation coefficients between TDM and each of PY (0.96) and MU (0.24). Prediction regression equations were generated to predict both SCC and MU using different independent variables. The significant negative correlations suggest that a lower test-day milk yield is phenotypically associated with higher somatic cell counts. It is recommended that because of association of somatic cell counts and milk yield, it may be important to consider effects of environment on somatic cell counts