Evaluation of test-day somatic cell count of first lactation Holstein cows

Data consisting of 172,304 test-day records of first lactation Holstein cows were used to evaluate nongenetic effects on Somatic Cell Count (SCC) and Somatic Cell Score (SCS). Milk samples were collected in Holstein herds supervised by the Dairy Herd Analysis Program, at Parana State, Brazil, between January 1983 and December 1998. The statistical models included the fixed effects of region (Reg), number of milkings (NM), days in milk (DIM), age of cow (AC), month of test-day (MTD), days of storaging of samples before analysis (DS) and the random effects of herd, cow and residual. Data was analyzed by REMIL using the spatial power procedure. Observed means for SCC (x1000 cel/mL) and SCS ranged front 400,245 +/- 468,558 and 3.55 +/- 0.82 in 1993 to 241,360 +/- 514,969 and 2.41 +/- 1.35 in 1998, respectively. DIM, AC, MTD and DS effects were significant for SCC and SCS. The phenotypic correlations between SCC and SCS on consecutive test-days suggest it is possible to estabilish management routines to reduce the presence of clinical and/or subclinical mastitis in first lactation Holstein cows.