The Influences of Bovine Leukemia on Milk Quality and Yield within a Purebred Holstein Dairy Herd

Abstract

Dairy Herd Improvement (OHI) and herd health records from 1981 through 1989 were used to assess the impact of bovine leukemia virus (BLV) in a purebred Holstein herd with emphasis placed upon milk yield, percent fat, percent protein, and somatic cell counts (SCC). Completed lactations were stratified from 1 to 5 for comparison of variables. Only data of cows milking at least 210 d were analyzed, and data from all cows that seroconverted during the 8-yr period were not included.Seropositive (BL V +) cows produced more (P>0.05) milk during lactations 3 and 5 than seronegative (BLV-) cows with no significant differences in percent fat. Percent protein was significantly higher in 1 st lactation BLV- cows followed by increased SCC in milk during the 2nd lactation compared to BL V + cows. More research is needed to elucidate the manner by which BLV infection affected milk composition.Obviously the analyses conducted on milk yield, percent fat, percent protein, and SCC were the result of unique selection pressures that concentrated the higher producing BLV+ cows after the 2nd lactation. Superior BLV- cows were removed and sold for breeding stock, and those remaining were utilized to propagate more BLV-free offspring. Therefore, milk yield was indirectly influenced by the presence of BLV within this purebred dairy herd.