Objective. To estimate current US herd-level and animal-level prevalence of bovine leukemia virus (BLV) in dairy cows and\ncharacterize epidemiologic features. Design. Cross-sectional observational study design and survey. Animals. 4120 dairy cows from\n103 commercial dairy herds in 11 states across the US. Procedures. Milk samples were collected from dairy cows through routine\ncommercial sampling and tested for anti-BLV antibodies by antibody capture ELISA. Based on the ELISA results of a sample of\nan average of 40 cows per herd, within-herd apparent prevalence (AP) was estimated by a directly standardized method and by\na lactation-weighted method for each herd. Within-herd AP estimates were summarized to give estimates of US herd-level and\nanimal-level AP.Differences in AP by lactation, region, state, breed, and herd sizewere examined to characterize basic epidemiologic\nfeatures of BLV infection. Results. 94.2% of herds had at least one BLV antibody positive cow detected.The average within-herd\nstandardized AP was 46.5%. Lactation-specific AP increased with increasing lactation number, from 29.7% in first lactation cows\nto 58.9% in 4th and greater lactation cows. Significant differences were not observed based on region, state, breed, or herd size.\nConclusions and Clinical Relevance.These results are consistent with a historical trend of increasing prevalence of BLV among US\ndairy cattle. Given the findings of other studies on the negative impacts of BLV infection on milk production and cow longevity,\nthese findings are clinically relevant for veterinarians counseling dairy clients on the risks of BLV to their herds.
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