Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/24/2011
Publication Date: 6/30/2011
Citation: Byrem, T.M., Erskine, R.J., Bartlett, P.C., Febvay, C., Render, C., Norman, H.D., Wright, J.R. 2011. Prevalence, transmission and impact of bovine leukosis in Michigan dairies. Journal of Animal Science 89(E-Suppl. 1)/Journal of Dairy Science 94(E-Suppl. 1):15(abstr. M32). Interpretive Summary:
Technical Abstract: Bovine leukosis, caused by infection with the retrovirus bovine leukemia virus (BLV), has been characterized as a contagious, but practically benign disease of the immune system. National Animal Health Monitoring Surveys in 1996 and 2007 indicate complacency has resulted in high prevalence of infection in US dairy herds (89%) and individual lactating cows (40%). Recent evidence that BLV infection affects immunological responses to both pathogenic challenges and vaccination increases the importance of BLV monitoring and control programs to improve overall health and productivity of dairy cows. A herd profiling index utilizing Dairy Herd Improvement (DHI) milk samples was tested for the determination of estimated BLV prevalence (EBP) and its relationship to herd management practices and productivity. Management surveys were conducted in Michigan dairy farms (113) and on DHI test date, milk samples from a subset of animals (8 <=n<=10) in each of 1st, 2nd, 3rd, and >= 4th lactations were tested for antibodies to BLV by ELISA. Correlation between BLV prevalence determined by testing all lactating animals in dairy herds (4) and by the herd profiling index was 0.997 (P<0.01). Infection with BLV was detected in 88% of the herds. Average EBP within herd was 29% (0%-76%) and within lactation, increased from 20% in 1st lactation cows to 45% in >=4th lactation cows (P<0.05). Multivariate analysis of management variables identified, recent animal purchases, some use of bull breeding, palpations per pregnancy diagnosis in heifers, and bedding use for breeding heifers as significant(P<0.05) management practices associated with EBP. For every 10% increase in EBP, rolling herd average decreased by 115±60 kg. Individual mature-equivalent (ME) lactation records were available for 3899 study animals. Significant effects of leukosis on milk, fat and protein yields were evident within all lactation groups. Across all lactation groups, BLV positive cows had lower milk (-488 kg), fat (-15 kg), and protein (-16 kg) compared to negative cows (P<0.001). Infection with BLV reduces cow productivity and is associated with purchasing replacements and breeding practices for heifers. Herd profiling using DHI milk samples is an effective strategy to determine and monitor the prevalence of infection in BLV control programs.