Risk factors associated with hemorrhagic bowel syndrome in dairy cattle.

OBJECTIVE To determine risk factors associated with hemorrhagic bowel syndrome (HBS) among dairy cattle in the United States and identify characteristics of HBS in individual cows. DESIGN Cross-sectional, population-based survey. SAMPLE POPULATION A stratified random sample of 1,013 dairy operations with > or = 30 cows located in 21 states. PROCEDURE Information on management and animal health-related topics was collected with a questionnaire. RESULTS HBS was estimated to have been observed on 9.1% of operations during the preceding 5 years and on 5.1% of operations during the preceding 12 months. Factors found in multivariable analysis to be associated with the occurrence of HBS during the preceding 12 months were large herd size, administration of bovine somatotropin, and routine use of milk urea nitrogen concentration to determine ration composition. Use of pasture as part of the lactating cow ration during the growing season was associated with decreased odds of HBS in operations with rolling herd average milk production < or = 20,000 lb, whereas in operations with higher milk production, use of pasture was not associated with occurrence of HBS. For individual cows with signs consistent with HBS, the third lactation was the median of the parity distribution and the median time between parturition and the onset of clinical signs was 104 days. CONCLUSIONS AND CLINICAL RELEVANCE Results suggest that management practices implemented to achieve high milk production may increase the risk of developing HBS in dairy cattle. Increased consumption of a high-energy diet seems to be the most plausible common pathway for all of the risk factors that have been described.