Investigating the within-herd prevalence and risk factors for ketosis in dairy cattle in Ontario as diagnosed by the test-day concentration of β-hydroxybutyrate in milk

ABSTRACT An observational study of 790 to over 3,000 herdswas conducted to estimate the within- herdprevalence and cow-level risk factors for ketosisin dairy cattle in herdsthat participate in a Dairy HerdImprovement Association (DHIA) program. Ketosisor hyperketolactia (KET) was diagnosed as milk β-hydroxybutyrate ≥0.15 mmol/L at first DHIA test when tested within the first 30 d in milk. Seven hundred ninety-five herdsproviding at least 61 first milk tests from June 2014 to December 2015 were used to estimate the provincial within- herdprevalence of KET. All herdson DHIA in Ontario (n = 3,042) were used to construct cow-level multilevel logistic regression models to investigate the association of DHIA collected variables with the oddsof KET at first DHIA milk test. Primiparous and multiparous animals were modeled independently. The cow-level KET prevalence in Ontario was 21%, with an average within- herdprevalence of 21% (standard deviation=10.6) for dairy herdsenrolled in a DHIA program. The prevalence of KET had a distinct seasonality with the lowest prevalence occurring from July to November. Automatic milkingsystems (AMS) were associated with increased within- herdprevalence, as well as increased oddsof KET in multiparous animals at first test ( oddsratio: 1.45; 95% confidence interval: 1.30 to 1.63). Jersey cattlehad over 1.46 times higher oddsof KET than Holstein cattle. Milk fat yield ≥1.12 kg/d at the last test of the previous lactation was associated with decreased oddsof KET in the current lactation ( oddsratio: 0.56; 95% confidence interval: 0.53 to 0.59). Increased days dry and longer calving intervals, for multiparous animals, and older age at first calving for primiparous animals increased the oddsof KET at first test. This study confirms previous findings that increased days dry, longer calving intervals, and increased age at first calving are associated with increased oddsof KET and is the first report of increased KET in herdswith AMS and in relation to milk fat yield at the final test of the previous lactation. Feeding management on AMS herdslikely contributes to the increased prevalence of KET and further work is required to investigate modifications to current management to minimize risk. Milk fat yield during the previous lactation may be representative of energy partitioning.