Estimation of the cow- and herd-level prevalence of post-partum subclinical ketosis in large Washington state dairy herds and evaluation of mean β-hydroxybutyrate concentration for herd-level assessment

Abstract

The purpose of this study was to estimate the cow- and herd-level prevalence of subclinical ketosis (SCK) on dairies in the state of Washington and evaluate the arithmetic mean of individual samples as a proxy for pooled-sample testing to screen herds for SCK. The cow-level prevalence of SCK in 589 cows from 40 Washington dairies was 31,25, and 19% using P-hydroxybutyrate (BHB) concentration cutpoints of > 1.0, 1.2, and 1.4 mmol/L, respectively. For all BHB cutpoints, no difference was observed in the prevalence of SCK between cows of parity 1 and 2 (P > 0.358), but SCK was higher in cows of parity > 3 versus those in lactations 1 and 2 (P <0.001). The mean BHB concentration (mmol/L) in cows of parity > 3 (1.16) was higher than that of parity 1 (0.72) and parity 2 (0.88) cows (P <0.001). Using a BHB cutpoint of > 1.2 mmol/L and herd alarm level of >15% cows exceeding that cutpoint, 23 herds (58%) demonstrated a herd-level problem with SCK. When a BHB cutpoint of > 1.4 and herd alarm level of >25% was used, 12 herds (30%) had SCK. A herd mean BHB concentration of 0.77 mmol/L was correlated with a 15% herd-alarm level using a > 1.2 mmol/L BHB cutpoint. Sensitivity and specificity of the herd mean BHB cutpoint of >0.8 mmol/L to identify herds with > 15% cows with BHB > 1.2 mmol/L was 91 and 75%, respectively. The prevalence of SCK in Washington dairies was numerically higher than previous reports. Results of this study highlight the importance of obtaining representative samples from parity risk groups. Furthermore, results suggest parity 2 cows may be better grouped with parity 1 rather than > 3 parity cows. Herd mean BHB concentration performed well as a test to identify herds with a potential SCK problem when a mean value specific cutpoint was used. Further research evaluating the relationship between pooled-sample BHB and important outcomes, such as disease, milk production, reproduction, and removal, are needed.