Risk factors for subclinical ketosis in grazing dairy herds in Brazil

Abstract Text:

Minimizing disease, including subclinical ketosis (SCK), continues to be a challenge for the dairy industry. Work on SCK has focused on confinement systems, with little work on pasture-based dairies. The aim of this study was to determine the prevalence and herd-level risk factors for SCK in cows housed on pasture. We visited 48 pasture-based farms in southern Brazil between February and September 2015. All farms used a rotational grazing system (2 to 3 paddocks per day). Cows (n = 13 per farm) between 3 and 21 days in milk were assessed for SCK based on blood beta hydroxybutyrate ≥ 1.2mmol/L. Data regarding number of recumbent cows up to 3 days after partum (a crude measure of milk fever) over the course of one year, supplemental feeding, and transition cow management were collected using a questionnaire by interview and environmental inspection. Herds were categorized either as Holstein or crossbred (crossbred Holstein and Jersey, or a mix of Holstein and Jersey). Herd-level prevalence of down cows was categorized into low (0-5%), medium (5-10%) and high (>10%). Herd prevalence of SCK was log transformed. Univariable linear regression models were used to select variables associated with SCK (P < 0.2). Variables from the final multivariable model were back transformed for interpretation. The overall prevalence of ketosis was 21%. Breed, down cow prevalence and access to water (free versus limited access), were retained in the final model. Referent herds had 8% (95% confidence interval (CI): 5 – 11%) SCK prevalence and consisted of Holsteins with free access to water and low prevalence of down cows. Compared to referent herds: Crossbred herds had 1.7 times higher predicted prevalence of SCK (95% CI: 1.14 - 2.55; P=0.01); limited access to water increased herd levelpredicted prevalence of SCK by 1.5 times (95% CI: 1.05 - 2.31; P=0.03) and herds with high predicted prevalence of down cows had 3 times higher prevalence of SCK (95% CI: 1.75 - 5.09; P<0.01). Pasture-based dairies appear to have similar point prevalence of SCK to confinement systems, but the risk factors are different. This work indicates that crossbred herds have higher levels of SCK, so prevention methods for SCK in these herds is especially important. Improved feeding and management that would prevent down cows and allowing cows to have free access to water should decrease the prevalence of SCK in grazing dairy herds.

Keywords:  health, hyperketonemia, transition period