A Multi-faceted Approach to the Exploration of Ketosis in Dairy Cattle: Detection, Treatment & Risk Factors
The aim of this thesis was to evaluate the diagnostic accuracy for ketosis (KET) detection methods, to estimate the prevalence of KET in Ontario, Canada and identify risk factors for increased within-herd prevalence and increased odds of KET at the cow-level. Finally, the benefit of including a glucocorticoid with propylene glycol in KET treatment was evaluated. A diagnostic test accuracy systematic review and meta- analysis was conducted for on-farm methods for the diagnosis of KET. The Precision Xtra handheld device that measures blood beta-hydroxybutyrate (BHBA) had the highest combined sensitivity (95%) and specificity (98%) of the methods evaluated. The ability of the Precision Xtra to accurately detect elevated prepartum blood BHBA at concentrations implicated in postpartum disease (0.6 to 0.8 mmol/L) was investigated. The device was moderately well correlated (0.77) with laboratory serum BHBA values, was in substantial agreement with laboratory NEFA identification of at-risk animals (κ = 0.64) and was associated with 2.2 fold greater odds of KET postpartum when prepartum BHBA ≥ 0.6 mmol/L. The within-herd and cow-level prevalence of KET was estimated to be 21% based on early lactation milk BHBA collected from herds participating in a dairy herd improvement program in Ontario, Canada. A longer calving interval, a longer dry period, being tested before 14 days in milk and having lower milk yield and fat percentages at the last test of the previous lactation was associated with increased odds of KET in multiparous animals. Increased odds of KET in primiparous animals were associated with being older at first calving. Being a Jersey increased odds of KET in all parities. Other factors associated with increased KET risk were calving in the spring and being from a herd with an automatic milking system. A randomized controlled trial evaluated the use of dexamethasone as an adjunctive therapy to propylene glycol treatment for KET. The addition of dexamethasone was associated with lower odds of KET in the week following treatment when blood BHBA was between 1.2 and 1.5 mmol/L at diagnosis, but the odds of KET after treatment were increased for the dexamethasone group when blood BHBA ≥ 3.2 mmol/L at diagnosis.