The use of indicators to assess the degree of mobilisation of body reserves in dairy cows in early lactation on a pasture-based diet

The accuracy of predicting energy balance (EB) using various milk, blood, and other indicators was determined in 23 Holstein-Friesian cows that were grazing pasture in very early lactation. The concentration of milk acetone was negatively correlated (r=−0.64) with EB (p<0.05) as were β-hydroxybutyrate 6 (BHBA) (r=0.76) and non-esterified fatty acids (r=0.56) in plasma, age (r=−0.49), and mean liveweight (r=−0.46). The concentration of plasma glucose was positively correlated (r=0.79) with EB (p<0.05) as were insulin-like growth factor-1 (IGF-1) (r=0.57) in plasma and change in liveweight (r=0.39). The best prediction model for EB included plasma glucose and plasma BHBA (r=0.84). Milk acetone alone (r=0.64) formed the best prediction model as an ‘on-farm’ indicator.Milk acetone concentration was correlated (r=0.89) with plasma BHBA so that a milk acetone concentration of 0.14 mmol/L was equivalent to a blood BHBA concentration of 1.2 mmol/L (critical level for identification of cows with sub-clinical ketosis). The relationship between plasma glucose and IGF-1 was curvilinear with levels of IGF-1 rapidly increasing above a plasma glucose concentration of 3.2 mmol/L. Body condition score (BCS) converged to 4 (scale 1-8) post-partum with the loss increasing rapidly when BCS at calving was above 5.5.The results of this study confirm that milk acetone may be an accurate and practical indicator for estimating EB of cows in early lactation on a predominantly pasture-based diet. Where cows may be sampled on a once-off basis, plasma glucose and plasma BHBA together explain a large portion of the variation in EB.