Influence of ration composition and energy balance on blood beta-hydroxybutyrate (ketone) and plasma glucose concentrations of dairy cows in early lactation.

The effect of ration composition, with respect to concentrate, crude protein, and methionine hydroxyanalog content, on blood beta-hydroxybutyrate and plasma glucose concentrations was assessed in Holstein cows every 2 weeks over the first 6 weeks of lactation. The correlation of these metabolites with estimated energy balance, and the effects of these ration variables on this correlation were studied. High concentrate diets (60% of dry matter) compared with low concentrate diets (40% of dry matter) increased mean plasma glucose values and reduced mean blood beta-hydroxybutyrate concentration. Variation in crude protein and methionine hydroxyanalog supplementation did not affect metabolite concentration. The correlations between blood beta-hydroxybutyrate and energy balance and between plasma glucose and energy balance were weak and subject to the influence of variation in ration composition. It was concluded that plasma glucose and blood beta-hydroxybutyrate concentrations cannot be used as valid indicators of energy balance. However, it did appear that blood beta-hydroxybutyrate might be used as an indicator of the relative glucogenic potential of dairy rations and that blood concentrations of this metabolite could potentially be used to adjust factors in the ration which influence glucose availability to the cow.