We often measure blood β-hydroxybutyrate and non-esterified fatty acids in early lactation cows to diagnose excessive energy deficit on the individual cow and herd levels. In this presentation, we will discuss diurnal variation in these blood metrics and how this variation differs between hyperketonemic and non-hyperketonemic cows. Although blood measurements are a useful diagnostic method, estimates of blood and milk constituents by Fourier-transform mid-infrared analysis of milk offer a promising tool to monitor energy deficit. We will cover diurnal variation of milk constituents and discuss how monitoring of excessive energy deficit through milk has the ability to provide a more stable depiction of a cow’s transition into lactation.