Energy balance is often considered to be a major factor in the onset of dairy cow reproductive activity in early lactation. The relationships between various aspects of energy balance (EB) and the day of first heat (DFH) are weak when analysed with the mixed generalised linear model approach (e.g. Butler et al., 1981). This is understandable since DFH may not respond to the additivity of the factors which influence it but may require various states to be reached together before the expression of heat occurs. This study investigates a number of factors which may combine to influence DFH to see which combinations appear to be critical for first heat to occur. The aim of this study was to see if an alternative approach to investigating the link between energy balance and day of first heat would provide a stronger relationship than currently found with the mixed model approach.