The decline in dairy cow fertility over the past 30 years has major economic, welfare, genetic and environmental consequences. A significant number of potential replacement heifers either never calve or else complete only a single lactation. The relationships between metabolic status and fertility may change with age as cows reach physical maturity. To determine the reasons behind the high loss rates attributable to infertility, this study tracked a group of animals until the end of their second lactation to compare fertility and metabolic hormone profiles in the same cows at different ages.