A short herd lifespan is a significant economic loss to the dairy industry, with infertility a major cause. Conception rates to first service have fallen from around 60% in the 1970s to 40% by 2000. The re-establishment of ovarian cyclicity after calving is important in determining the timing of conception which should be around 80 days postpartum (PP) to maintain yearly calving intervals. Insulin-like growth factor-I (IGF-I) is thought to influence ovarian activity at this time. We have previously shown that pre-pubertal IGF-I levels are related to growth and can predict concentrations around first calving. This study investigated IGF-I, insulin, glucose, urea and betahydroxybutyrate (BHB) concentrations before and after first calving in typical UK herds in relation to measures of fertility during the first lactation.