During lactation sows are often unable to consume sufficient feed to meet their metabolic needs and they must mobilise their body reserves to compensate for the nutrient deficit. It is generally recognised that this loss of body weight and body condition may influence subsequent reproductive performance but it is unclear what endocrine signals link the nutritional and reproductive states of the sow. The present experiments were, therefore, designed in an attempt to understand how changes in the nutritional and metabolic status of the sow during lactation influences post-weaning reproductive performance.