While the functions of many hormones controlling milk production are known, there is little information concerning the inter-relationships between different hormones and between hormones and blood metabolites. The aim of this work was to investigate milk production, endocrine status and associated nutrient partitioning throughout lactation, in Greyface ewes rearing either single or twin lambs. Experiments were performed with ewes lambing in January and April. The seasonal differences in prolactin concentrations permits investigation of the importance of differences in concentrations of this hormone in the control of nutrient partitioning and milk production.