The transition from winter-feeding to pasture involves a considerable diet change that might compromise the health of horses. Diseases like colic as well as insulin dysregulation and pasture associated laminitis are related to diet changes and pasture intake. However, little information exist on the metabolic responses in horses on pasture. The aim of this project is to investigate how the transition from winter-feeding to spring pasture affects blood glucose-insulin concentrations and the microbial environment in the hindgut of the horse. This project will contribute with important knowledge regarding feeding horses in the diet transition period, results that will be used in the prevention and management of diseases like colic, insulin dysregulation and laminitis.