Equine digestion of diets based on haylage harvested at different plant maturities

Health problems in horses related to overfeeding of nutrients is increasing, but, at the same time, horses require long eating time in order to avoid development of some stereotypic behaviours. Increasing the amount of forage in the ration without increasing uptake of nutrients is therefore of interest, and was studied by examining effects of plant maturity at harvest of haylage on its digestion in horses. Haylage was harvested in June, July and August from primary growth of the same grass-dominated sward. Twelve adult horses of European warmblood type were divided into three groups and fed the haylages in a change-over experiment consisting of three consecutive periods of three weeks, so that all horses had been fed each of the haylages at the end of the experiment (9 weeks in total). The haylage diets were as close to isoenergetic (metabolisable energy) as possible for each individual horse, and average daily feeding levels were 1.4, 1.5 and 1.8 kg dry matter haylage/100 kg body weight for June, July and August haylage, respectively. Faecal samples were collected daily during the third week in each period and analysed for content of acid insoluble ash (AIA), biochemical composition and particle size distribution. Haylages were sampled and analysed for AIA content, chemical composition and nutritive value. Results showed that the dry matter digestibility was highest for June haylage (0.75) and lowest for August haylage (0.44), with July haylage (0.59) intermediate (P<0.0001). Feeding June haylage also resulted in a larger proportion of particles <0.1 mm in faeces compared to feeding July and August haylage (P<0.0001). Chemical composition and pH in faeces differed among haylage diets: when June haylage was fed, pH was lower and content of total volatile fatty acids (VFA) was higher compared to when July and August haylage was fed (P<0.0001). An effect of feeding level on digestibility could not be ruled out, as later cut haylages were fed in higher amounts than earlier cut haylage. A late harvest date of haylage made it possible to increase the amount of forage in equine diets without increasing digestibility or uptake of nutrients in horses given moderate exercise, probably due to a combination of low digestibility of mature plants and the higher feeding level needed to meet the nutrient requirements of the horse with an all or almost all forage diet.