A forage-only diet and reduced high intensity training distance in standardbred horses

This thesis examined growth, health and performance in sixteen 1.5-3-year-old Standardbred horses fed a forage-only diet and trained to race as 3-year-olds in either a control training programme (C-group) or a training programme in which the high intensity training distance was reduced by 30% (R-group). Body condition, height, body weight, exercise heart rate (HR), veterinary treatments, health status, locomotion symmetry and days lost to training were recorded continuously. Lactate, haematocrit and HR response to a standardised exercise were measured, as was lactate threshold (VLa4). A muscle biopsy was taken yearly for each horse and analysed for glycogen content. A complementary study examined the effect of forage crude protein (CP) content on insulin response to feeding in six adult, conditioned Standardbred horses. All horses in the main study passed a preparation race, 94% qualified for races and 56% raced. Experimental horses raced to a similar extent and passed preparation and qualification races to a higher extent than their older siblings and horses of the same cohort. There was no difference between training groups with respect to race participation, post-exercise blood lactate or VLa4. R-group horses showed less pronounced cardiovascular response to training than C-group horses. There was no difference between the groups in clinical health examinations or locomotion asymmetry but R-group horses lost fewer days to training. Locomotion asymmetry in all horses increased after introduction of new speed training and high asymmetry was associated with later qualification for races. No cases of feed-related heath disorders occurred during normal management. The horses grew least as well as reported in the literature and body condition was maintained at a moderate level. Resting muscle glycogen content was within the range reported previously for concentrate-fed horses. In the study on adult horses, the CP content and the content of water-soluble carbohydrates (WSC) together explained more of the variation in insulin response to feeding than WSC content alone. It was concluded that a forage-only diet and reduced training distance can benefit health and poses no limitation to race participation, growth, body condition or muscle glycogen content in 3-year-old Standardbred horses.