Reasons for performing study: Horses in training tend to become inappetant; however, the mechanism responsible for this training-induced inappetance is not known.
Hypothesis: Training and/or ulcers alter the feed intake (FI) and hormonal and/or biochemical (active ghrelin, leptin, glucose, insulin and cortisol) responses to acute high intensity exercise.
Methods: Eight Standardbred mares underwent 3 interval exercise tests (IET) and 3 parallel control tests (CON) before (IET1) and after 8 weeks of training (IET2) and after treatment for gastric ulcers (IET3). Plasma samples were taken before (0 min), during (last 10 sec of velocities eliciting 40, 100 and 20% VO2max), and after (30 min, 60 min, 24 h) exercise (EX) or CON tests for RIA and colorimetric measurement of the concentrations of the above parameters. Samples were also collected before and after feeding. Horses were trained at a work intensity of 70% HRmax for 30 min/day, 5 days per week with FI measured daily.
Results: There were no changes (P>0.05) in any variable during the parallel control trials. However, there was a mismatch between FI and digestible energy (DE) requirements (P<0.05) with EX horses not meeting their DE requirements during the post training IETs. During all IETs, ghrelin, glucose and cortisol increased (P<0.05) during EX. Leptin only increased (P<0.05) during EX in the post training IETs. Insulin remained low during EX, but increased (P<0.05) post EX.
Conclusion: High intensity exercise appeared to be associated with decreases in FI and alterations of leptin and ghrelin.
Potential relevance: More research is needed to determine if there is a relationship between alterations of these hormones and changes in FI in horses that lose weight while in training.