Effect of fitness on glucose, insulin and cortisol responses to diets varying in starch and fat content in Thoroughbred horses with recurrent exertional rhabdomyolysis.
BACKGROUND
Recurrent exertional rhabdomyolysis (RER) occurs in fit, nervous Thoroughbreds fed high nonstructural carbohydrate (NSC) diets. Clinical signs are diminished by feeding low NSC, high fat diets; however, the mechanism is unclear.


OBJECTIVE
To determine if the glucose, insulin and cortisol response to isocaloric diets varying in fat and NSC availability differ in fit vs. unfit Thoroughbreds with RER.


METHODS
Four fit (10 weeks treadmill training) RER Thoroughbred mares were exercised and fed 3 isocaloric (121 MJ/day) diets in a 5 day/diet block design. Two high NSC concentrates, sweet feed (SF) and a processed pelleted feed (PL) and a low starch high fat feed (FAT) were used. After 24 h of rest and a 12 h fast, horses ate half their daily concentrate. Blood sampled for [glucose], [insulin] and [cortisol] was obtained before, immediately after and at 30-60 min intervals for 420 min. After 3-6 months detraining period, the block design was repeated.


RESULTS
Results for SF and PL were similar. Regardless of diet, cortisol was higher in fit vs. unfit horses. Fit horses on SF/PL had higher post prandial [insulin] and insulin:glucose ratio than unfit horses. FAT resulted in lower post prandial [glucose] and [insulin] vs. SF/PL. Higher [insulin] in fit vs. unfit horses was not seen on the FAT diet.


CONCLUSIONS
Increased post prandial [glucose], [insulin] and [cortisol] induced by high NSC, but not high fat, feeds are enhanced by fitness in RER horses. This combination may trigger rhabdomyolysis through increased excitability in RER Thoroughbreds.
University of Minnesota Veterinary Medical Center, USA. cjfinno@ucdavis.edu
C J
CJ
Finno
E
E
McKenzie
S J
SJ
Valberg
J
J
Pagan
D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001786:Blood Glucose; D004032:Diet / Q000662:veterinary*; D004040:Dietary Carbohydrates / Q000032:analysis / Q000494:pharmacology*; D004041:Dietary Fats / Q000032:analysis / Q000494:pharmacology*; D005260:Female; D006734:Horse Diseases / Q000097:blood / Q000378:metabolism; D006736:Horses; D006854:Hydrocortisone / Q000097:blood*; D007328:Insulin / Q000097:blood*; D010805:Physical Conditioning, Animal; D012206:Rhabdomyolysis / Q000378:metabolism / Q000662:veterinary; D013213:Starch / Q000737:chemistry / Q000378:metabolism
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D007328:Insulin; D013213:Starch; D006854:Hydrocortisone