Resistance training and the effect of feeding Carbohydrates and oils on healthy horses and horses with polysaccharide storage myopathy.

Abstract

Type 1 Polysaccharide Storage Myopathy (PSSM) is a heritable glycogen storage disease found in many breeds that is managed with low carbohydrate, high fat diet and regular exercise. The purpose of these studies was to better understand different modes of exercise and to further study dietary management of this disease. The central hypotheses of this thesis are: 1) Resistance training as provided by a water treadmill increases fitness parameters and metabolic properties of muscle tissue; 2) feeding forage with nonstructural carbohydrate (NSC) concentration >11% increases blood insulin and glucose concentrations compared to lesser NSC; 3) feeding a short odd carbon chain fat reduces muscle damage with exercise in PSSM horses.The first investigation examined the effect of resistance training via the use of a water treadmill. Healthy unfit horses performed a standardized exercise test on a conventional treadmill before and after training on an underwater treadmill for 4 weeks to measure relative fitness and the effect on muscle enzyme activities and metabolite and substrate concentrations found in gluteal and superficial digital flexor (SDF) tissue. No increase in fitness or difference in muscle enzyme activity, or concentrations of metabolite or substrates was detected with training. SDF had lower oxidative capacity and substrate concentrations when compared to gluteal tissue. iv The second investigation examined the effect of feeding hay with differing amounts of carbohydrate to healthy Quarter Horses (QH) and QH with PSSM. Hay with high and low NSC concentrations was fed to randomly assigned horses over a period of 5 days. The diets were then reversed after a 7 day washout in which medium NSC hay was fed. The insulinemic response to the high NSC forage diet were higher compared to the low NSC diet for both the control and PSSM horses. The third investigation studied the effect of feeding hay with differing amounts of carbohydrate to healthy QH and Thoroughbreds (TB). A baseline FSGIT was conducted on both groups, after which hay with different NSC concentrations was fed over a period of 5 days in a crossover block design similar to the previous study. FSGIT results showed that QHs were more insulin sensitive and had a faster rate of Sg (glucose mediated glucose disposal) than TB. QHs secreted more insulin in response to hay > 17% NSC than hays of lower NSC, and that QHs secreted more insulin than TBs in response to higher NSC hay meals. Of note, all QH were mares, all TB were geldings, so gender, along with breed differences, could be a factor in the results. The fourth investigation examined the effect of feeding odd carbon (C7) short chain oil (triheptanoin) and other more conventional feeds to healthy and QH with PSSM with exercise. Both groups were fed isocaloric diets of triheptanoin (TH) and corn oil (CO) and exercised daily on a treadmill for 3 weeks, then performed a 15 min exercise test on the last day. These horses were also fed high carbohydrate and a commercial high fat diet. The high NSC and TH diets resulted in muscle damage with exercise indicated by plasma creatine kinase activity. The high NSC diet increased citrate and lactate concentrations compared to the other diets. The high fat and corn oil diets increased the amount of serum non-esterified fatty acids available. Long chain fat supplementation and consistent exercise remain the best choice for management of PSSM. In conclusion, resistance training as provided by water treadmill use following manufacturer‘s protocol for tendon rehabilitation did not produce an increase in cardiocirculatory fitness. Feeding hay with NSC of 17% produced an increase in insulin secretion in normal horses compared with hay of lower NSC concentrations. There may be a difference in how TB and QH respond to a glucose challenge test, but the confounding factor of breed remains unexplored. Feeding an odd carbon short chain fat to type 1 PSSM horses increased muscle damage and exercise intolerance.