Effect of dietary starch, fat, and bicarbonate content on exercise responses and serum creatine kinase activity in equine recurrent exertional rhabdomyolysis.

This study explored how different diets affect the metabolic responses and CK serum activity in racehorses suffering from recurrent exertional rhabdomyolysis (RER). The research demonstrated that a high-fat, low-starch diet led to significantly lower post-exercise CK activity in severely affected RER horses, compared to a low-fat, high-starch diet, with dietary bicarbonate supplementation having no notable impact on a high-starch diet.

Research Objectives and Methodology

• The researchers aimed to study how dietary components – starch, bicarbonate, and fat – can impact metabolic responses and CK (creatine kinase) serum activity in Thoroughbreds with recurrent exertional rhabdomyolysis (RER).
• They used a crossover design method in which five RER-affected horses were fed three isocaloric diets for three weeks, each with varying starch, bicarbonate, and fat content.
• The horses were exercised on a treadmill for 30 mins, five days a week. On the last day of each diet, an incremental standardized exercise test was performed.

Diet Compositions and Results

• The ‘starch diet’ included 40% digestible energy (DE) from starch and 5% from fat.
• The ‘bicarbonate-starch diet’ mirrored the starch diet but supplemented with sodium bicarbonate (4.2% of the pellet).
• The ‘fat diet’ provided 7% DE from starch and 20% from fat.
• Before the exercise test, serum CK activity was similar across all diets. However, post-exercise CK activity differed significantly. The bicarbonate-starch diet resulted in the highest activity, while the fat diet had the lowest.

Notable Findings and Conclusions

• There were discernible differences in the severity of RER among individual horses.
• Post-exercise plasma pH, bicarbonate concentration, and lactate concentration remained consistent across all diets.
• Resting heart rates before the exercise testing were significantly lower on the fat diet compared to the starch diet.
• Muscle lactate and glycogen concentrations before and after the exercise testing did not vary notably among the diets.
• The research concluded that a high-fat, low-starch diet results in significantly lower post-exercise CK activity in severely affected RER horses, compared to a low-fat, high-starch diet.
• Dietary bicarbonate supplementation, at the concentration used in this study, did not effectively mitigate the increased CK serum activity seen with a high-starch diet.