The effect of varying dietary starch and fat content on serum creatine kinase activity and substrate availability in equine polysaccharide storage myopathy.

This research evaluated the impact of altering starch and fat content in the diets of horses with Polysaccharide Storage Myopathy (PSSM), focusing on its effect on creatine kinase activity and nutrient availability. The study indicates that horses affected by PSSM may benefit from a diet low in starch and high in fat content, potentially resulting in a decrease in exercise-induced muscle breakdown as this change improves the availability of free fatty acids for muscle metabolism.

Research Methodology

• The researchers conducted a study on four mares of Quarter Horse-related breeds, all diagnosed with PSSM, a genetic muscle condition in horses.
• Four isocaloric diets with varying levels of digestible energy from starch and fat were introduced to the horses over six-week periods that included four weeks of exercise. This was carried out following a 4 X 4 Latin square design, which is a statistical design used in small-scale experiments.
• After meals, the researchers collected data on glucose and insulin responses and recorded serum creatine kinase (CK) activity, glucose, insulin, free fatty acids (FFA), and beta-hydroxybutyrate (beta-HBA) four hours post exercise.
• They also tested samples from the horses’ middle gluteal muscles to check glycogen, glucose-6-phosphate, citrate synthase, 3-hydroxy-acyl-CoA dehydrogenase, lactate dehydrogenase, abnormal polysaccharide, and lipid content.

Study Findings

• The investigation revealed that the post-meal insulin and glucose response was higher for horses on diet A (high in starch) as opposed to diet D (low in starch).
• Moreover, Creatine Kinase activity logarithmically increased with diets high in starch content (diets A, B, and C) versus the low starch diet D.
• Daily insulin was higher and FFA lower on diet A compared to other diets (B, C, and D) whereas glucose level exhibited minor variations irrespective of the diet.
• The research also uncovered low muscle oxidative capacity and lipid stores in PSSM horses, and it also recorded high muscle glycogen and abnormal polysaccharide content in horses fed both high and low in starch diets (A and D).
• The study also noted individual variations in how PSSM horses responded to diets differing in starch and fat content.

Conclusion

• For horses showing clinical symptoms of PSSM, a diet that contains less than 5% digestible energy from starch and more than 12% from fat may help reduce exertional rhabdomyolysis – a muscle disorder in horses typically due to intense exercise or overworking.
• This proposed dietary recommendation is based on the notion that increasing the availability of free fatty acids for muscle metabolism may aid in minimising muscle breakdown in PSSM horses. However, further research is required to validate these findings, due to the individual variations observed in the study.