Fibre types, enzyme activities and substrate utilisation in skeletal muscles of horses competing in endurance rides.

The research explores the energy utilization patterns in the muscles of horses participating in long-distance endurance rides. It particularly looks at how various enzymes and fibre types in the skeletal muscle respond, and their role in metabolizing carbohydrates and lipids.

Methodology

• The study involved 21 horses, divided into three groups (A, B, C). Group A comprised seven horses participating in a 100 km ride, four of whom completed it. Group B had six horses that were among the best performers in a 50 km ride, while Group C comprised eight horses that completed the 50 km ride at a slower pace.
• Researchers collected venous blood samples and middle gluteal muscle biopsies from all participating horses. These samples were used to examine the fibre composition, fibre areas, and enzyme activities in the horses’ muscles.

Findings

• The research found an increase in levels of blood lactate, glycerol, and creatine kinase in all groups, implying heightened metabolic activity. Aspartate aminotransferase levels increased only in the horses from Group A (100 km ride).
• There was no noticeable variation in blood glucose levels in groups B and C, but this level had dipped in Group A after the ride.
• The study did not find any difference in fibre composition, fibre areas, or enzyme activities between the three groups, implying that these might be inherent characteristics not affected by the intensity of the ride.
• Comparatively, Group C showed a lesser decrease in glycogen, indicating slower metabolic rates or energy utilization. Interestingly, this group also had higher resting levels of intramuscular triglycerides compared to Group B.
• The largest decrease in the content of triglycerides after the ride was also observed in Group C, signifying the significant role these lipids play in providing energy for this group.
• In Group A and B, many Type I, IIA, and IIB fibres had depleted glycogen stores after the ride. Meanwhile, in Group C, mainly Type I and some Type IIA fibres had exhausted their glycogen stores.

Conclusion

• The results highlight that energy consumption during endurance rides involves both carbohydrate and lipid metabolism. This explains the observed changes in glycogen and triglycerides levels in horse muscles.
• The study serves as useful basis for understanding metabolic adaptations in horses during sustained physical activities and could provide insights for better training methods and diet planning.