Effects of training on equine muscle fibres and monocarboxylate transporters in young Coldblooded Trotters.

The research article examines the physical changes in muscle fibres and lactate-transporters of young Norwegian-Swedish Coldblooded Trotter horses as a result of training. The study particularly investigates the distribution of the monocarboxylate transporter 1 (MCT1) and its ancillary protein CD147, which are responsible for facilitating lactate transport across cell membranes.

Research Design and Methodology

• The study followed nine horses from the beginning of their training period until they reached the end of their 3-year-old season. One horse was subsequently excluded due to lameness.
• Researchers collected muscle biopsy samples from the middle gluteal muscle of each horse on four different occasions.
• An incremental exercise test on a high-speed treadmill was conducted on the last 3 sampling occasions to determine individual V(La4)-values, which reflect the speed corresponding to a blood lactate concentration of 4 mmol/l.
• Both histochemical and immunohistochemical analyses were performed on all muscle samples. Researchers analysed the differentiation of fibre types, oxidative capacity (as measured by NADH levels) and the expression levels of MCT1 and CD147.
• The activity of selected muscle metabolic enzymes before and after training was also determined.

Findings and Results

• Training led to certain changes in muscle fibre composition – the percentage of type IIX fibres decreased while the level of IIAX fibres increased. This indicates a transition in fibre types as a response to regular training.
• Training also led to an increase in the activity of citrate synthase and 3-OH-acyl-CoA-dehydrogenase, enzymes that play a crucial role in fat and carbohydrate metabolism respectively.
• The expression of the MCT1 transporter was lower in IIX fibres compared to all other fibre types, both before and after training. This indicates a link between transporter expression and the oxidative capacity of muscle fibres.
• In terms of CD147, the protein was evident in the membranes and cytoplasm of all fibre types.
• All horses displayed an increase in the V(La4)-value over time, starting from a lower value and then increasing in the last two measurements.

Conclusions

• The muscular changes observed in the NSCT breed as a result of training align with those previously reported in the Standardbred breed. This suggests similar adaptive mechanisms at play among different horse breeds.
• The expression of the MCT1 transporter was found to vary between muscle fibre types, suggesting a relationship between transporter expression and the specific oxidative properties of these fibres.