Muscle characteristics in young Norwegian-Swedish Coldblooded Trotters and associations with breeding index, body size and early training.

Summary

# Editorial Summary Norwegian-Swedish Coldblooded Trotters have demonstrated improving trotting performance over successive generations, largely driven by selective breeding, yet little was known about the actual variation in muscle composition across the population or how this relates to breeding selection criteria. Revold and colleagues examined biopsies of the middle gluteal muscle in young NSCTs to characterise fibre type distribution, oxidative capacity and other contractile properties, then correlated these findings with individual breeding indices, body measurements and early training exposure. The study revealed considerable heterogeneity in muscle characteristics within the breed—particularly in the proportion of oxidative fibres and oxidative enzyme activity—with some associations between muscle phenotype and breeding index values, suggesting that selection strategies may be indirectly influencing muscle composition. These findings have practical implications for breeding programmes, as they indicate that genetic merit scores correlate with measurable muscular traits relevant to trotting performance; additionally, understanding natural variation in muscle physiology could help farriers, veterinarians and trainers identify individual horses' physiological strengths and tailor conditioning or nutritional support accordingly.

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Key Findings

• •Muscle parameters in Norwegian-Swedish Coldblooded Trotters show previously undescribed variability across the population
• •Middle gluteal muscle characteristics are associated with breeding index values
• •Body size and early training influences muscle development in young trotters
• •Breeding progress correlates with muscular adaptations supporting increased trotting speed

Conditions Studied