Development and Evaluation of a Muscle Atrophy Scoring System (MASS) for Horses.
Authors: Herbst Alisa C, Johnson Mackenzie G, Gammons Hayley, Reedy Stephanie E, Urschel Kristine L, Harris Patricia A, Adams Amanda A
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Muscle Atrophy Scoring System for Equine Practice Skeletal muscle loss in horses carries significant implications for performance and welfare, yet practical assessment methods accessible to non-specialists remain limited. Herbst and colleagues developed a simple visual scoring system (MASS) to evaluate muscle atrophy across four body regions and tested its reliability across three independent raters assessing 38 horses of varying ages, breeds, and health statuses. The neck, back, and hindquarter regions demonstrated good-to-excellent inter-rater agreement (intraclass correlation coefficients of 0.62, 0.62, and 0.76 respectively), whilst the abdominal region showed poor agreement and was excluded; notably, heavier horses displayed significantly less atrophy across all three retained regions, and advancing age was positively correlated with increased atrophy scores in the neck (β = 0.030), back (β = 0.037), and hindquarters (β = 0.040). Horses with pituitary pars intermedia dysfunction exhibited higher atrophy scores than unaffected individuals even when age differences were controlled for, suggesting the system's sensitivity to clinically meaningful muscle loss. For farriers, veterinarians, and equine therapists, MASS offers a straightforward visual assessment tool that requires no specialist equipment or training, making routine monitoring of muscle status feasible in practice settings—particularly valuable for tracking age-related changes, metabolic disease impacts, and rehabilitation progress.
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Practical Takeaways
- •Use the three-region MASS (neck, back, hind) as a practical, low-cost alternative to expensive muscle mass assessment methods—no specialized equipment or expert knowledge required for reliable evaluation
- •Monitor neck, back, and hind muscle condition routinely in older horses and those with PPID, as age and endocrine disease are significant drivers of muscle atrophy independent of overall body weight
- •Do not rely on total body weight alone to assess muscle status; horses can maintain weight while losing muscle mass, making visual scoring necessary for detecting atrophy
Key Findings
- •A simplified muscle atrophy scoring system (MASS) showed good-to-excellent inter-rater agreement for neck (ICC=0.62), back (ICC=0.62), and hind (ICC=0.76) regions but poor agreement for abdominal region (ICC=0.29)
- •Body weight was inversely associated with muscle atrophy scores across neck, back, and hind regions (β=-0.008 to -0.009; P<0.001), while estimated fat-free mass showed no association
- •Age was positively correlated with muscle atrophy in neck (β=0.030, P<0.01), back (β=0.037, P<0.001), and hind (β=0.040, P<0.001) regions
- •PPID-positive horses demonstrated significantly higher muscle atrophy scores than PPID-negative horses even after controlling for age (P<0.05)