Reliability of ultrasound-measured muscle thickness of the longissimus dorsi muscle in Thoroughbreds

Abstract

The purpose of this study was to determine the reliability of B-mode ultrasound measured muscle thickness of the longissimus dorsi muscle in horses. Thirteen Thoroughbreds (5 colts, 5 fillies and 3 mares) had their muscle thickness measured by B-mode ultrasound at four sites; the longissimus dorsi (LD at 30%, 50% and 70% of back length) and extensor carpi radialis (ECR) muscle on two separate test sessions (T1 and T2). Paired t-tests revealed that there was no systematic bias in any of the muscle thickness measures. There were high intraclass correlation coefficients between the LD muscle thickness at 30, 50 and 70% of back length obtained at the T1 and T2 measurements (range: 0.95-0.98). The ECR muscle thickness was positively correlated to body weight and fat-free mass while LD muscle thickness at 50% and 70% of back length did not correlate to body dimensions. Our results suggest that ultrasound measures of muscle thickness of the LD and ECR muscles are reliable and repeatable when taken with the horse standing in a relaxed and evenly balanced position.