Abstract
Reasons for performing studyAlthough muscle mass strongly influences performance, there is currently no effective means to measure the 3-dimensional muscle mass of horses. We evaluated a 3-dimensional (3D) scanning methodology for its ability to quantify torso and hindquarter volumes as a proxy for regional muscle mass in horses.ObjectivesDetermine the repeatability of 3D scanning volume (V) measurements and their correlation to body weight, estimated body volume and muscle/fat ultrasound (US) depth.MethodsHandheld 3D photonic scans were performed on 16 Quarter Horses of known body weight 56 days apart (n = 32 scans) with each scan performed in duplicate (n = 32 replicates). Tail head fat, gluteal and longissimus dorsi muscle depths were measured using US. Processed scans were cropped to isolate hindquarter (above hock, caudal to tuber coxae) and torso (hindquarter plus dorsal thoracolumbar region) segments and algorithms used to calculate V. Torso and hindquarter volume were correlated with body weight and US using Pearson’s correlation and with estimated torso volume (50% body weight / body density) with Bland-Altman analysis.ResultsScans took 2 min with < 3.5% error for duplicate scans. Torso volume (R = 0.90, P< 0.001) and hindquarter volume (R = 0.82, P< 0.001) strongly correlated with body weight and estimated BV (R = 0.91) with low bias. Torso volume moderately correlated to mean muscle US depth (R = 0.4, P< 0.05) and tail head fat (R = 0.42, P< 0.01). Mean muscle US depth moderately correlated to body weight (R = 0.50, P< 0.01).Main limitations3D Scans determine body volume not muscle volume.ConclusionsThe hand-held 3D scan provided a rapid repeatable assessment of torso and hindquarter volume strongly correlated to body weight and estimated volume. Superimposition of regional scans and volume measures could provide a practical means to follow muscle development when tail head fat depth remain constant.
Highlights
The volume (V) of the locomotor muscles in terms of number of fibers and their architectural arrangements exert a profound influence on performance by impacting the power generated by muscle at varying velocities of shortening [1; 2]
The hand-held 3D scan provided a rapid repeatable assessment of torso and hindquarter volume strongly correlated to body weight and estimated volume
Athletic horses are reported to have greater muscle mass (53–57%) when compared to other horses (42%) and a larger portion of their overall muscle weight endowed in the propulsive locomotor muscles of the hindlimb region [3]
Summary
The volume (V) of the locomotor muscles in terms of number of fibers and their architectural arrangements exert a profound influence on performance by impacting the power generated by muscle at varying velocities of shortening [1; 2]. Photographs, body condition scoring and ultrasonography (US) have been used to as a proxy to assess muscle mass in research studies of horses [2; 4; 5]. The subjectivity of body condition scoring and the limited number of muscles that can be assessed in 2 dimensions with US impede the accurate measurement of muscle development in the entire body [2; 5; 6]. Magnetic resonance imaging (MRI) is capable of providing a 3D assessment of muscle mass, it is has not yet been used to report body V or muscle mass in horses and is neither readily available, nor affordable for routine follow up [7]
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