The Impact of Myostatin Genetic Polymorphism on Muscle Conformation in the Horse

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In this study, we tested the recent hypothesis that a previously discovered polymorphism in the myostatin (MSTN) gene could contribute to muscle mass in the Thoroughbred racehorse. The relationship between skeletal and muscle measurements was quantified and compared to the genotypic analysis of myostatin in the horse.
A sample of 101 Thoroughbred racehorses, from a variety of locations, was assessed using a previously published set of 35 body measurements. An additional 8 Thoroughbred horses were examined using a recently developed set of muscle measures in order to better quantify the muscle mass of the animals. In addition, photographs were taken of each individual horse (n=109), in order to assess the muscle conformation. Hair samples were also collected for determination of MSTN genotype. Photographs and MSTN genotype were then assessed and compared, prior to statistical analysis, in order to determine the existence and correlation between muscle conformation and the MSTN genotype. Skewed measures, and failed genotypic analyses were eliminated from statistical analysis, resulting in a total of 86 individuals.
This study demonstrated that there is no direct correlation among conformation, body measurements, muscle measurements and MSTN genotype. Horses with a polymorphism in MSTN do not exhibit phenotypic differences of the magnitude seen in MSTN alleles of cattle and dogs. Subtle changes may be detected in future work with an expanded set of measures, larger population of horses, or by controlling environmental effects due to diet and exercise. The MSTN locus is currently used as a commercial marker of performance in the Thoroughbred although the physiological mechanism of its action is unknown. This research has eliminated the possibility of gross effects on body size and conformation, though subtler changes in muscle mass may exist. We expect future studies to further this exploration in hopes of determining why the MSTN polymorphism is not associated with altered body size or conformation in the equine species.

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muscle; myostatin; MSTN; equine/horse; genetics; polymorphism


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