Muscle glycogen Phosphorylase (PYGM) has been shown to catalyze the degradation of glycogen to glucose-1-phosphate. The PYGM gene can contribute to providing energy to the body by disassembling the glycogen in muscle. Here, we analyzed the genomic structure and expression of the PYGM gene in the thoroughbred horse. The PYGM gene, containing several transposable elements (MIRs, LINEs, and MERs), was highly conserved in mammalian genomes. In order to understand the expression of the horse PYGM gene, we performed quantitative RT-PCR using 11 thoroughbred horse tissue samples. The horse PYGM gene was broadly expressed in all tissues tested. In particular, the highest expression of the horse PYGM gene was observed in skeletal muscle tissue relative to the other tissues. Interestingly, the horse PYGM gene contains fewer mobile elements than its human ortholog, resulting in an increase in the structural stability of the PYGM gene sequence. This study provides insights into the genomic structure of the horse PYGM gene that may be useful in future studies of its association with exercise capability.