RESUMEN
Myostatin (GDF-8) encoded by the MSTN gene is a negative regulator of muscle growth and development and belongs to the TGF-ß superfamily of secreted growth and differentiation factors. In Thoroughbred horses, an MSTN sequence polymorphism (g.66493737C>T) is associated with optimum race distance. In the present study, a genetic polymorphism of a predicted promoter of the MSTN gene was investigated in 451 horses belonging to five different breeds: Arabian, Thoroughbred, Polish Konik, Hucul and Polish Heavy Draft. Two SNPs located at g.66495826T>C and g.66495696T>C (chr;18 EquCab 2.0) showed three haplotypes previously described: [g.66495826:T, g.66495696:T], [g.66495826:T, g.66495696:C], [g.66495826:C, g.66495696:T] with frequencies 0.877; 0.101; 0.005; respectively. Analysis performed on Polish Heavy Draft indicated the occurrence of a new haplotype [g.6649582626:C, g.66495696:C] with frequency 0.016.