OBJECTIVE To develop a high-resolution melting (HRM) assay to detect the g.66493737C>T polymorphism in the myostatin gene (MSTN) and determine the frequency of 3 previously defined g.66493737 genotypes (T/T, T/C, and C/C) in warmblood horses. SAMPLES Blood samples from 23 horses. PROCEDURES From each blood sample, DNA was extracted and analyzed by standard PCR methods and an HRM assay to determine the MSTN genotype. Three protocols (standard protocol, protocol in which a high-salt solution was added to the reaction mixture before the first melting cycle, and protocol in which an unlabeled probe was added to the reaction mixture before analysis) for the HRM assay were designed and compared. Genotype results determined by the HRM protocol that generated the most consistent melting curves were compared with those determined by sequencing. RESULTS The HRM protocol in which an unlabeled probe was added to the reaction mixture generated the most consistent melting curves. The genotypes of the g.66493737C>T polymorphism were determined for 22 horses (16 by HRM analysis and 20 by sequencing); 14, 7, and 1 had the T/T, T/C, and C/C genotypes, respectively. The genotype determined by HRM analysis agreed with that determined by sequencing for 14 of 16 horses. The frequency of alleles T and C was 79.5% and 20.5%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that HRM analysis may be a faster and more economical alternative than PCR methods for genotyping. Genotyping results might be useful as predictors of athletic performance for horses.

Gene frequencies of RBC antigens were determined in Holsteins and Colombian (criollas) cattle living at 3,000 m, and in cattle descended from fighting bulls (Vacas de lidia) living at 2,500 m. These frequencies were compared with those of Holsteins, cattle native to Florida (scrub cattle), longhorns, and native cattle from Brazil (caracu cattle) living at sea level. The criollas, Vacas de lidia, scrub cows, longhorns, and caracu are descendants of original Iberian stock introduced to the Americas. We found that despite common ancestry (scrub cattle, longhorns, criollas, and caracu), genetic differences may have been derived through years of demographic isolation. The most remarkable blood-group differences were found in the high prevalence of the B system phenogroup (heritable group of antigenic factors) BQA'G'34 in the Vacas de lidia, and of the S system phenogroup U1H' in these cattle and in caracu. Furthermore, the gene frequencies differed in the Holsteins maintained at moderately high altitude (descended from Holsteins kept at sea level), and may have been reflective of the need to adapt to moderately high altitude and chronic hypoxemic conditions. Blood group polymorphism was found in all groups of cattle, although it was reduced in the Vacas de lidia, possibly because their breeding has been carefully controlled and they appear to be highly inbred.