ABSTRACT. We examined allele and genotype frequencies for the molecular markers CAPN1 316, CAPN1 4751 and TG5, and determined whether they are associated with beef quality traits in Mexican cattle. One hundred and twenty-four longissimus dorsi muscle samples were collected from cattle from north, central and southern Mexico. CAPN1 316 and CAPN1 4751 frequencies were determined using the allelic discrimination assay and the TG5 marker was typed by PCR-RFLP. Meat quality traits included intramuscular fat content (IMF) and tenderness determined by Warner-Bratzler shear force (WBSF) at 24 h postmortem. The association test was made using a mixed model, including genotypes, genetic group, and sampling location as fixed effects. Least squares means and significant interactions were compared using least significant differences based on the mixed procedure. CAPN1 316 CC was found at a low frequency (0.03) and has been reported as a favorable genotype associated with tenderness meat. Genotype frequencies for CAPN1 4751 were similar in favorable (CC) and unfavorable (TT) genotypes (0.26 and 0.28, respectively). The TG5 CC genotype had a frequency of 0.73, while the TT genotype frequency was 0.01. The means for WBSF and IMF were 4.08 ± 1.35 kg and 5.23 ± 2.14%, respectively. Sampling site and the CAPN1 316 genotypes significantly affected WBSF (P < 0.05). Samples collected from Hermosillo, Sonora, had the lowest WBSF (P < 0.05), while those collected in Veracruz were toughest (WBSF = 5.267 kg). The effect of GG and TG5 genotypes on IMF was significant (P < 0.05). CAPN1 316 and TG5 markers were found to be significantly associated with beef quality traits and thus will be useful for Mexican beef characterization.

Se evaluó el efecto de tres marcadores genéticos localizados en los genes de hormona de crecimiento (GH), factor de crecimiento semejante a insulina-1 (IGF-1) y leptina (LEP) sobre indicadores de eficiencia alimenticia, utilizando registros de 136 toretes de las razas Charolais, Angus y Brangus durante una prueba de comportamiento productivo. El análisis de asociación entre los genotipos obtenidos y los rasgos productivos evaluados mostró un efecto significativo del marcador GH-Alu sobre CRA (p = 0.032) en la raza Angus, y sobre el peso final ajustado (p = 0.041), en la Charolais; este resultado muestra que es posible su inclusión en los esfuerzos iniciales para la determinación de fenotipos de eficiencia en México y su consecuente aplicación en las estrategias de selección y mejoramiento genético.