Abstract Carcass quality traits and the Longissimus thoracis (LT) and semitendinosus (ST) muscles, aged for 2 or 14 d, from sixty castrated (CM) and non-castrated (NCM) Brangus males, slaughtered at 16 (M16) or 20 (M20) mo of age (391 and 434 kg live weight; 3.81 and 4.25 mm backfat thickness respectively), were evaluated. The carcasses of castrated and younger animals weighed less than those of non-castrated and older ones (P<0.001). Castration produced more subcutaneous fat and lower rib eye areas (P<0.05). Temperature and pH decline was faster in younger animals, and final pH was lower in castrated (P< 0.05). While the Warner Bratzler Shear Force (WBSF) of LT was 9 % lower in castrated, and 7 % higher in younger animals (P<0.05); it decreased with a longer aging period (P<0.001). The WBSF of LT was positively associated with total collagen content (r= 0.54; P<0.01) and negatively with myofibrillary fragmentation index (r= -0.39; P<0.05). The WBSF of ST was not affected by animal castration or slaughter age (P>0.05), but decreased with a longer aging period (P<0.001), and was positively associated with total collagen content (r= 0.61; P<0.05). Both muscles from castrated slaughtered at younger ages had the higher L* values. It is concluded that castration and age at slaughter on Brangus males produced differences on WBSF values only on LT muscle where collagen is not the main determinant of shear force.

Resumen Se evaluaron los rasgos de calidad de la canal y los músculos Longissimus thoracis (LT) y semitendinoso (ST), madurados durante 2 o 14 días, de sesenta machos Brangus castrados (MC) y no castrados (MNC), sacrificados a los 16 (M16) o 20 (M20) meses de edad (391 y 434 kg de peso vivo; 3.81 y 4.25 mm de grosor de la grasa dorsal, respectivamente). Las canales de los animales castrados y más jóvenes pesaron menos que las de los no castrados y de mayor edad (P<0.001). La castración produjo más grasa subcutánea y áreas del ojo de la costilla menores (P<0.05). La disminución de la temperatura y el pH fue más rápida en los animales más jóvenes, y el pH final fue menor en los castrados (P<0.05). Mientras que la Fuerza de Cizalla de Warner-Bratzler (FCWB) de LT fue 9 % menor en los castrados, y 7 % mayor en animales más jóvenes (P<0.05); disminuyó con un período de maduración más largo (P<0.001). La FCWB de LT se asoció positivamente con el contenido de colágeno total (r= 0.54; P<0.01) y negativamente con el índice de fragmentación miofibrilar (r= -0.39; P<0.05). La FCWB de ST no se vio afectada por la castración o la edad de sacrificio del animal (P>0.05), pero disminuyó con un período de maduración más largo (P<0.001), y se asoció positivamente con el contenido de colágeno total (r= 0.61; P<0.05). Ambos músculos de castrados sacrificados a edades más tempranas presentaron los valores más altos de L*. Se concluye que la castración y la edad de sacrificio en machos Brangus produjeron diferencias en los valores de FCWB solo en el músculo LT, donde el colágeno no es el principal determinante de la fuerza de cizalla.

The activity of the calpains/calpastatin proteolytic system is closely related to the postmortem tenderization of meat. We investigated the association between beef tenderness and single nucleotide polymorphism (SNP) markers on the CAPN1 gene (SNP316, alleles C/G; SNP530 alleles A/G) and the CAST gene 3' untranslated region (SNP2870, alleles A/G). We sampled nine slaughter groups comprising 313 steers which had been reared in beef production systems in Argentina between 2002 and 2004 from crosses between Angus, Hereford and Limousin cattle. Minor allele frequencies for the markers were 0.27 to 0.46 (C), 0.02 to 0.18 (A), and 0.24 to 0.53 (A), respectively. The presence of CAPN1 markers had significant effects on meat shear force but no detectable effects were demonstrated for the CAST marker. The shear force of meat from steers with the SNP316 CC genotype was 11% lower than for the SNP316 CG genotype and 17% lower than for the SNP316 GG genotype. There were very few steers with the SNP530 AA genotype and, contrary to previous studies, meat from steers with the SNP530 GG genotype showed an 11.5% higher shear force than that from steers with the SNP530 GA genotype. Final body weight, carcass weight and rib eye area were not affected by any of the markers. These results support the concept that CAPN1 variants are associated with tenderness across a wide range of beef production systems.