Within-consumer preference replication achieved through systematic image manipulation was used in consumer surveys in four cities across Mexico (Mexico City, n=195; Guadalajara, n=100; Hermosillo, n=132; Veracruz, n=61) to study beef preferences. Images of beef steaks controlled for lean and fat colour, fat cover and marbling were presented to consumers to determine the characteristics used in beef choice and the levels of preference of these characteristics. The most important choice criteria were fat cover (62% preferring little fat cover) and marbling (59% preferring non-marbled). Lean colour was also important with 24% and 29% choosing light and dark red beef, respectively. Fat colour was the least important of the four attributes studied (18% and 19% choosing white and yellow, respectively), but was nevertheless important given that 43% of consumers used three or four characteristics to make their choice. Imported and domestic beef in the Mexican marketplace appear to respond to the range of consumers' beef preferences at the point of purchase.

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To assess genetic group (GGR; Bos indicus [Bi], Bos taurus [Bt] and crosses [BtxBi]) and to confirm the calpain (CAPN316 and CAPN4751) and calpastatin (CAST-T1) single nucleotide polymorphism (SNP) effects on Warner-Bratzler shear force (WBSF), 196 animals under commercial conditions were analyzed. A model was fitted including the effect of GGR and considering residuals as adjusted WBSF (aWBSF). Another model was fitted to evaluate the SNP effect on aWBSF. Allele substitution effect (α) and combined favorable alleles in CAPN and CAST on aWBSF were evaluated. GGR showed a significant effect (P < 0.0001) on WBSF; Bt and BtxBi had the lower WBSF. CAPN316 showed significant effect on aWBSF with an α = −0.549 kg. The combined effect of CAPN and CAST showed significant (P < 0.0056) reduction on aWBSF of 0.239 kg by favorable allele. The results remarked the importance of GGR and confirmed CAPN316 and combined effect of CAPN and CAST on prediction of meat tenderness. PRACTICAL APPLICATIONSKnowledge of main factors related to tenderness, as a key related factor to beef consumer satisfaction, would serve as a resource for commercial beef classification and management under slaughterhouse conditions. Confirmation on combined marker effects provides strong validation for marker-assisted management use of these technologies under industry conditions. Additionally, the presented results may be used as a reference for research in the beef industry aimed to provide improvement on beef tenderness to the final product.

Se evaluó el comportamiento productivo de cerdos sometidos a una reducción de aminoácidos en la dieta. Durante 63 días, con un total de 96 cerdos en dos bloques y con peso inicial promedio de 42.7±4.58 kg, se estudiaron seis tratamientos producto de un arreglo factorial 2 × 3 (2 dietas, CP= dieta convencional y CN= dieta reducida en aminoácidos) y (3 equipares de fitasa: 0, sin fitasa; Fitasa A y Fitasa B). Semanalmente se registró el consumo de alimento; los cerdos se pesaron en intervalos de 21 días y se midió la profundidad de grasa y del músculo largo dorsal con un ultrasonido de tiempo real al inicio y final del ensayo; en los días 10, 31 y 52 del experimento, se determinó además la concentración plasmática de nitrógeno de urea. No hubo efectos en ninguna de las variables productivas (P>0.15), excepto en la eficiencia alimenticia acumulada a los 63 días (P<0.08), donde los tratamientos con fitasa fueron superiores. En la utilización de nutrientes, sólo hubo efecto de la dieta para lisina digestible (P<0.03), pero las concentraciones plasmáticas de nitrógeno de urea fueron las mismas (P<0.18). En conclusión, reducir la concentración de aminoácidos en dietas para cerdos desde los 40 kg de peso corporal, no afecta el comportamiento productivo por su capacidad para compensar diferencias en la densidad de nutrientes por el consumo; así el uso de fitasas debe proyectarse por la liberación de P y de energía.PALABRAS CLAVE: Cerdos, Crecimiento, Comportamiento productivo, Fitasa, Aminoácidos. ABSTRACTThe objective of this study was to evaluate the productive performance of growing pigs fed reduced amino acids diets by the use of phytase. During 63 d (three 21 d feeding phases), a total of 96 pigs in two blocks (consecutive farrowing groups), of an average initial weight of 42.7 ± 4.58 kg, were randomized to six treatments which consisted of a 2 x 3 factorial arrangement (conventional diet, a positive control= CP or reduced in amino acids by the addition of phytase, a negative control= CN) and (3 leads of phytase: 0, Phytase A or Phytase B). Weekly feed intake was recorded. At start and the end of each feeding-phase pigs were weighed and fat and muscle depths were measured using real time ultrasound. At the end of each feeding phase, blood samples were drawn to determine plasma urea nitrogen. Aside for final feed efficiency, which was slightly improved by phytase (P<0.08), there were no significant effects on any of the dependent variables during the 63 d trial (P>0.15). On the efficiency of utilization of nutrients, there was an obvious effect by level of digestible lysine (P<0.03), better in the lower lysine diets, although plasma urea nitrogen levels were the same for all treatments (P<0.18). In conclusion, a slight reduction in the concentration of amino acids, nor the addition of phytase to diets for pigs from 40 kg of body weight affect productive performance due to the inherent variation of the apportion and of the requirements.

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