Effect of the genetic group, production system and sex on the meat quality and sensory traits of beef from crossbred animals.

The crossbreeding of two or more breeds from the Bos taurus and Bos indicus species is an alternative for obtaining high-quality meat from animals adapted to tropical climates. Quality and sensory attributes of beef, mainly its tenderness and flavour, are very important with regard to the consumer's point of view. This study aimed to evaluate the physico-chemical and sensory characteristics of crossbred young bulls and heifers, the offspring of Angus or Limousin bulls and 1/2 Angus + 1/2 Nellore or 1/2 Simental + 1/2 Nellore cows that were finished on feedlot or pasture. Meat quality traits (pH, colour, cooking loss, water holding capacity and shear force) and sensory parameters (characteristic beef aroma/flavour intensity, strange aroma/flavour intensity, tenderness and juiciness descriptive attributes, flavour, texture (tenderness) and overall acceptance) were evaluated. The genetic group had an effect on the beef pH, but it was not as relevant as the effect of the combination between the production system and the sex or genetic group, which affected many of the quality and sensory traits.

Variation in myogenic differentiation 1 mRNA abundance is associated with beef tenderness in Nelore cattle.

The myogenic differentiation 1 gene (MYOD1) has a key role in skeletal muscle differentiation and composition through its regulation of the expression of several muscle-specific genes. We first used a general linear mixed model approach to evaluate the association of MYOD1 expression levels on individual beef tenderness phenotypes. MYOD1mRNA levels measured by quantitative polymerase chain reactions in 136 Nelore steers were significantly associated (P ≤ 0.01) with Warner-Bratzler shear force, measured on the longissimus dorsi muscle after 7 and 14 days of beef aging. Transcript abundance for the muscle regulatory gene MYOD1 was lower in animals with more tender beef. We also performed a co-expression network analysis using whole transcriptome sequence data generated from 30 samples of longissimus muscle tissue to identify genes that are potentially regulated by MYOD1. The effect of MYOD1 gene expression on beef tenderness may emerge from its function as an activator of muscle-specific gene transcription such as for the serum response factor (C-fos serum response element-binding transcription factor) gene (SRF), which determines muscle tissue development, composition, growth and maturation.

Genome scan for meat quality traits in Nelore beef cattle.

Meat quality traits are economically important because they affect consumers' acceptance, which, in turn, influences the demand for beef. However, selection to improve meat quality is limited by the small numbers of animals on which meat tenderness can be evaluated due to the cost of performing shear force analysis and the resultant damage to the carcass. Genome wide-association studies for Warner-Bratzler shear force measured at different times of meat aging, backfat thickness, ribeye muscle area, scanning parameters [lightness, redness (a*), and yellowness] to ascertain color characteristics of meat and fat, water-holding capacity, cooking loss (CL), and muscle pH were conducted using genotype data from the Illumina BovineHD BeadChip array to identify quantitative trait loci (QTL) in all phenotyped Nelore cattle. Phenotype count for these animals ranged from 430 to 536 across traits. Meat quality traits in Nelore are controlled by numerous QTL of small effect, except for a small number of large-effect QTL identified for a*fat, CL, and pH. Genomic regions harboring these QTL and the pathways in which the genes from these regions act appear to differ from those identified in taurine cattle for meat quality traits. These results will guide future QTL mapping studies and the development of models for the prediction of genetic merit to implement genomic selection for meat quality in Nelore cattle.

Effect of α-tocopherol tissue levels on beef quality.

To evaluate meat quality of beef with different α-tocopherol tissue levels, 55 feedlot steers were fed a barley-based finisher diet with four vitamin E supplementation levels (0, 350, 700 and 1400 IU DL-α-tocopheryl acetate/animal per day) for 120 days. Although the increase in oxidation levels overtime was much smaller (P < 0.001) in the high-medium and high groups, α-tocopherol tissue levels did not affect (P > 0.05) pH, proximate analysis, drip and cooking losses, and shear force of steaks. No effect of α-tocopherol tissue levels was found in retail evaluation of steaks after a short ageing time of 6 days, but with 21 days of ageing, a delay in formation of metmyoglobin (P = 0.008) was observed in steaks with higher tissue levels of α-tocopherol. Similar results were found for ground beef (25% fat) prepared from 6-day aged meat. Thus, higher α-tocopherol tissue levels protect ground beef and long-aged steaks from discolouration and lipid oxidation.

The effects of feeding flaxseed to beef cows given forage based diets on fatty acids of longissimus thoracis muscle and backfat.

This study was conducted to investigate changes in fatty acid profiles of beef cows fed grass hay or barley silage based diets, with or without flaxseed supplementation. Both flaxseed and hay feeding increased levels of α-linolenic acid (LNA; 18:3n-3) in longissimus thoracis and backfat (P<0.001). A forage type by flaxseed level interaction was observed for most LNA biohydrogenation intermediates (P<0.05) that indicated feeding hay combined with flaxseed led to the greatest levels of total conjugated linolenic acid, total conjugated linoleic acid, total non-conjugated dienes and total trans-18:1. Predominant biohydrogenation intermediates included t11,c15-18:2, rumenic acid (c9,t11-18:2) and vaccenic acid (t11-18:1).