Subcutaneous fat deposition measured as backfat thickness (BFT) increases protection for the bovine carcass during cooling, conferring to BFT an important characteristic for the meat industry. To study the influence of BFT on meat quality traits of Nellore bulls (Bos indicus), data from 1652 animals aged 20–24 months in feedlot finishing were used. The principal component analysis (PCA) was performed to characterise meat quality variables in longissimus thoracis muscle. Measurements comprised the rib eye area, BFT, marbling, shear force, myofibril fragmentation index, cooking losses, intramuscular lipid content and colour (lightness, yellowness, redness, chromaticity and hue). Considering BFT as a separation criterion, the K-means cluster analysis was applied to classify beef samples. The first four PC explained roughly 66% of total variability and meat colour (yellowness and chromaticity) was more effective to define the first PC. Tenderness or toughness (shear force and cooking losses) and fatness (BFT and intramuscular lipid content) were more effective to define the second and third PC, respectively. Three BFT groups were formed and projected in the gradient defined by PC 2 and PC 3. BFT means in the clusters were 10.82 ± 3.19 (I), 5.03 ± 1.01 (II) and 2.54 ± 0.63 (III) mm with 185, 947 and 520 animals in each group, respectively. The projection of I, II and III in the gradient allowed to distinguish fatness between beef samples and tenderness between I and III. Additionally, 57.32% of animals (Group II) were placed between the two previous groups. Beef samples with higher values of shear force and cooking losses (tough meat) showed lower BFT and myofibril fragmentation index values, possibly due to fibre shortening. PCA and K-means cluster analysis presented as interesting multivariate techniques to identify Nellore bulls regarding meat quality as some of the traits used in the study are difficult to measure. The three-cluster solution represented the main biological type of Nellore bulls finished on feedlot in Brazil showing that only 11.2% of beef samples (Cluster I) can be considered tender. This information can be useful for breeding programs of Nellore bulls. In this study, Cluster I shows optimal beef quality (SF = 4.52 ± 1.17 kg) with better marbling level and less cooking losses. Nellore cattle producers should target BFT at least 5.00 mm to prevent fibre shortening. However, the only condition which provides optimal beef tenderness (i.e. shear force values lower than 4.9 kg) was found in Cluster I. The BFT does not seem to be a suitable characteristic for the selection of animals to improve tenderness due the weak relationship between BFT and shear force.

The objective of this study was to evaluate the effect of backfat thickness (BFT) on the meat quality of feedlot-finished Nellore bulls (Bos indicus). Seventy-two animals were feedlot finished for about 100 days. For this study, 24 animals were sampled according to BFT in the longissimus thoracis muscle after slaughter: 12 animals with BFT up to 3.0 mm (class BFT-3) and 12 animals with BFT > 6.0 mm (class BFT-6). Chemical (myofibrillar fragmentation index, intramuscular fat content, and unsaturated and saturated fatty acids) and physical (cold carcass weight, rib eye area, and marbling score) characteristics of the meat were evaluated. Additionally, shear force and sensory characteristics (aroma, flavor, tenderness, chewiness, and juiciness) were analyzed. Marbling score and intramuscular fat content were considered low for the two BFT classes. The mean values of the characteristics studied did not differ (P>0.05) between BFT classes, except for fatty acids, with the observation of higher unsaturated fatty acid levels in the BFT-6 class. There was no difference (P>0.05) in sensory characteristics between BFT classes. The most consistent relationship was observed between the myofibrillar fragmentation index and tenderness, measured as shear force, in animals with greater BFT (BFT-6 class) compared to animals with lower BFT (BFT-3 class), suggesting possible tenderness problems in animals with a leaner carcass. The observation of a higher concentration of unsaturated fatty acids in animals with greater BFT suggests an increase in the sensory perception of meat, especially flavor.Keywords: sensory analysis, fat composition, muscle growth, tenderness. CARACTERÍSTICAS QUÍMICAS E SENSORIAIS DA CARNE DE BOVINOS NELORE (Bos indicus) TERMINADOS COM DIFERENTES ESPESSURAS DE GORDURA SUBCUTÂNEA NO LONGISSIMUS THORACISRESUMO: O objetivo deste estudo foi avaliar o efeito da espessura de gordura subcutânea (EGS) na qualidade da carne de bovinos machos Nelore (Bos indicus), inteiros, terminados em confinamento. Setenta e dois animais foram terminados em confinamento por cerca de 100 dias. Para o presente estudo, 24 animais foram amostrados de acordo com a EGS obtida no longissimus thoracis, após o abate: 12 animais com EGS até 3,0 mm (classe EGS-3) e 12 animais com EGS maior que 6,0 mm (classe EGS-6). Foram avaliadas características químicas da carne (índice de fragmentação miofibrilar, conteúdo de lipídeos intramusculares e ácidos graxos insaturados e saturados), e características físicas da carcaça (peso da carcaça resfriada, área de olho de lombo e escore de marmorização). Adicionalmente, foram avaliadas em amostras maturadas por 21 dias, a força de cisalhamento B. Indústr. Anim., Nova Odessa,v.72, n.4 p.341-348, 2015 CHEMICAL AND SENSORY MEAT CHARACTERISTICS OF NELLORE CATTLE... 342e características sensoriais (aroma, sabor, maciez, mastigabilidade e suculência). Os valores de escore de marmorização e de conteúdo de lipídeos intramusculares foram considerados baixos para ambas as classes de EGS. As médias das cara...

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-The objective of this work was to estimate allelic frequencies of the polymorphisms IGF2/MboII (G > T) of the insulin-like growth factor 2 (IGF2) gene, DQ499531.1:g.134A > T of the pro-melanin-concentrating hormone (PMCH) gene, and DQ667048.1:g.3290G > T of the RAR-related orphan receptor C (RORC) gene in beef cattle of different genetic groups, and to evaluate the associations between these polymorphisms and traits related to carcass composition and meat quality. Data on carcass and meat quality of 499 animals was used: of 313 Nellore (Bos indicus) and of 186 Nellore crossed with different taurine (Bos taurus) breeds. For the IGF2/MboII polymorphism, the frequencies found for the G allele were 0.231 and 0.631 for Nellore and crossed breeds, respectively. For the DQ499531.1:g.134A > T polymorphism, the allelic frequencies of A were 0.850 for Nellore and 0.905 for crossed breeds. For the DQ667048.1:g.3290G > T polymorphism, the allelic frequencies of G were 0.797 and 0.460 for Nellore and crossed breeds, respectively. The evaluated single nucleotide polymorphisms (SNPs) are not significantly associated with carcass and meat traits (rib eye area, back fat thickness, shear force, total lipids, and myofibrillar fragmentation index), suggesting little utility of the analyzed polymorphisms of the IGF2, PMHC, and RORC genes as selection markers in the studied cattle populations. Index terms: Bos indicus, beef cattle, beef quality, polymorphism. Frequências de genes candidatos e associações com característicasde carcaça e da carne em bovinos da raça Nelore e cruzadosResumo -O objetivo deste trabalho foi estimar as frequências alélicas dos polimorfismos IGF2/MboII (G > T) do gene "insulin-like growth fator 2" (IGF2), DQ499531.1:g.134 A> T do gene "pro-melanin-concentrating hormone" (PMCH) e DQ667048.1:g.3290G> T do gene "RAR-related orphan receptor C" (RORC) em bovinos de corte de diferentes grupos genéticos, e avaliar a ocorrência de associações entre esses polimorfismos e características relacionadas à composição da carcaça e à qualidade de carne.