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.

Castration is a common practice in beef cattle production systems to manage breeding and enhance meat quality by promoting intramuscular fat (IMF) deposition, known as marbling. However, the molecular mechanisms that are influenced by castration in beef cattle are poorly understood. The aim of this study was to identify differentially expressed genes (DEGs) and metabolic pathways that regulate IMF deposition in crossbred cattle by RNA sequencing (RNA-Seq) of skeletal muscle tissue. Six hundred and forty F1 Angus-Nellore bulls and steers (n = 320/group) were submitted to feedlot finishing for 180 days. Sixty Longissimus thoracis muscle samples were collected randomly from each group in the hot carcass (at slaughter) and 48 h post-mortem (at deboning), at between 12th and 13th thoracic vertebrae. Three muscle samples of each group were randomly selected for RNA-Seq analysis, while the post-deboning meat samples were submitted to determination of IMF content. Steers had a 2.7-fold greater IMF content than bulls (5.59 vs. 2.07%; P < 0.01). A total of 921 DEGs (FDR < 0.05) were identified in contrast between Bulls versus Steers; of these, 371 were up-regulated, and 550 were down-regulated. Functional transcriptome enrichment analysis revealed differences in biological processes and metabolic pathways related to adipogenesis and lipogenesis, such as insulin resistance, AMPK, cAMP, regulation of lipolysis in adipocytes, and PI3K-Akt signaling pathways. Candidate genes such as FOXO1, PPARG, PCK2, CALM1, LEP, ADIPOQ, FASN, FABP4, PLIN1, PIK3R3, ROCK2, ADCY5, and ADORA1 were regulated in steers, which explains the expressive difference in IMF content when compared to bulls. The current findings suggest the importance of these pathways and genes for lipid metabolism in steers with greater IMF. Notably, this study reveals for the first time the involvement of the PI3K-Akt pathway and associated genes in regulating IMF deposition in F1 Angus-Nellore cattle. Castration influenced DEGs linked to energy metabolism and lipid biosynthesis, highlighting key molecular players responsible for IMF accumulation post-castration in beef cattle.

The aim of this study was to identify differentially expressed genes, biological processes, and metabolic pathways related to adipogenesis and lipogenesis in calves receiving different diets during the cow-calf phase. Forty-eight uncastrated F1 Angus × Nellore males were randomly assigned to two treatments from thirty days of age to weaning: no creep feeding (G1) or creep feeding (G2). The creep feed offered contained ground corn (44.8%), soybean meal (40.4%), and mineral core (14.8%), with 22% crude protein and 65% total digestible nutrients in dry matter. After weaning, the animals were feedlot finished for 180 days and fed a single diet containing 12.6% forage and 87.4% corn-based concentrate. Longissimus thoracis muscle samples were collected by biopsy at weaning for transcriptome analysis and at slaughter for the measurement of intramuscular fat content (IMF) and marbling score (MS). Animals of G2 had 17.2% and 14.0% higher IMF and MS, respectively (p < 0.05). We identified 947 differentially expressed genes (log₂ fold change 0.5, FDR 5%); of these, 504 were upregulated and 443 were downregulated in G2. Part of the genes upregulated in G2 were related to PPAR signaling (PPARA, SLC27A1, FABP3, and DBI), unsaturated fatty acid synthesis (FADS1, FADS2, SCD, and SCD5), and fatty acid metabolism (FASN, FADS1, FADS2, SCD, and SCD5). Regarding biological processes, the genes upregulated in G2 were related to cholesterol biosynthesis (EBP, CYP51A1, DHCR24, and LSS), unsaturated fatty acid biosynthesis (FADS2, SCD, SCD5, and FADS1), and insulin sensitivity (INSIG1 and LPIN2). Cow-calf supplementation G2 positively affected energy metabolism and lipid biosynthesis, and thus favored the deposition of marbling fat during the postweaning period, which was shown here in an unprecedented way, by analyzing the transcriptome, genes, pathways, and enriched processes due to the use of creep feeding.