This study evaluated the effects of guanidinoacetic acid (GAA) supplementation during the growing and finishing phases on Nellore bulls’ performance, carcass traits, and meat quality. Fifty-two Nellore bulls were randomly assigned to four treatments: control (CON, without GAA) and three GAA levels (3, 6, and 9 g/kg dry matter [DM] in the growing supplement; 0.3, 0.6, and 0.9 g/kg DM in the finishing diet). During the 280-day growing phase, bulls were kept in paddocks, while in the 74-day feedlot finishing phase, they were housed in collective pens. Body weight, average daily gain, and carcass ultrasound measurements were recorded in both phases. Feed intake was recorded daily during finishing, and carcass traits were evaluated post-slaughter. GAA supplementation during the growing phase did not affect performance or ultrasound carcass traits (p ≥ 0.12). In the finishing phase, increasing GAA doses linearly reduced body weight gain (p = 0.03) without affecting carcass traits assessed by ultrasound or post-slaughter (p ≥ 0.10). GAA supplementation linearly reduced cooking loss (p = 0.02) without influencing other meat quality parameters (p ≥ 0.11). It is concluded that, under the conditions of this study, GAA supplementation did not affect performance or carcass traits, except for reduced weight gain at the highest dose, but reduced water loss from cooked meat.

Background: Bos taurus indicus cattle is known to be temperamental and to produce beef with greater variability in terms of quality compared to beef of Bos taurus taurus. Cattle adaptability and resilience are of great importance to sustain beef production worldwide. Objective: The study aimed to understand early post-mortem metabolites among muscles with different fiber types profile of calm and excitable Nellore, as well as its relationship with fragmentation of beef aged up to 28 d. Methods: Animals were evaluated based on chute score and exit velocity to calculate a temperament index, which was used to classify them as calm or excitable. At slaughter, the pH and temperature declines of Triceps brachii (TB) and Longissimus lumborum (LL) were measured, muscles were sampled, and aged up to 28 d. Metabolites were determined, and sarcomere length and myofibrillar fragmentation index (MFI) were quantified. Metabolomics data were analyzed using a multivariate approach, while other traits were investigated through ANOVA. Results: The pH decline was affected by all three fixed effects investigated (temperament × muscle × time post-mortem: p = 0.016), while temperature decline was affected by muscle × time (p < 0.001). Metabolites differed among muscles and cattle temperament, with excitable cattle showing greater taurine abundance in LL, as well as greater creatine in TB 1 h post-mortem, based on the volcano plot. Sarcomere length and MFI results revealed faster and limited tenderization in excitable cattle beef. Conclusions: Altogether, results emphasized the upregulation of mitochondrial enzymes and reduced tenderization as determinants of inferior beef quality after prolonged aging in excitable cattle.

Background: Beef tenderness is a key quality attribute that significantly influences consumer satisfaction; however, it exhibits considerable variability due to both genetic and environmental factors. While genomic selection based on Expected Progeny Differences (EPDs) has improved the accuracy of predictions, a substantial portion of tenderness variability remains unexplained. Metabolomics has emerged as a valuable approach to address this gap, as metabolites reflect gene–environment interactions and may serve as biomarkers for complex traits such as meat tenderness. Objectives: This study aimed to integrate genomic and metabolomic data to identify genetic loci associated with serum metabolites in Nellore calves, offspring of sires with contrasting EPDs for meat tenderness. Methods: Ninety-five male calves were evaluated and divided into two groups according to the sires’ genetic merit: FA-T (favorable EPD for tenderness, n = 45) and UN-T (unfavorable EPD for tenderness, n = 46). Blood serum samples were analyzed by ¹H NMR spectroscopy to quantify 40 metabolites, and genotyping was performed using a medium-density SNP panel. Metabolite quantitative trait loci (mQTL) were identified using the MatrixEQTL package, and metabolic enrichment analysis was performed in MetaboAnalyst 6.0. Results: In the FA-T group, SNPs were associated with metabolites such as phenylalanine, tyrosine, and succinate, suggesting enhanced oxidative metabolism and preservation of proteolysis. In the UN-T group, associations of pyruvate, creatinine, and glutamine with distinct SNPs indicated greater reliance on anaerobic glycolysis and early ATP consumption, potentially impairing phosphorylation and postmortem proteolytic activity. Conclusions: These findings suggest that genetic selection for tenderness may induce early divergent metabolic profiles, likely leading to persistent differences in postmortem biochemical pathways, with important implications for meat tenderness.

Meat tenderness is a key attribute for consumer satisfaction, and the prevalence of Nellore cattle in Brazil, combined with the variability in tenderness within this breed, highlights the need for strategies to improve this trait. In this context, metabolomics emerges as a tool for understanding the biological mechanisms and identifying the metabotypes associated with tenderness. This study evaluated whether genetic selection for meat tenderness, based on expected difference in progeny (EPD), is associated with performance and serum metabotypes in Nellore calves at birth and weaning. Calves with favorable selection for tenderness (FMT) had higher birth weights and, at birth, higher concentrations of alanine, glutamate, glycine, lactate, proline, and threonine. At weaning, calves with unfavorable selection for tenderness (UMT) had higher concentrations of isoleucine and valine, as well as greater subcutaneous fat thickness and rump fat thickness. The enrichment of metabolic pathways suggested differences in energy and antioxidant metabolism at birth, as well as in the breakdown of branched-chain amino acids and propionate metabolism at weaning. Spearman’s correlation analysis identified only moderate associations in the FMT group, including a positive correlation between homoserine and weight gain ( rs = 0.416; P < 0.001) and negative correlations between glycerol and weaning weight ( rs = − 0.411; P < 0.001) and weight gain ( rs = − 0.406; P < 0.001). Overall, genetic selection for meat tenderness was associated with metabolic and phenotypic differences in Nellore calves from early life, indicating that biological effects related to selection for tenderness may be detectable early in an animal’s life.

Background: Phytogenic feed additives are being explored as alternatives to conventional rumen modulators, yet their effects on the ruminal ecosystem remain insufficiently characterized when assessed only through conventional fermentation parameters. This study evaluated the effects of ethanolic and hydroethanolic extracts of Urochloa brizantha on ruminal fermentation, methanogenic archaeal diversity, and the ruminal metabolome of sheep. Methods: Eight rumen-cannulated wethers were assigned to a replicated 4 × 4 Latin square design with four 28-day periods. Treatments consisted of no additive (CTL), ethanolic extract of U. brizantha (EE; 50 mL/day), hydroethanolic extract (HE; 80 mL/day), and monensin (MON; 25 mg/kg of DMI). Ruminal fluid was evaluated for fermentation traits, archaeal 16S rRNA gene diversity, and untargeted metabolomic profiles. Results: Dry matter intake and fermentation parameters were unaffected by treatment. Archaeal alpha diversity showed a contrast-dependent response, with lower Shannon diversity in sheep receiving plant extracts than in those receiving monensin (p = 0.034), and Methanimicrococcus was selectively enriched in the EE group (p = 0.012). Untargeted metabolomics revealed the clearest response: despite substantial overlap in global PCA profiles, PLS-DA indicated treatment-specific temporal separation between day 0 and day 21 only in EE-treated sheep, supported by permutation testing based on classification error rate (p = 0.027), although predictive performance should be interpreted cautiously. This EE-specific response was characterized by a significant shift in the carboxylic acid subclass (FDR = 0.022). Top VIP-ranked discriminants (aspartate, succinate, glutamate, phenylalanine, leucine, and choline) decreased nominally but failed multiple-testing correction (FDR = 0.0602–0.2580). CTL, HE, or MON showed no temporal separation. Conclusions: Urochloa brizantha extracts produced limited effects on conventional ruminal fermentation parameters but were associated with selective archaeal responses. In particular, the ethanolic extract was associated with a treatment-specific temporal metabolomic pattern, including a significant shift in the carboxylic acid subclass, while individual metabolite changes remained exploratory and warrant further investigation.