Patricia Maloso Ramos

The variability in beef tenderness is a problem for industry and can be difficult to overcome, especially for Bos taurus indicus cattle. The objective of this study was to determine the association between calpastatin (CAST) polymorphisms (Single Nucleotide Polymorphism, SNP) and tenderness in beef of Nellore cattle with divergent temperaments. The animals were genotyped, their temperaments were evaluated, and contrasting groups were formed based on these combined factors (n = 21; calm = 10, 5 AA and 5 AG; and excitable = 11, 4 AA and 7 AG). Carcass pH and temperature decline were monitored (24 h), beef color was measured, and tenderization was assessed by shear force and myofibrillar fragmentation index (MFI) during beef aging (28 d). Calpastatin activity was also determined (24 h). Treatments of temperament and genotype as well as interactions were tested in a randomized block design in a factorial arrangement of 2 (temperament: calm and excitable) × 2 (genotypes: AA and AG). Calm animals harboring the AA allele in the CAST gene were associated with tender beef at 28 d. Excitable cattle or animals harboring the AG allele were associated with less tender beef; excitable AG showed greater calpastatin activity. Excitable animals produced beef with a slower tenderization process and less extension.

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.

The calpain system is the central player for meat tenderization and the calpastatin activity plays an important role in beef tenderness of Bos taurus indicus cattle. This study investigated whether dietary vitamin D3 induced gene expression of μ-calpain (CAPN1), total calpastatin (CAST T), and their variants (CAST I and II). Animals received none or 2 × 106 IU of vitamin D3 for either 2 or 8 days before slaughter and were submitted to different conditions during feedlot: sun exposure or artificial shade. Steaks from Longissimus lumborum were fabricated, aged for 1, 7, and 21 days post-mortem, and later used for the analyses of shear force and the myofibrillar fragmentation index. Vitamin D3 did not influence mRNA abundance; however, it induced a greater CAST II transcript in animals supplemented 8 days before slaughter. There was a negative association between CAST II abundance and the shear force, which revealed an important modulation of the calpain system expression due to vitamin D supplementation. This result is an important tool for strategies to improve beef tenderness.

Muscle properties and metabolism influence muscle to meat conversion. Fiber type profile impacts glycolytic capacity as well as protein turnover rate in vivo. Our objective was to investigate protease content and activation during the early postmortem period using muscles with known divergent metabolism. Samples from longissimus lumborum (LL) and diaphragm (Dia) were taken from predominantly Angus steer carcasses (n = 6) at 1, 3, and 24 h postmortem and frozen. Myosin heavy chain (MyHC) isoforms, ATP, glycogen, glucose, glucose-6-phosphate (G6P), and lactate concentrations were determined. Procaspase-3, calpain-1, calpastatin, desmin, and troponin-T were assessed by immunodetection. Muscles showed contrasting MyHC profiles, with LL represented primarily by IIx and IIa isoforms (∼88%) whereas Dia contained mostly (80%) type I isoform. Glycogen degradation was more pronounced in LL and coincided with more rapid accumulation of glucose and lactate (P < 0.01). Procaspase-3 content was influenced by muscle (m: P < 0.01), being greater in Dia. Fragments indicating activation of procaspase-3 postmortem were not detected. Calpain-1 autolysis and intact calpastatin (135 kDa) content were influenced by muscle and time (m × t: P < 0.01 and P < 0.01, respectively). Calpastatin fragmentation postmortem was not associated with greater procaspase-3 content. In conclusion, fast glycolytic LL displayed faster protease activation and greater proteolysis during the first 24 h postmortem.

Meat quality is traditionally associated with anaerobic metabolism due to cessation of the oxygen supply post-mortem. However, mitochondrial (mt) function early postmortem may affect the development of meat quality characteristics, such as adenosine triphosphate levels and pH decline. Therefore, the objective of this study was to evaluate mt function ex vivo during the first 24 h postmortem in muscles with differences in mt content. Samples from longissimus lumborum (LL) and diaphragm (Dia) were taken from steers (n = 6) at 1, 3, and 24 h postmortem and frozen to determine citrate synthase (CS) activity and mt protein expression (immunodetection) or were fresh-preserved for high-resolution respirometry. Integrative oxygen consumption rate (picomoles per second per milligram of tissue) was measured and normalized to CS activity as a proxy for mt content (intrinsic mt function, picomoles per second per unit CS). CS activity (P < 0.001) and mt protein expression (P < 0.001) were greater in Dia, which was reflected in mt respiration. Muscle type affected (P < 0.001) integrative leak respiration and was greater in mt from Dia; oxidative phosphorylation (OXPHOS) was also greater in Dia and influenced by time postmortem (muscle × time: P = 0.01). Intrinsic leak and OXPHOS were affected by muscle and time (muscle × time: P = 0.05 and P = 0.01, respectively), with the most pronounced differences at 24 h postmortem. Stimulation of OXPHOS by cytochrome c as an indicator of outer mt membrane integrity was influenced by muscle and time postmortem (muscle × time: P = 0.03); it was greater in mt from LL. Despite intrinsic differences in respiratory function at 24 h, mt from both muscles were intact and coupled at 1 h postmortem. Reduced content and respiratory function in mt from LL are associated with early fragmentation, which could impact protease activation and subsequently meat quality.

Functional properties and integrity of skeletal muscle mitochondria (mt) during the early postmortem period may influence energy metabolism and pH decline, thereby impacting meat quality development. Angus typically produce more tender beef than Brahman, a Bos indicus breed known for heat tolerance. Thus, our objectives were to compare mt respiratory function in muscle collected early postmortem (1 h) from Angus and Brahman steers (n = 26); and to evaluate the effect of normal and elevated temperature on mt function ex vivo. We measured mt oxygen consumption rate (OCR) in fresh-permeabilized muscle fibers from Longissimus lumborum (LL) at 2 temperatures (38.5 and 40.0 °C) and determined citrate synthase (CS) activity and expression of several mt proteins. The main effects of breed, temperature, and their interaction were tested for mt respiration, and breed effect was tested for CS activity and protein expression. Breed, but not temperature (P > 0.40), influenced mt OCR (per tissue weight), with Brahman exhibiting greater complex I+II-mediated oxidative phosphorylation capacity (P = 0.05). Complex I- and complex II-mediated OCR also tended to be greater in Brahman (P = 0.07 and P = 0.09, respectively). Activity of CS was higher in LL from Brahman compared to Angus (P = 0.05). Expression of specific mt proteins did not differ between breeds, except for higher expression of adenosine triphosphate (ATP) synthase subunit 5 alpha in Brahman muscle (P = 0.04). Coupling control ratio differed between breeds (P = 0.05), revealing greater coupling between oxygen consumption and phosphorylation in Brahman. Our data demonstrate that both Angus and Brahman mt retained functional capacity and integrity 1-h postmortem; greater oxidative phosphorylation capacity and coupling in Brahman mt could be related to heat tolerance and impact early postmortem metabolism.