This study evaluated the effects of shade removal, shade provision, and shade plus chromium (Cr) propionate supplementation on growth performance, metabolic responses, thermotolerance, and carcass characteristics of Bos indicus-influenced finishing steers exposed to hot and humid conditions. Twenty-four steers [body weight (BW) = 464 ± 15 kg] were assigned to one of three treatments for an 80-d experimental period: (1) control (no shade, and no Cr supplementation, CON), (2) shade and no Cr supplementation (S), or (3) shade + Cr supplementation (0.5 mg Cr/kg DM, SCr). Treatment × day interactions (P ≤ 0.05) were observed for BW, DMI, ADG, glucose, NEFA, and cortisol. The SCr steers had greater BW on d 28, 42, 70, and 80 and DMI from 0 to 42 compared to that of S steers. Serum glucose concentrations were lower (P = 0.01) in SCr steers on d 56 and 70, and serum cortisol concentrations were reduced (P < 0.01) on d 14 and tended (P = 0.10) to remain lower throughout the experimental period. Shade reduced (P < 0.01) respiration rate and rectal temperature during peak afternoon heat load. Shade plus chromium supplementation increased (P ≤ 0.05) hot carcass weight and backfat thickness, with no effects (P ≥ 0.20) on dressing percentage, longissimus muscle area, or marbling score. These results indicate that shade improved thermotolerance, whereas steers receiving shade plus Cr supplementation exhibited improved growth performance and carcass traits under hot and humid conditions.

Smaller carcasses are routinely subjected to the same chilling protocols, potentially altering postmortem temperature decline and the metabolic processes that regulate pH decline and lean color development, perhaps predisposing them to quality defects such as atypical dark-cutting (ATDC). Because previous ATDC research has largely relied on limited sampling time points, interactions between chilling rate and early postmortem metabolism may be overlooked. Therefore, this study evaluated whether carcass weight-dependent differences in chilling rate alter early postmortem metabolism and contribute to darker lean color development associated with ATDC. Forty-four beef carcass sides were classified as heavy weight (HW; 231.4 ± 2.1 kg) or light weight (LW; 181.1 ± 2.1 kg). Longissimus lumborum temperature, pH, and metabolites were assessed from 0 to 24 h postmortem, as well as protein abundance, color, and tenderness were evaluated. Light-weight carcasses chilled more rapidly than HW carcasses, resulting in an approximately 3 °C lower muscle temperature between 3 and 24 h postmortem (P < 0.05). This accelerated chilling coincided with darker lean color, evidenced by lower L* values (P < 0.05). While ultimate pH did not differ between groups, LW carcasses retained greater glycogen and glucose-6-phosphate concentrations early postmortem despite similar initial substrate availability. Additionally, LW carcasses exhibited greater shear force at 1 d postmortem (P < 0.05) but tenderness differences resolved with aging. These findings demonstrate that relatively modest differences in carcass weight (∼ 50 kg/side) can alter chilling rate thus altering early postmortem metabolic progression and provide one potential mechanistic explanation for the development of ATDC-like phenotypes.

This study investigated dietary vitamin E (VE) as a targeted in vivo fortification strategy to proactively protect calf muscle against post-slaughter, salt-induced deterioration. Supranutritional VE supplementation is well known to elevate tocopherol levels in plasma and muscle, thereby enhancing antioxidant capacity. Baseline assessments of commercial beef demonstrated that conventional salt treatments rapidly overwhelm this system, promoting extensive meat deterioration. To overcome this, two sequential experiments were conducted on male calves to optimize a pre-slaughter VE supplementation protocol aimed at enhancing oxidative stability in meat. Experiment 1 compared three α-tocopherol acetate concentrations to determine the most effective over 60 days: control (1.1 g/d; n = 6), medium-dose (2.2 g/d; n = 4), or high-dose (4.4 g/d; n = 6). High-dose feeding maximized muscle VE accumulation (P = 0.0146), minimized salt-induced lipid peroxidation (P = 0.0082), and preserved redness (a* values; P = 0.0207). To maximize practical and economic viability by determining the minimum effective duration, Experiment 2 evaluated a high-dose regimen (3.7 g/d) for 10, 25, or 40 days (n = 5 per time point) against a control (0.35 g/d; n = 5). Forty-day supplementation achieved superior salted muscle VE (P = 0.0037, Cohen's d = 5.05), neutralized lipid peroxidation (P = 0.0005, Cohen's d = 6.05), and provided biologically meaningful pigment preservation (Cohen's d = 0.78).We conclude that a standardized 40-day, high-dose VE feeding protocol effectively fortifies calf muscle tissue in vivo before harvest, providing a robust physiological defense against post-slaughter salt processing to ensure superior oxidative stability.

Plane of nutrition influences animal growth rate and muscle fiber composition, potentially through altering skeletal muscle metabolism. The objective of this study was to evaluate changes in skeletal muscle metabolism in response to altering diet without changes in growth rate. To that end, cattle were fed high-concentrate diets typically used in commercial feedlots until they reached market weight, approximately 604 kg. Cattle were then placed on isocaloric, maintenance diets consisting of primarily grain and forage diets for 60 d until harvest. Cattle fed a forage-based maintenance diet had increased mitochondrial succinate dehydrogenase (SDHA, P <  0.05), citrate synthase (CS, P <  0.01), electron transport chain complex I (CI, P <  0.01), complex II (CII, P <  0.01), and voltage dependent anion channel (VDAC, P <  0.001) protein abundances. Mitochondrial oxygen consumption rate was greatest in muscle mitochondria of forage-fed cattle when provided glutamate/malate (P <  0.05), acetoacetate/malate (P <  0.01), and palmitoyl-carnitine/malate (P <  0.05). This increased function is partially explained by increases in the abundance of electron transport chain complexes and the voltage-gated dependent anion channel (VDAC, P <  0.01), the pore allowing ATP to leave the mitochondria. Significant interaction between diet and muscle were noted for ACSS1 (P <  0.01) gene expressions. Additionally, forage-maintained cattle had increased ACSS1 (P <  0.01), CPT1b (P <  0.05), and CPT2 (P <  0.05) gene expression when compared to grain-maintained cattle. These data suggest part of the mechanism responsible for altered mitochondrial function in response to altered substrate availability may lie in the regulation of ACSS1, CPT1b, and CPT2 gene expressions for acetate and fatty acid metabolism. Together, diet influences muscle acetate and fatty acid gene expressions, mitochondrial protein abundances, and mitochondrial function in fatty acid substrate oxidation, highlighting the role of nutrition on skeletal muscle metabolism and possibly as a means of regulating tissue growth.

Rising global temperatures challenge poultry production by disrupting the cecal microbiota, which is essential for chicken health. Thermal manipulation (TM) during embryogenesis is a potential strategy to enhance thermotolerance in broilers. This study examined TM’s effects on the cecal microbiome, body weight (BW), and body temperature (BT) under chronic heat stress (CHS). Fertile Indian River eggs (n = 800) were incubated under control (37.8 °C, 56% RH) or TM conditions (39 °C, 65% RH for 18 h per day from embryonic day 10 to 18). On post-hatch day 18, male chicks were assigned to either CHS (35 ± 0.5 °C for five days) or thermoneutral conditions (24 ± 0.5 °C). The CHS-TM group showed a significantly higher BW than the CHS-CON group (p < 0.05). Under thermoneutral conditions, TM chicks had a lower BT on day 1 (p < 0.05), while the CHS-TM group exhibited a non-significant BT reduction compared to the CHS-CON group under heat stress (p > 0.05). An analysis of the gut microbiome showed that the beta diversity analysis (PERMANOVA, p < 0.05) indicated distinct microbial shifts. Firmicutes and Bacteroidota dominated the phylum level, with CHS increased Bacilli and Lactobacillus while reducing Lachnospirales in the CHS-TM group. These findings suggest that TM modulates gut microbiota and mitigates BW loss, offering a potential strategy to enhance broilers’ resilience to heat stress.

The aim of this study was to explore the effects of growth rate and finishing system (feedlot or pasture) on postmortem muscle metabolism and subsequent beef color development. Seventy-two Angus × Nellore crossbred steers were randomly assigned to one of four treatment combinations: 1) feedlot, high growth rate (FH); 2) feedlot, low growth rate (FL); 3) pasture, high growth rate (PH) and 4) pasture, low growth rate (PL). Animals were harvested either at a constant body weight (BW; 530 kg) or days on feed (DOF; 140 d). PL cattle had darker (P < 0.001) lean, slower (P = 0.006) pH declines and greater (P = 0.005) ultimate (24 h) pH values, as well as lower glycolytic potentials (P = 0.019) in the Longissimus muscle compared to FH cattle when harvested based on DOF. Muscle from PH had similar muscle energy metabolism when subjected to an in vitro glycolysis system, and beef color attributes compared to those of FL cattle. Growth rate influenced postmortem beef metabolism and color attributes more notably when harvested at a constant BW endpoint compared to those harvested on a constant DOF. Both feeding regime and growth rate affected meat quality characteristics. These results demonstrate that feeding strategies should be carefully considered when attempting to optimize beef quality development, especially fresh color.

An in vitro assay was developed to study protease activity during the maturation of beef postmortem. Myofibrils were purified from the semitendinosus and used as a sentinel for assessing the activity of endogenous proteases in longissimus thoracis et lumborum (LTL) and the extensor carpi radialis (ER) over time postmortem in beef carcasses. Samples were collected from each muscle at 0, 1, 2, 7, and 14 d of aging and snap frozen. Samples were powdered and added to an in vitro proteolysis assay containing buffer and purified myofibrils. Aliquots were collected at 0, 2, 120, 480, and 1440 min of incubation, and intact desmin and troponin-T were quantified. Digestions at 0 and 1 d using either muscle had little desmin degradation during the entire digestion period. In contrast, LTL muscle collected at 2, 7, and 14 d had the greatest proteolytic capacity as indicated by disappearance of intact desmin by 480 and 1440 min incubation. Though degradation ensued using powdered ER muscle, disappearance of intact proteins was limited. Degradation in vitro paralleled that observed in intact muscle. Addition of ethylene glycol tetra-acetic acid (EGTA), a cysteine protease inhibitor, and calpastatin inhibited proteolysis and suggest proteolytic activity observed in muscles and detected in our proteolysis assays is due to an active calpain protease. Collectively, our data show an active protease is minimal in bovine muscle until 48 h postmortem in the LTL muscle and suggest an in vitro assay containing purified myofibrils is a potential tool for studying temporal changes in proteolysis during the maturation and tenderization of beef across muscles.

Thermal manipulation (TM) during embryogenesis is a promising non-pharmacological strategy to enhance physiological resilience in broiler chickens. This study evaluated the impact of thermal conditioning of fertile eggs on growth performance, inflammatory responses, and molecular stress markers following a post-hatch lipopolysaccharide (LPS) challenge. Fertilized eggs (average weight 62 ± 3 g) were obtained from 35-week-old Indian River broiler breeder hens. A total of 720 eggs were randomly assigned to either the control group (n = 360) or the TM group (n = 360), with each group consisting of two replicates of 180 eggs. Control eggs were maintained under standard incubation conditions (37.8 °C, 56% RH), while TM eggs were subjected to elevated temperature (38.8 °C, 65% RH) for 18 h daily from embryonic day 10 to 18. On post-hatch day 15, control and TM groups were administered either saline or LPS via intraperitoneal (IP) injection. Body weight and temperature, internal organ weights, and splenic mRNA expression levels of inflammatory cytokines, toll-like receptors, transcription factors, and heat shock proteins were assessed. TM did not alter hatchability (p = 0.633), but significantly shortened hatch time (p < 0.05) and improved feed efficiency (p < 0.05). While LPS induced marked inflammatory responses in all birds, those subjected to TM exhibited attenuated proinflammatory cytokine expression, enhanced anti-inflammatory signaling, and differential regulation of stress-associated genes, including nuclear factor kappa B (NF-κB), heat shock protein 70 (HSP70), and heat shock factors (HSFs). These findings suggest that TM during incubation promotes a more regulated immune response and improved stress adaptation post-hatch. This approach offers a potential antibiotic-free intervention to enhance broiler health, performance, and resilience under immunological stress.

Thermal manipulation (TM) during embryogenesis has emerged as a promising strategy to enhance post-hatch performance and improve resilience to environmental and bacterial stress, which offers a potential alternative to reduce the reliance on antibiotic growth promoters (AGPs) in broiler production. This study investigated TM’s ability to modulate broilers’ cecal microbiota and enhance resilience to lipopolysaccharide (LPS)-induced stress. Eggs in the control group (CON) were incubated at 37.8 °C and 56% relative humidity (RH), while TM eggs were exposed to 39 °C and 65% RH for 18 h daily from embryonic days 10–18. Post-hatch, the LPS subgroups (LPS-CON, LPS-TM) received intraperitoneal LPS injections, and body weight (BW) and temperature (BT) were monitored. Cecal samples were collected for microbiome sequencing. Alpha diversity showed no differences (p > 0.05), but beta diversity revealed differences between groups (PERMANOVA, p < 0.05). Firmicutes and Bacteroidota dominated the microbiota at the phylum level. Oscillospirales were enriched in the TM groups (p < 0.001) and Lactobacillales were increased in the LPS-CON group (p < 0.019). LPS reduced BT in the CON group (p < 0.01), but LPS-TM birds bypassed hypothermia. LPS significantly reduced BW (p < 0.001), while TM had no significant effect. These findings demonstrate TM’s enduring influence on gut microbiota and stress resilience, highlighting its potential to reduce antibiotic reliance and mitigate antimicrobial resistance (AMR) in poultry production.

During skeletal muscle growth, metabolic processes regulating muscle tissue exhibit remarkable adaptability. The objective of this study was to determine the involvement of mitochondria function in the shift of metabolism in porcine skeletal muscle. To alter metabolism, we utilized β-adrenergic agonists (BAA) supplementation known to increase the proportion of fast-twitch fibers. To assess the role of the mitochondria in this process, we utilized a naturally occurring mutation in domestic pigs containing a constitutively active adenosine monophosphate activated protein kinase (AMPKγ3R200Q) that results in greater tissue oxidative capacity. Mature pigs with or without AMPK mutation (control and AMPKγ3R200Q) were fed BAA (0 and 9 ppm) for 1 wk, then were euthanized and longissimus lumborum muscle samples were collected and mitochondria were isolated. Mitochondria from muscle of AMPKγ3R200Q pigs had higher (P < 0.05) oxygen consumption rates (OCR) than that of control pigs when using pyruvate/malate substrates under ADP-stimulated conditions. When provided succinate/rotenone substrates, an interaction (P < 0.05) was noted for basal respiration, where mitochondria from muscle of control pigs fed 0 ppm BAA had lower OCR compared to that of AMPKγ3R200Q pigs and that of those fed 9 ppm BAA. These data show that BAA have more pronounced effects on control pigs than AMPKγ3R200Q pigs which may be due to the inherently greater oxidative capacity of mutant pig muscle. After 1 wk of feeding BAA, there was an increase in β1-adrenergic receptor gene expression in pigs fed BAA (Treatment, P = 0.06; Interaction P = 0.08). Oxidative protein abundance increased for succinate dehydrogenase (P < 0.01) and citrate synthase (CS, P < 0.001) in AMPKγ3R200Q muscle. Additionally, CS activity in isolated mitochondria from muscle of AMPKγ3R200Q pigs was lower (P = 0.08), but whole muscle of AMPKγ3R200Q pigs had overall higher CS activity (P < 0.01). There were no differences in glycolytic enzyme protein abundances, however, there was increased lactate dehydrogenase (P < 0.001) activity in muscle of control pigs and that of muscle from pigs fed BAA (P < 0.05). Together, these data indicate that mitochondria function is altered in porcine skeletal muscle when pigs are supplemented with BAA and suggest part of the mechanism by which BAA supplementation augments muscle growth in pigs potentially lies within the regulation of β1-adrenergic receptors and changes in mitochondrial function.

Background: Mitochondria are considered the powerhouse of cells, and skeletal muscle cells are no exception. However, information regarding muscle mitochondria from different species is limited. Methods: Different muscles from cattle, pigs and chickens were analyzed for mitochondrial DNA (mtDNA), protein and oxygen consumption. Results: Bovine oxidative muscle mitochondria contain greater mtDNA (p < 0.05), protein (succinate dehydrogenase, SDHA, p < 0.01; citrate synthase, CS, p < 0.01; complex I, CI, p < 0.05), and oxygen consumption (p < 0.01) than their glycolytic counterpart. Likewise, porcine oxidative muscle contains greater mtDNA (p < 0.01), mitochondrial proteins (SDHA, p < 0.05; CS, p < 0.001; CI, p < 0.01) and oxidative phosphorylation capacity (OXPHOS, p < 0.05) in comparison to glycolytic muscle. However, avian oxidative skeletal muscle showed no differences in absolute mtDNA, SDHA, CI, complex II, lactate dehydrogenase, or glyceraldehyde 3 phosphate dehydrogenase compared to their glycolytic counterpart. Even so, avian mitochondria isolated from oxidative muscles had greater OXPHOS capacity (p < 0.05) than glycolytic muscle. Conclusions: These data show avian mitochondria function is independent of absolute mtDNA content and protein abundance, and argue that multiple levels of inquiry are warranted to determine the wholistic role of mitochondria in skeletal muscle.

This study examined the potential influence of mitochondrial calcium sequestering ability on calpain-1 autolysis and proteolysis in vitro. We first tested whether mitochondria can sequester calcium in an in vitro setting. Isolated bovine mitochondria (0, 0.5, or 2 mg/mL) were incubated in a buffer containing varying calcium levels (0, 50, or 100 μM). An inverse relationship between mitochondrial content and measured free calcium was observed (P < 0.05), confirming that mitochondria can sequester calcium within the concentration range tested. In the first in vitro experiment, intact mitochondria (0, 0.5, or 2 mg/mL) were incorporated into an in vitro model simulating postmortem muscle conditions, and calpain-1 autolysis and proteolysis were evaluated over a 168-h period. Adding intact mitochondria to the in vitro model decreased calpain-1 autolysis and proteolysis during the first 4 h of incubation (P < 0.05), likely through reducing calcium availability. However, accentuated calpain-1 autolysis and proteolysis were observed at 24 h. To further explore these effects, mitochondrial integrity was evaluated at varying pH and calcium levels. Mitochondrial integrity decreased as pH declined (P < 0.05), especially in the presence of calcium. Based on these results, we conducted a second in vitro experiment involving disrupted mitochondria. Unlike intact mitochondria, which exerted a suppressive effect on calpain-1 autolysis and proteolysis early on, disrupted mitochondria increased both parameters at most time points (P < 0.05). Overall, it appears that intact mitochondria initially cause a delay in calpain-1 autolysis and proteolysis, but as their integrity diminishes, both processes are enhanced.

Beef consumption is expected to increase worldwide, which necessitates the use of Bos indicus cattle that are well-adapted to harsher climates, like the tropics. Yet, beef from these cattle is considered inferior to that of Bos taurus breeds, primarily due to lowered tenderness values and reduced intramuscular fat content. However, the benefits of using Bos indicus genetics are numerous and undeniable. Herein, we explore how decreases in meat quality in these cattle may be offset by increases in livability. Further, we review the knowledge surrounding beef tenderness and explore the processes occurring during the early events of the transformation of muscle to meat that are different in this biological type and may be altered by stress. Growth rate, calpastatin activity and mitochondrial function will be discussed as they relate to tenderness. The opportunities of using Bos indicus cattle are of great interest to the beef industry worldwide, especially given the pressures for enhancing the overall sustainability and carbon footprint of this sector. Delivering a consistently high-quality product for consumers by exploiting Bos indicus genetics in a more sustainable manner will be proposed. Information on novel factors that influence the conversion of muscle to meat is explored to provide insights into opportunities for maximizing beef tenderization and maturation across all cattle. Exploring the use of Bos indicus cattle in modern production schemes, while addressing the mechanisms undergirding meat tenderness should provide the industry with a path forward for building greater demand through producing higher quality beef.

In March 2020, the World Health Organization declared COVID-19 a pandemic, which ultimately led to many meat processors temporarily shutting down or reducing processing capacity. This backlog in processing capacity forced many feedlots to retain cattle for longer periods of time and assume the risk of major market fluctuations. The aim of this study was to understand how a dietary insult affects meat quality and muscle metabolism in market-ready steers (590 kg). Sixteen market-ready (590 kg) commercial Angus crossbred steers were subjected to a maintenance diet of either forage or grain for 60 d. Longissimus lumborum (LL) muscle samples were collected immediately postmortem and processed for characteristics reflecting the underlying muscle fiber type and energy state of the tissue. Despite cattle being subjected to a 60-d feeding period, there were no detectable differences (P > 0.05) in carcass characteristics, color of lean, or ultimate pH (pH(u)). Moreover, our data show that muscle plasticity is rather resilient, as reflected by lack of significance (P > 0.05) in oxidative and glycolytic enzymes, myosin heavy chain isoforms (MyHC), myoglobin, and mitochondrial DNA (mtDNA) contents. These data show that market-ready steers are capable of withstanding a low-input feeding strategy up to 60 d without dramatically impacting underlying muscle characteristics and meat quality development.

This research aimed to explore the potential influence of mitochondria on the rate of anaerobic glycolysis. We hypothesized that mitochondria could reduce the rate of anaerobic glycolysis and pH decline by metabolizing a portion of glycolytic pyruvate. We utilized an in vitro model and incorporated CPI-613 and Avidin to inhibit pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC), respectively. Four treatments were tested: 400 mu M CPI-613, 1.5 U/ml Avidin, 400 mu M CPI-613 + 1.5 U/ml Avidin, or control. Glycolytic metabolites and pH of the in vitro model were evaluated throughout a 1440-min incubation period. CPI-613-containing treatments, with or without Avidin, decreased pH levels and increased glycogen degradation and lactate accumulation compared to the control and Avidin treatments (P < 0.05), indicating increased glycolytic flux. In a different experiment, two treatments, 400 mu M CPI-613 or control, were employed to track the fates of pyruvate using [C-13(6)]glucose. CPI-613 reduced the contribution of glucose carbon to tricarboxylic acid cycle intermediates compared to control (P < 0.05). To test whether the acceleration of acidification in reactions containing CPI-613 was due to an increase in the activity of key enzymes of glycogenolysis and glycolysis, we evaluated the activities of glycogen phosphorylase, phosphofructokinase, and pyruvate kinase in the presence or absence of 400 mu M CPI-613. The CPI-613 treatment did not elicit an alteration in the activity of these three enzymes. These findings indicate that inhibiting PDH increases the rate of anaerobic glycolysis and pH decline, suggesting that mitochondria are potential regulators of postmortem metabolism.

Since veal production has declined in the U.S., American veal producers are currently making efforts to implement new production standards to improve product quality and animal welfare. In this study, we hypothesized that diets containing brewery grains, starch and omega-3 fatty acids could lower a blood stress indicator and improve meat quality, mostly from a nutritional value stand point. Holstein bull calves with approximately 94.67 ± 12.07 kg of body weight and two months old were randomly assigned to 1 of 3 dietary treatments. Diets were formulated with nonmedicated milk replacer, microbreweries spent grains, and a mineral mix (CONTROL); CONTROL + isolated maize starch (STARCH); and CONTROL +3% fish oil (OMEGA-3). Veal calves fed all three diets were heavier than calves of the same age from experiments reported in the existing literature. Dietary treatments did not affect carcass weights, pH, color, moisture, sensory attributes, volatile profile, and fat quality indexes. Calves fed STARCH and OMEGA-3 showed the lowest levels of blood cortisol. Veal fed CONTROL and OMEGA-3 had higher concentrations of ΣMUFA when compared with STARCH. Veal fed OMEGA-3 had the highest concentrations of EPA, DHA, and Σn-3. Veal from all treatments had very high concentrations of ΣMUFA, mostly driven by high levels of c-9 18:1 n-9 from the milk replacer. Feeding OMEGA-3 lowered blood cortisol and increased levels of EPA and DHA without harming sensory attributes. Overall, including brewery grains, starch and fish oil in liquid diets containing milk replacer can improve veal production.

Grass-fed beef is becoming increasingly popular. However, grass-fed beef tends to be darker in color compared to its grain-fed counterparts. Because consumers prefer bright-cherry red beef, the disparity in grass-fed beef color limits marketing options. Therefore, the aim of this study was to determine whether dry aging impacts the dark color of grass-fed beef. This study found dry-aging improved lean color of grass-fed beef, making it comparable to grain-fed beef in just 14 d. This enhanced color proved stable through 21 d of aging. These data argue that grass-fed beef, though initially darker than of grain-fed cattle, if managed accordingly postmortem can reach similar lean color endpoints to that of grain-fed beef.

During phases of skeletal muscle growth, the metabolic processes regulating muscle tissue exhibit remarkable adaptability. This metabolic flexibility is an essential component of maintaining the health and functionality of skeletal muscle, which allows the capacity to transition between oxidative and glycolytic metabolic pathways. Within the occurrence of these metabolic shifts, the exact underlying mechanisms that orchestrate these transitions within the context of mitochondrial function remain unresolved. Therefore, our objective is to determine the role of mitochondria during a shift in metabolism, through measuring functional capacity, gene expression, and protein abundance. To investigate this shift, we utilized β-adrenergic agonists (BAA) supplementation, due to its ability to increase the proportion of fast-twitch fibers in skeletal muscle. To assess the role of the mitochondria, we utilized a mutated pig, containing a constitutively active adenosine monophosphate activated protein kinase (AMPKγ3R200Q) that contains a greater oxidative capacity in a habitually glycolytic skeletal muscle. In this current study, mature pigs (wildtype and AMPKγ3R200Q) were fed BAA (0 and 9ppm) for 1 week, then euthanized and longissimus dorsi muscle samples were collected. Mitochondria of AMPK mutated pigs had a higher ( P = 0.08) oxygen consumption rate with pyruvate/malate substrates when stimulated with ADP when compared to their wildtype (WT) counterpart. When given succinate/rotenone substrates, there was an interaction ( P = 0.04) noted for basal respiration, where WT pigs fed control diets had lower oxygen consumption compared to that of AMPK mutated pigs and those fed BAA. These data suggest that BAA has more of an effect on WT pigs than AMPK mutated pigs, possibly due to the inherent increased oxidative metabolism in mutant pigs. In addition, skeletal muscle mitochondria of AMPK mutated pigs had higher ( P = 0.04) maximal respiration compared to that of their WT counterpart. After 1 week of feeding BAA, there were no differences in mitochondrial DNA content, but there was an increase in β1-adrenergic receptor gene expression in pigs fed BAA (Diet, P = 0.06; Interaction P = 0.08). Oxidative protein abundance increased for succinate dehydrogenase ( P < 0.01) and citrate synthase ( P = 0.08) in the skeletal muscle of AMPK mutated pigs. Glycolytic proteins were increased for lactate dehydrogenase ( P < 0.05) and glyceraldehyde 3-phosphate dehydrogenase ( P < 0.01) in the muscle of WT pigs. No interactions between genotype and diet on the protein abundance level was noted. Together, these data show that mitochondria function is altered in porcine skeletal muscle when pigs are supplemented with 1 week of BAA; however, it is not detected in protein levels after 1 week. These data suggest part of the mechanism by which BAA supplementation augments muscle growth in pigs lies within the regulation of β1-adrenergic receptors and changes in mitochondrial function. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A key player in energy metabolism is phosphofructokinase-1 (PFK1) whose activity and behavior strongly influence glycolysis and thus have implications in many areas. In this research, PFK1 assays were performed to convert F6P and ATP into F-1,6-P and ADP for varied pH and ATP concentrations. PFK1 activity was assessed by evaluating F-1,6-P generation velocity in two ways: (1) directly calculating the time slope from the first two or more datapoints of measured product concentration (the initial-velocity method), and (2) by fitting all the datapoints with a differential equation explicitly representing the effects of ATP and pH (the modeling method). Similar general trends of inhibition were shown by both methods, but the former gives only a qualitative picture while the modeling method yields the degree of inhibition because the model can separate the two simultaneous roles of ATP as both a substrate of reaction and an inhibitor of PFK1. Analysis based on the model suggests that the ATP affinity is much greater to the PFK1 catalytic site than to the inhibitory site, but the inhibited ATP-PFK1-ATP complex is much slower than the uninhibited PFK1-ATP complex in product generation, leading to reduced overall reaction velocity when ATP concentration increases. The initial-velocity method is simple and useful for general observation of enzyme activity while the modeling method has advantages in quantifying the inhibition effects and providing insights into the process.

Non-alcoholic fatty liver disease (NAFLD) is a range of disorders characterized by lipid accumulation in hepatocytes. Although this spectrum of disorders is associated with adult obesity, recent evidence suggests that this condition could also occur independently of obesity, even in children. Previously, we reported that pigs fed a formula containing medium-chain fatty acids (MCFAs) developed hepatic steatosis and weighed less than those fed an isocaloric formula containing long-chain fatty acids (LCFAs). Our objective was to determine the association between NAFLD and the skeletal muscle transcriptome in response to energy and lipid intake. Neonatal pigs were fed one of three formulas: a control formula (CONT, n = 6) or one of two isocaloric high-energy formulas containing either long (LCFA, n = 6) or medium (MCFA, n = 6) chain fatty acids. Pigs were fed for 22 d, and tissues were collected. Body weight at 20 and 22 d was greater for LCFA-fed pigs than their CONT or MCFA counterparts (p < 0.005). Longissimus dorsi weight was greater for LCFA compared with MCFA, while CONT was intermediate (p < 0.05). Lean gain and protein deposition were greater for LCFA than for CONT and MCFA groups (p < 0.01). Transcriptomic analysis revealed 36 differentially expressed genes (DEGs) between MCFA and LCFA, 53 DEGs between MCFA and CONT, and 52 DEGs between LCFA and CONT (FDR < 0.2). Feeding formula high in MCFAs resulted in lower body and muscle weights. Transcriptomics data suggest that the reduction in growth was associated with a disruption in cholesterol metabolism in skeletal muscles.