VTechWorks Repository :: Browsing by Author "Gerrard, David E."

Browsing by Author "Gerrard, David E."

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Acute and chronic heat stress alters the metabolic profile of skeletal muscle in growing swine
Won, Samantha Gwai Lan (Virginia Tech, 2012-08-02)
Heat stress (HS) causes significant losses to the U.S. swine industry in several production and health areas including efficient lean tissue accretion. Perturbations in skeletal muscle metabolism may participate in this defect. The study objectives were to examine the cellular bioenergetic profile in skeletal muscle of piglets subjected to thermal stress in utero and/or during postnatal life. To accomplish this, 96 offspring from 14 sows were prenatally exposed to 1 of 4 environmental treatments involving thermal neutral (TN, 25°C) or HS conditions (cyclical 28-34°C). Sows exposed to TN or HS throughout gestation are denoted TNTN and HSHS, respectively whereas sows heat-stressed for the first or second half of gestation are denoted HSTN and TNHS, respectively. At 14 weeks of age, offspring were exposed to one of two postnatal thermal environments, constant TN (21°C) or HS (35°C) for 24 hrs (acute study) or 5 weeks (chronic study). Pigs were sacrificed after treatment and longissimus dorsi skeletal muscle samples collected for molecular analyses. Differences (p<0.05) were observed in protein abundance of p-4eBP1 and total Rs6 and gene expression of Cox5B, CytB, EEF2, HK2, MURF, ND1, PGC-1Î±, SDHA, and TFAM during the acute heat stress study. Differences (p<0.05) were observed in protein abundance of 4eBP1, total Akt, and p-Rs6 and gene expression of CytB, MURF, and PGC-1Î± during the chronic heat stress study. These data indicate that acute postnatal HS alters skeletal muscle metabolism, which may favor a reduction in mitochondrial respiration and protein synthesis potentially via the mTOR pathway.
AMP-activated protein kinase and muscle metabolism
Scheffler, Tracy L. (Virginia Tech, 2012-07-11)
AMP-activated protein kinase (AMPK) is a major regulator of skeletal muscle metabolism with relevance to agriculture and human health. During the conversion of muscle to meat, the rate and extent of postmortem metabolism and pH decline largely determine pork quality development. Pigs with the AMPKγ3 R200Q mutation generate pork with low ultimate pH (pHu); this is attributed to high glycogen content, and greater "potential" to produce lactate and H+. We hypothesized that decreasing muscle phosphocreatine and creatine would decrease ATP buffering capacity, resulting in earlier termination of glycolysis and pH decline. Dietary supplementation with the creatine analogue, β-GPA, decreased muscle total creatine but negatively affected performance. Another experiment was conducted using control or β-GPA diet and wild type and AMPKγ3R200Q pigs in a 2Ã 2 factorial design. The loss of muscle total creatine was important in maintenance of ATP levels in AMPKγ3R200Q muscle early postmortem. Moreover, elevated glycogen did not affect pHu, supporting that energetic modifications induced by feed restriction and β-GPA supplementation influence extent of pH decline. Next, we utilized a line of pigs selected for differences in pHu. Another AMPKγ3 mutation (V199I), which is associated with higher pHu and lower glycolytic potential, was prevalent. The 199II genotype increased pHu in castrated males only. The wild type VV genotype increased glycolytic potential, but neither glycolytic potential nor lactate predicted pHu. In humans, AMPK activation is at least partly responsible for the beneficial effects of exercise on glucose transport and increased oxidative capacity in skeletal muscle. An inverse relationship exists between skeletal muscle fiber cross-sectional area and oxidative capacity, which suggests muscle fibers hypertrophy at the expense of oxidative capacity. Therefore, we utilized pigs possessing mutations associated with increased oxidative capacity (AMP-activated protein kinase, AMPKγ3R200Q) or fiber hypertrophy (ryanodine receptor 1, RyR1R615C) to determine if these events occur in parallel. RyR1R615C increased muscle fiber size; AMPKγ3R200Q increased oxidative capacity, evidenced by enhanced enzyme activity, mitochondrial function, and expression of mitochondrial proteins. Thus, pigs with both AMPKγ3R200Q and RyR1R615C possess increased fiber size and oxidative capacity, suggesting hypertrophy and oxidative capacity can occur simultaneously in skeletal muscle.
Biochemical Basis of Fresh Ham Color Development
Stufft, Kristen Marie (Virginia Tech, 2015-09-14)
Commercial hams display variation in color uniformity across the cut surface, especially the semimembranosus (SM) muscle. This variation in fresh ham color, or two-toning, persists through further processing and contributes to production of a less desirable end product. In an attempt to understand the underlying source of this color variation, we evaluated the differences in muscle fiber-type composition and glycolytic metabolism in the SM muscle of fresh hams differing in color uniformity. Fifty-eight fresh SM muscles, ranging in color, were selected at 24 h postmortem and each partitioned into four distinct regions and three color classes based on color uniformity in the caudal region. The L* (lightness) values were greatest and a* (redness) values lowest in the most caudal portions of the muscle. The caudal portion also exhibited the lowest ultimate pH (P < 0.0001), lowest myoglobin (P < 0.05), greatest glycolytic potential (GP) (P < 0.0001) and the lowest myosin heavy chain type I isoform (P < 0.0001) abundance of all regions in 'normal' colored hams. After segregating based on L* values, the caudal region had identical pH, GP, LDH, and MyHC-I, despite significant differences in L* (P < 0.0001). These data show the most caudal aspects of the SM are indeed more prone to adverse postmortem metabolism and suggest that inherent differences in muscles of the ham may make some areas of the ham more vulnerable to temperature abuse during harvesting.
Branched-Chain Amino Acid Metabolism in the Neonatal Pig
Yonke, Joseph Allan (Virginia Tech, 2022-06-29)
Branched-chain amino acids (BCAA) are a group of essential amino acids consisting of leucine, isoleucine, and valine. Leucine, in particular, has signaling functions affecting protein and energy metabolism. Plasma leucine concentration is positively correlated with obesity and associated metabolic disorders. We set out to test the hypothesis that metabolic dysfunction from high fat diets precedes dysfunctional BCAA metabolism. First, BCAA were supplemented to neonatal pigs for 4 weeks to evaluate whether the anabolic signaling function of leucine could increase muscle growth when fed for a longer duration than in previous studies. Neither normal pigs nor low birth weight pigs, which have naturally impaired muscle growth, grew better in response to BCAA supplementation, despite low birth weight pigs expressing less of the leucine sensing protein Sestrin2 in skeletal muscle. Furthermore, high plasma BCAA concentrations caused by the experimental diets had no effect on adiposity, liver fat accumulation, or expression of genes related to fatty acid synthesis, mitochondrial biogenesis, or energy expenditure in the pigs' livers. Having produced strong evidence that long term BCAA supplementation neither improves lean growth nor causes abnormal fat metabolism, we then tested whether fat supplementation changes BCAA metabolism. Pigs were fed milk replacer formula with either low energy (Control), or high energy from long-chain fatty acids (LCFA) or medium-chain fatty acids (MCFA) for 22 days. Although high fat diets did not increase plasma BCAA concentrations, the MCFA diet in particular caused metabolic changes which could lead to fatty liver disease and decreased oxidative BCAA disposal. Expression of fatty acid synthesizing genes were increased in the livers of pigs fed MCFA formula compared to Control and LCFA formula. Oxidation of α-ketoisocaproic acid was decreased in liver homogenate of pigs fed MCFA and LCFA formulas compared to Control. Additionally, hepatic oxidation of α-ketoisovalerate was decreased, and plasma concentration of α-ketoisovalerate was consequently increased, in pigs fed MCFA formula compared to Control, with LCFA formula causing intermediate results. In future research, it would be valuable to feed high MCFA formula for a longer period of time to determine whether nonalcoholic fatty liver disease will develop, and whether plasma BCAA concentrations will increase due to decreased oxidation. Overall, these studies concluded that long term BCAA supplementation does not increase muscle growth in neonatal pigs, but there is also no indication that they cause obesity or dysfunctional fat metabolism. On the other hand, high fat diets cause impairments in BCAA catabolism which may precede elevated plasma BCAA concentrations.
Defining the role of mitochondria in fresh meat quality development
Matarneh, Sulaiman K. (Virginia Tech, 2017-07-12)
During postmortem metabolism, hydrogen ions accumulate in the muscle and gradually lower the pH from 7.2 to an ultimate pH near 5.6. The ultimate pH of meat is widely valued as an indicator of fresh meat quality as it directly affects the quality characteristics of color, texture, and water holding capacity. Therefore, our research was conducted to identify the processes responsible for determining ultimate pH. Pigs harboring the AMPKï¿½•3R200Q mutation produce meat with extremely low ultimate pH (pH ~ 5.3) that is detrimental to quality. This phenomenon is often attributed to a greater glycogen content in muscle from the mutant pigs compared to wild-type pigs. However, our research indicated that greater glycolytic flux in muscle from these pigs causes a lower ultimate pH rather than greater tissue glycogen deposition. On the other hand, however, AMPKï¿½•3R200Q pigs contain more mitochondria and retain greater oxidative capacity. Hence, we hypothesized that mitochondria may contribute to the lower ultimate pH in muscle of these pigs. To test our hypothesis, isolated mitochondria were incorporated into an in vitro system the mimics postmortem glycolysis. Mitochondria enhanced glycolytic flux and pH decline in the in vitro system similar to that of AMPKï¿½•3R200Q pigs. After a series of experiments, we found that the causative agent for enhanced glycolytic flux is a soluble mitochondrial protein. In other experiments, mitochondrial F1-ATPase was found to be responsible for the majority of this effect, principally through promoting greater ATP hydrolysis at lower pH values, thereby allowing for greater flux through glycolysis. These data suggest that variations in ultimate pH may be more thoroughly explained and predicted by the abundance of mitochondria. Broiler pectoralis major muscle, which is a highly glycolytic muscle, possesses high ultimate pH (pH ~ 5.9) compared to pork and beef. We postulated that rapid carcass chilling reduces the flux through glycolysis, thereby causing premature termination of postmortem metabolism. Yet, chilling was only partially responsible for the high ultimate pH of pectoralis major muscle. However, we showed that pectoralis major of broiler chicken exhibits lower phosphofructokinase-1 activity compared to porcine longissimus lumborum muscle, which limits the flux through glycolysis.
Determining muscle plasticity and meat quality development of low-input extended fed market-ready steers
Wicks, Jordan C.; Wivell, Alexis L.; Beline, Mariane; Zumbaugh, Morgan D.; Bodmer, Jocelyn S.; Yen, Con-Ning; Johnson-Schuster, Chantal; Wilson, Thomas B.; Greiner, Scott P.; Johnson, Sally E.; Shi, Tim H.; Silva, Saulo Luz; Gerrard, David E. (Oxford University Press, 2024-05-02)
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 (pHu). 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.
Determining the Underlying Factors of Fresh Ham Color Variation
Elgin, Jennifer May (Virginia Tech, 2019-07-10)
Consumers associate meat color with quality. In some cases, especially in fresh and cured hams, the surface of a ham, whole, boneless or sectioned and formed displays a color gradient, which is unsightly and generally is considered of lower quality and must be discounted or processed different where color is less critical to the ultimate value of the resulting product. This disparity in color uniformity across fresh and cured products is sometimes known as two-toning and is most often found in the semimembranosus (SM) and associated muscles of fresh hams and is exacerbated with curing. The underlying color of fresh meat may be a function of postmortem metabolism or the underlying characteristics of those muscles involved. Therefore, the objective of this study is to determine the changes in underlying muscle type and postmortem metabolism in those muscles responsible for fresh ham color variation. Semimembranosus (SM) muscles of 15 mixed bred pigs were collected at 30 min and 1440 min postmortem, and muscle color was determined and muscles were collected and snap frozen for various energy metabolism analyses. Differences in color (L*, a* and b*) were noted across the face of the muscle by zone and time (P < 0.0001) but no differences were detected in pH and lactate, glucose, glucose-6-phosphate, and glycogen metabolisms. Glycolytic potential was also measured on a lactate basis and showed no differences across zone (P = 0.0746) but increased over time (P < 0.006). Lactate and pH were plotted and showed a linear relationship linear relationship (R2 = 0.928337) at 30 min (P < 0.0001) and at 1440 min (R2 = 0.161412; P < 0.0015). Muscle type characteristics showed no difference between zones and time. Buffering capacity showed a significant difference at pH 6 (P < 0.0359) and with time across all pH measured (P < 0.0001). These data suggest inherent differences, such as location and function, in the semimembranosus muscle may be more critical in developing fresh color than aberrations in postmortem metabolism.
Dietary Fat and Sugar Induce Obesity and Impair Glucose Tolerance in Prepubertal Pigs
van Eyk, Gregory Ryan (Virginia Tech, 2012-04-30)
A pig model of childhood obesity was used to study the effects of dietary energy on body adiposity, and blood parameters associated with impaired glucose clearance. Prepubertal female pigs weaned at 21 d of age were fed control (CON), refined sugar (SUG), fat (FAT), and sugar-fat (SUGFAT) diets in a completely randomized arrangement for 16 wk. Calories from fat were 8.9% for CON, 5.6% for SUG, 35.5% for FAT and 32.3% for SUGFAT. Calories from sugar were 36.0% for SUG and 30.7% for SUGFAT. Adding fat, sugar or both to diets increased (P < 0.003) calorie intake. Percentage body fat was higher (P < 0.0001) in all treatments compared to CON, and in SUGFAT and FAT compared to SUG. Ultrasound back fat depth was positively correlated (r2 = 0.909; P < 0.001) with percentage body fat and negatively (r = 0.912; P-value ) with percentage body protein. Area under the curve (AUC) in response to oral glucose tolerance at 14 wk was higher (P < 0.03) in FAT (+14.6%) and SUGFAT (+25.5%) pigs compared to CON. Glucose AUC from sugar-fed pigs was not different (P = 0.2) from fat alone-fed pigs. Adding sugar, fat, or their combination to diets increased (P < 0.008) blood glucose and decreased (P < 0.0009) plasma insulin AUC. These data show that inclusion of fat and refined sugar in pig diets increases body adiposity and impairs glucose homeostasis and suggests that the composition of calories consumed may have different effects than simply consumption of excess of calories.
Dietary manipulation causes childhood obesity-like characteristics in pigs
Fisher, Kimberly Denise (Virginia Tech, 2011-12-01)
An animal model to study complications resulting from childhood obesity is lacking. Our objective was to develop a porcine model for studying mechanisms underlying diet-induced childhood obesity. Pre-pubertal female pigs, age 35 d, were fed a high-energy diet (HED; n = 12), containing tallow and refined sugars, or a control corn-based diet (n = 11) for 16 wk. Initially, HED pigs self-regulated energy intake similar to controls, but, by wk 5, consumed more (P < 0.001) energy per kg body weight. At wk 15 and 22, pigs were subjected to an oral glucose tolerance test (OGTT); blood glucose increased (P < 0.05) in control pigs and returned to baseline levels within 60 min. HED pigs were hyperglycemic at time 0, and blood glucose did not return to baseline (P = 0.01), even 3 h post-challenge. During OGTT, glucose area under the curve was higher and insulin area under the curve was lower in HED pigs compared to controls (P = 0.001). Pigs given 6 wk of dietary intervention, consuming a control diet, marginally improved glucose area under the curve and LDL-cholesterol although insulin area under the curve was unaffected. Chronic HED intake increased (P < 0.05) subcutaneous, intramuscular, and perirenal fat deposition, and induced hyperglycemia, hypoinsulinemia, and low-density lipoprotein hypercholesterolemia; however, a 6 wk dietary intervention partially recovered a normal physiology. These data suggest pre-pubertal pigs fed HED are a viable animal model for studying childhood obesity.
Driving an Oxidative Phenotype Protects Myh4 Null Mice From Myofiber Loss During Postnatal Growth
Zeng, Caiyun; Shi, Hao; Kirkpatrick, Laila T.; Ricome, Aymeric; Park, Sungkwon; Scheffler, Jason M.; Hannon, Kevin M.; Grant, Alan L.; Gerrard, David E. (Frontiers, 2022-02-24)
Postnatal muscle growth is accompanied by increases in fast fiber type compositions and hypertrophy, raising the possibility that a slow to fast transition may be partially requisite for increases in muscle mass. To test this hypothesis, we ablated the Myh4 gene, and thus myosin heavy chain IIB protein and corresponding fibers in mice, and examined its consequences on postnatal muscle growth. Wild-type and Myh4(-/-) mice had the same number of muscle fibers at 2 weeks postnatal. However, the gastrocnemius muscle lost up to 50% of its fibers between 2 and 4 weeks of age, though stabilizing thereafter. To compensate for the lack of functional IIB fibers, type I, IIA, and IIX(D) fibers increased in prevalence and size. To address whether slowing the slow-to-fast fiber transition process would rescue fiber loss in Myh4(-/-) mice, we stimulated the oxidative program in muscle of Myh4(-/-) mice either by overexpression of PGC-1 alpha, a well-established model for fast-to-slow fiber transition, or by feeding mice AICAR, a potent AMP kinase agonist. Forcing an oxidative metabolism in muscle only partially protected the gastrocnemius muscle from loss of fibers in Myh4(-/-) mice. To explore whether traditional means of stimulating muscle hypertrophy could overcome the muscling deficits in postnatal Myh4(-/-) mice, myostatin null mice were bred with Myh4(-/-) mice, or Myh4(-/-) mice were fed the growth promotant clenbuterol. Interestingly, both genetic and pharmacological stimulations had little impact on mice lacking a functional Myh4 gene suggesting that the existing muscle fibers have maximized its capacity to enlarge to compensate for the lack of its neighboring IIB fibers. Curiously, however, cell signaling events responsible for IIB fiber formation remained intact in the tissue. These findings further show disrupting the slow-to-fast transition of muscle fibers compromises muscle growth postnatally and suggest that type IIB myosin heavy chain expression and its corresponding fiber type may be necessary for fiber maintenance, transition and hypertrophy in mice. The fact that forcing muscle metabolism toward a more oxidative phenotype can partially compensates for the lack of an intact Myh4 gene provides new avenues for attenuating the loss of fast-twitch fibers in aged or diseased muscles.
Dual effects of obesity on satellite cells and muscle regeneration
Geiger, Ashley E.; Daughtry, Morgan R.; Yen, Con-Ning; Kirkpatrick, Laila T.; Shi, Hao; Gerrard, David E. (2020-08)
Obesity is a complex metabolic disorder that often leads to a decrease in insulin sensitivity, chronic inflammation, and overall decline in human health and well-being. In mouse skeletal muscle, obesity has been shown to impair muscle regeneration after injury; however, the mechanism underlying these changes has yet to be determined. To test whether there is a negative impact of obesity on satellite cell (SC) decisions and behaviors, we fed C57BL/6 mice normal chow (NC, control) or a high-fat diet (HFD) for 10 weeks and performed SC proliferation and differentiation assays in vitro. SCs from HFD mice formed colonies with smaller size (p < .001) compared to those from NC mice, and this decreased proliferation was confirmed (p < .05) by BrdU incorporation. Moreover, in vitro assays showed that HFD SCs exhibited diminished (p < .001) fusion capacity compared to NC SCs. In single fiber explants, a higher ratio of SCs experienced apoptotic events (p < .001) in HFD mice compared to that of NC-fed mice. In vivo lineage tracing using H2B-GFP mice showed that SCs from HFD treatment also cycled faster (p < .001) than their NC counterparts. In spite of all these autonomous cellular effects, obesity as triggered by high-fat feeding did not significantly impair muscle regeneration in vivo, as reflected by the comparable cross-sectional area (p > .05) of the regenerating fibers in HFD and NC muscles, suggesting that other factors may mitigate the negative impact of obesity on SCs properties.
Effect of Different Selection Criteria on Performance, Carcass and Meat Quality of Nellore Young Bulls
Silva, Juliana; Cônsolo, Nara Regina Brandão; Buarque, Vicente Luiz Macedo; Beline, Mariane; da Silva Martins, Taiane; Lobo, Annelise Aila Gomes; Gómez, Juan Fernando Morales; Eler, Joanir Pereira; Leme, Paulo Roberto; Netto, Arlindo Saran; Gerrard, David E.; Baldi, Fernando; Silva, Saulo Luz (MDPI, 2021-03-29)
This study was carried out to evaluate the effects of selection criteria for post-weaning daily gain (PWDG) and early sexual heifer precocity (PP14) on the performance, carcass traits and meat quality of Nellore bulls. In year one, 50 animals were selected according to their expected progeny differences (EPDs) for PWDG and grouped as high (HG) or low (LG) groups. In year two, 50 animals were selected according to EPD for PP14 and also grouped as high (HP) or low (LP). After slaughter, samples of the longissimus muscle area (LMA) were used to evaluate meat quality. Most of performance traits were not affected by the selection criteria. However, the HG group had higher dressing percentage (p = 0.028), LMA (p = 0.02) and fat trim in the forequarter (p = 0.04) compared to the LG group. The HP group tended to have greater dry matter intake (p = 0.08), LMA (p = 0.05), rump fat (p = 0.04), heavier striploins (p = 0.07), tenderloins (p = 0.09) and briskets (p = 0.08) compared with LP group. In conclusion, the selection based on divergent groups PWDG or PP14 has a small impact on performance, carcass and meat quality traits.
The Effect of Exercise on Lactating Sow Performance
Higgins, Erinn E. (Virginia Tech, 2011-06-23)
The objective of this study was to determine the effect of light, daily exercise on body condition score (BCS), soundness (SS), injury (IS), lesions (LS) weaning wt (WW), and back fat (BF) of lactating sows housed in farrowing crates. A total of 24 sows were used in four trials. Body weight (BW), BF, BCS, SS, IS, and LS were recorded at placement into the farrowing barn and again at weaning. A scale of 1 (poor) to 5 (excellent) was used for BCS, SS, and IS. Prior to farrowing, sows were grouped by BW and parity, and assigned to control (no exercise) or experimental (exercise) groups. After farrowing, the exercise sows (n=3) were removed from their crates for 1h/d for 17-19 d and encouraged to exercise; the control sows (n=3) remained in crates 24h/d. Saliva samples were collected 30 min prior to exercise and at 30 and 60 min after exercise for cortisol analysis. Piglets were weaned between 18 and 26 days of age. No difference was found between treatments for sow WW, BCS, IS, average daily feed intake, weaning litter wt, day 7 wt/d of age or piglet survivability. Exercise sows were leaner, sounder, and had more lesions at weaning than control sows (P<0.05). Exercise sows also had higher levels of salivary cortisol on average than control sows (P<0.05). These results indicate that increased movement of sows during lactation led to a decrease in back fat and an increase in soundness, with no affect on piglets.
The effects of furosemide on equine skeletal muscle satellite cell myogenesis and metabolism in vitro
Helsel, Patricia J. (Virginia Tech, 2020-01-29)
Thoroughbred racehorses undergo strenuous exercise which often leads to the occurrence of exercise-induced pulmonary hemorrhage (EIPH), in which capillaries rupture within the alveoli in the lungs causing bleeding. Severe cases of EIPH lead to epistaxis and may result in fatality. Presently, the loop diuretic furosemide is the only medication approved to mitigate the effects of EIPH. Often regarded in the racing industry as "performance enhancing" due to 4% weight loss ensued by its diuretic effect, it is unknown what effects furosemide may have on muscle recovery. Therefore, the objective of this study was to determine the effects various doses of furosemide may have on equine satellite cell (eqSC) myogenesis and metabolism. Mitotic index was increased (P<0.05) as a result of treatment with 100 µg/mL furosemide, a 10-fold pharmacological dose, in comparison to vehicle, but was not different (P>0.05) compared to the physiological dose of 10 µg/mL furosemide. Average cell number decreased (P<0.05) in the excess furosemide group compared to all other groups. Pax7 expression did not differ (P>0.05) between groups. Expression of the differentiation transcription factor myogenin, and embryonic sarcomeric myosin heavy chain decreased (P<0.05) when cells were treated with 100 µg/mL furosemide. Fusion index and myotube area decreased (P<0.05) as a result of treatment with excess furosemide. Glycogen concentration in myotubes was lower (P<0.05) following treatment with 100 µg/mL furosemide, while IGF-1 was unsuccessful in rescuing the effects of furosemide. Excess furosemide decreased expression of muscle creatine kinase while increasing expression of phosphoglucomutase 1, glycogen synthase 1, and glycogen branching enzyme 1 (P<0.05). Excess furosemide decreased basal oxygen consumption rate (OCR) and increased OCR after addition of oligomycin (P<0.05). Excess furosemide did not affect myotube glycolysis rates in vitro. In conclusion, furosemide inhibits muscle differentiation and oxidative metabolism in eqSCs.
The effects of hyaluronic acid and exercise on equine skeletal muscle
Gregg, Savannah Renee (Virginia Tech, 2023-08-18)
Unaccustomed, strenuous exercise can cause skeletal muscle damage that subsequently induces an acute inflammatory response in the tissue which is marked by an infiltration of leukocytes into the damaged muscle. To try and suppress the initial pro-inflammatory response in skeletal muscle of horses performing a single exercise stress test, a commercial sodium hyaluronate (HA) treatment was administered and tested for anti-inflammatory properties. Unfit, adult Thoroughbreds were intravenously injected three times with HA or received no injection at all (CON) over a 3-week period before performing a single submaximal exercise test. Gluteal muscle biopsies were collected before and 1 h after the completion of exercise for RNA-Seq and staining. The results indicated that HA treatment in horses down regulated genes associated with lymphocyte activation and cytokine production (Il17RA, OSCAR, LYL1, TLR1, TLR2, TLR8, TLR10) but did not irreversibly down regulate these genes with the addition of exercise. Exercise as a stressor did cause an acute inflammatory response in muscle which was seen through global expression of macrophage and neutrophil surface markers (NCF2, ELANE, CD168I). These results determine that HA treatment does act as an anti-inflammatory in equine skeletal muscle but does not possess prolonged effects with the initiation of inflammation.
The Effects of Resistance Wheel Running on Skeletal Muscle Function and Adaptation in C57BL/10SnJ Mice
Rodden, Gregory Robert (Virginia Tech, 2015-07-21)
Background: Resistance wheel running (RWR) can promote resistance-like training adaptations in mouse skeletal muscle (SkM), but its endurance-training effects are lesser known. Methods: Voluntary RWR was modulated as an exercise model to increase mouse hind-limb plantar-flexor torque and to promote endurance-training adaptations. Thirty male mice (cohort 1, n= 16; cohort 2, n= 14), were trained on a prototype RWR system that applied resistance relative to body mass (BM). Mice were sequentially, (1) screened for running ability (screening; 3-days); (2) trained with incremental adjustments to wheel loads (pre-training; 8-weeks); (3) grouped into cage-activity only (CA), and constant Low-0%, Med-15%, or High-25% BM resistance conditions (static training; 5-weeks); (4) trained with resistance adjusted in real-time (dynamic training; cohort 1, 7-weeks; cohort 2, 10-weeks); and (5) sacrificed for various assays. Plantar-flexor torque was determined during each training phase. After dynamic training, resistance runners in each cohort were sub-grouped post-hoc by work tertiles. Results: Wheel running distance varied between cohorts (cohort 2 > 1). During dynamic training, wheel running (±added-resistance) improved plantar flexor torque normalized to BM by 19% only in cohort 2 (p= 0.007). Muscle mass and cross-sectional area were unchanged. Runners in both cohorts (±added-resistance) improved maximal running capacity vs. CA-controls (+69% and +115%; both p < 0.05), but metabolic training adaptations were less evident. Conclusions: Wheel running promoted SkM strength and endurance, but there was a greater increase in endurance capacity than strength. This outcome may be due to adaptive signaling interference.
Energy Dense, Protein Restricted Diet Increases Adiposity and Perturbs Metabolism in Young, Genetically Lean Pigs
Fisher, Kimberly D.; Scheffler, Tracy L.; Kasten, Steven C.; Reinholt, Brad M.; van Eyk, Gregory R.; Escobar, Jeffery; Scheffler, Jason M.; Gerrard, David E. (PLOS, 2013-08-26)
Animal models of obesity and metabolic dysregulation during growth (or childhood) are lacking. Our objective was to increase adiposity and induce metabolic syndrome in young, genetically lean pigs. Pre-pubertal female pigs, age 35 d, were fed a high-energy diet (HED; n = 12), containing 15% tallow, 35% refined sugars and 9.1–12.9% crude protein, or a control corn-based diet (n = 11) with 12.2–19.2% crude protein for 16 wk. Initially, HED pigs self-regulated energy intake similar to controls, but by wk 5, consumed more (P<0.001) energy per kg body weight. At wk 15, pigs were subjected to an oral glucose tolerance test (OGTT); blood glucose increased (P<0.05) in control pigs and returned to baseline levels within 60 min. HED pigs were hyperglycemic at time 0, and blood glucose did not return to baseline (P = 0.01), even 4 h post-challenge. During OGTT, glucose area under the curve (AUC) was higher and insulin AUC was lower in HED pigs compared to controls (P = 0.001). Chronic HED intake increased (P<0.05) subcutaneous, intramuscular, and perirenal fat deposition, and induced hyperglycemia, hypoinsulinemia, and low-density lipoprotein hypercholesterolemia. A subset of HED pigs (n = 7) was transitioned back to a control diet for an additional six weeks. These pigs were subjected to an additional OGTT at 22 wk. Glucose AUC and insulin AUC did not improve, supporting that dietary intervention was not sufficient to recover glucose tolerance or insulin production. These data suggest a HED may be used to increase adiposity and disrupt glucose homeostasis in young, growing pigs.
Examining the Influence of Muscle Fiber Type on Protein Turnover Signaling in Growing Pigs
Seymour, Kacie Tinnesz (Virginia Tech, 2020-05-28)
Postnatal skeletal muscle growth occurs through myonuclear accretion and high protein turnover rate. While fiber type composition of the muscle could affect protein turnover rate, less is known about how fiber type influences the regulation of protein synthesis and degradation signaling pathways. Thus, the hypothesis of this work was that variation in fiber type composition will differentially affect the regulation of signaling pathways related to protein turnover in skeletal muscle hypertrophy in growing pigs. Downregulated protein synthesis signaling and reduced expression of type II MyHC isoforms have been reported in skeletal muscles of low birth weight (LBWT) neonatal pigs. Therefore, we sought to determine whether these changes are sustained until weaning and would explain the reduction in LBWT pig growth compared to their normal birth weight (NBWT) sibling at weaning. Another objective was to determine whether the regulation of protein turnover signaling pathways are correlated to fiber type differences in skeletal muscles. Our data suggest that the longissimus dorsi (LD, glycolytic) muscle of LBWT pigs experienced compensatory growth while the soleus (oxidative) remained proportionally smaller. Growth of the LD was accompanied by upregulation of translation initiation. Additionally, there was no difference in expression of MyHC isoforms between NBWT and LBWT pigs. These data suggest the rapid growth of the LD of LBWT pigs may be attributed to an upregulation of protein synthesis signaling and occurred only in glycolytic muscles. A caveat in LBWT pig model is that the reduction in type II MyHC at birth is not the only factor that could influence muscle growth, and that other factors may have confounded our results. This is why we aimed to use β-adrenergic agonist as a means to induce a shift fiber type in muscles to a more glycolytic phenotype. Our objective was to determine the influence of the β-adrenergic agonist Ractopamine (RAC) induced slow-to-fast fiber type transformation on the regulation of protein synthesis and degradation pathways. Although supplementation improved translational capacity, enhanced S6K1 phosphorylation, and reduced the abundance of calcium-dependent proteases, RAC feeding had no effect on body or muscle weights. These results suggest that a fiber type transformation without other physiological influences does not alter protein turnover signaling in favor of hypertrophy in growing pigs.
Exploring the Factors Contributing to the High Ultimate pH of Broiler Pectoralis Major Muscles Affected by Wooden Breast Condition
Baldi, Giulia; Yen, Con-Ning; Daughtry, Morgan R.; Bodmer, Jocelyn; Bowker, Brian C.; Zhuang, Hong; Petracci, Massimiliano; Gerrard, David E. (2020-05-08)
The elevated ultimate pH (pH(u)) found in wooden breast (WB) meat suggests an altered muscular energetic status in WB but also could be related to a prematurely terminated post-mortem pH decline. The aims of this study were to explore the factors contributing to the elevated pH(u) and establish whether the occurrence of WB defect alters muscle post-mortem carbohydrate metabolism and determine if the contractile apparatus reflects such changes. A total of 24 carcasses from Ross 308 male chickens were obtained from a commercial producer and harvested using commercial processing procedures. Carcasses were categorized into unaffected (NORM) and WB groups (n = 12 each), and samples were collected from cranial bone-in pectoralis major (PM) muscles at 15 min and 24 h post-mortem for the determination of pH, glycolytic metabolites, adenonucleotides, buffering capacity, phosphofructokinase (PFK) activity, and in vitro pH decline. Twenty-four additional deboned PM samples (12 NORM and 12 WB) were collected from the same processing plant to assess muscle histology and sarcomere length at four different locations throughout the PM muscle. Data show that the reduced glycolytic potential of WB muscles only partially explains the higher (P < 0.001) pH(u) of WB meat, as residual glycogen along with unaltered PFK activity suggests that neither glycogen nor a deficiency of PFK is responsible for arresting glycolysis prematurely. The dramatic reduction in ATP concentrations in the early post-mortem period suggests a defective ATP-generating pathway that might be responsible for the reduced pH decline in WB samples. Further, the addition of excess of ATPase extended post-mortem glycolysis of WB meat in an in vitro glycolytic system. WB-affected samples have longer (P < 0.001) sarcomeres compared to NORM, indicating the existence of compromised energy-generating pathways in myopathic muscles that may have had consequences on the muscle contraction and tension development, as in vivo, also during the post-mortem period. Considering the overall reduced glycolytic potential and the myodegenerative processes associated with WB condition, we speculate that the higher pH(u) of WB meat might be the outcome of a drastically impaired energy-generating pathway combined with a deficiency and/or a dysfunction of muscle ATPases, having consequences also on muscle fiber contraction degree.
Food Safe Alternatives to Methyl Bromide in Country Ham Production
Preisser, Richard Herman III (Virginia Tech, 2016-12-09)
Dry cured meat production is a costly and long term investment for producers. Ham mites (Tyrophagus putrescentiae) are a common pest of dry cured products and cause devastating effects, potentially nullifying producers' investments due to loss of salable product, as well as regulatory concerns. Methyl bromide, a chemical fumigant used to control mite populations, is damaging to stratospheric ozone and will no longer be available. Presently, no alternative control measure has been approved to combat the ham mite; therefore, it is essential to identify potential alternatives. Interest in safe alternatives to control arthropod pest populations is gaining momentum, and garlic (Allium sativum) has been used to control other arthropod species including the northern fowl mite, mosquitos, and aphids. We chose to explore the efficacy of garlic juice in controlling T. putrescentiae. Using a choice test design, approximately 65% of the inoculated mites colonized on the control ham cubes, while no mites remained on garlic juice-dipped cubes. Garlic was ineffective when examined for volatile efficacy, but was effective in direct contact assays. However, as garlic juice was aged and diluted, efficacy was reduced even after treatments with antioxidants, metal chelators, and pH neutralization. In total, garlic juice acted as a short term repellent and showed efficacy in contact models, but application is time sensitive due to variable enzymatic degradation.

Browsing by Author "Gerrard, David E."

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