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The objective of the study was to evaluate the effects of chromium (Cr) and methionine on myogenic gene expression, GLUT4 and insulin receptor (IR) synthesis, and amino acid uptake in differentiated bovine satellite cells. Cells were treated with 0, 1, or 10 μM of chromium acetate (CrAc) and 0, 1, or 10 mg/mL of methionine, with cells utilized for the amino acid assay receiving 0.1 μM instead of 1 μM of CrAc. The addition of 10 μM of Cr tended to downregulate AMPKα mRNA gene expression (P < 0.1). Myogenin was impacted by methionine and CrAc with high doses and low doses upregulating expression (P < 0.01). The ratio and protein levels of AMPKα to pAMPKα, GLUT4, and IR abundance were not affected (P > 0.1). Increase in time decreased concentrations of leucine, isoleucine, threonine, methionine, phenylalanine, glutamine, ornithine, lysine, and cysteine (P < 0.01) in conditioned media. Over time, alanine increased (P < 0.01). Methionine inclusion increased alanine, proline, glutamic acid, ornithine, and tryptophan concentrations, as well as decreased leucine, isoleucine, and cysteine (P < 0.01). CrAc only affected glutamine and tryptophan, which both increased with CrAc dose, whereas alanine decreased (P < 0.01). Methionine decreased over time within the 10 mg/mL group (P < 0.01). Tryptophan was generally unaffected but decreased in the 0 mg/mL group at 48 h. Cysteine decreased with a decreased dosage of CrAc at 24 h (P < 0.01). Lysine was generally unaffected by this interaction (P > 0.1), with the exception of the 0.1 μM treatment group at 24 h being higher (P < 0.01). CrAc affected the uptake of alanine, glutamine, and tryptophan (P < 0.01). Methionine inclusion increased alanine, proline, glutamic acid, ornithine, and tryptophan, as well as decreased leucine, isoleucine, and cystine (P < 0.01). Increased time saw a significant decrease in leucine, isoleucine, threonine, methionine, phenylalanine, glutamine, ornithine, lysine, and cystine (P < 0.01) and an increase in alanine (P < 0.01).

The objective of this study was to assess the effects of additional arginine (ARG) and lysine (LYS) on the regulatory factors associated with myogenic differentiation of bovine satellite cells and hypertrophy of myotubes. Bovine satellite cells were isolated from 3-mo-old Holstein bull calves (n=3) and subjected to a process of myogenic differentiation while exposed to varying doses of ARG or LYS. The experimental groups were as follows: (1) ARG dose-dependent (ARG: 0 [control], 60, and 120μM) with the presence of basal LYS (800μM) and (2) LYS dose-dependent (LYS: 0 [control], 50, and 100μM) with basal ARG (400μM) for the duration of 48 or 96 h. As a result of their alteration of myogenic regulatory factors (MRF), ARG and LYS might promote myogenic differentiation. Myoblast determination protein 1 (MyoD) and myogenin (MyoG) gene expression and protein abundance levels were elevated (P

Objective Our study aimed to investigate the effects of a 2% increase in dietary total digestible nutrients (TDN) value during the growing (7 to 12 mo of age) and fattening (13 to 30 mo of age) period of Hanwoo steers. Methods Two hundred and twenty Hanwoo steers were assigned to one of two treatments: i) a control group (basal TDN, BTDN, n = 111 steers, growing = 70.5%, early fattening = 71.0%, late fattening = 74.0%) or high TDN (HTDN, n = 109 steers, growing = 72.6%, early = 73.1%, late = 76.2%). Growth performance, carcass traits, blood parameters, and gene expression of longissimus dorsi (LD) (7, 18, and 30 mo) were quantified. Results Steers on the BTDN diets had increased (p≤0.02) DMI throughout the feeding trial compared to HTDN, but gain did not differ appreciably. A greater proportion of cattle in HTDN received Korean quality grade 1 (82%) or greater compared to BTDN (77%), while HTDN had a greater yield grade (29%) than BTDN (20%). Redness (a*) of LD muscle was improved (p = 0.021) in steers fed HTDN. Feeding the HTDN diet did not alter blood parameters. Steers fed HTDN diet increased (p = 0.015) the proportion of stearic acid and tended to alter linoleic acid. Overall, saturated, unsaturated, monounsaturated, and polyunsaturated fatty acids of LD muscle were not impacted by the HTDN treatment. A treatment by age interaction was noted for mRNA expression of myosin heavy chain (MHC) IIA, IIX, and stearoyl CoA desaturase (SCD) (p≤0.026). No treatment effect was detected on gene expression from LD muscle biopsies at 7, 18, and 30 mo of age; however, an age effect was detected for all variables measured (p≤0.001). Conclusion Our results indicated that feeding HTDN diet could improve overall quality grade while minimum effects were noted in gene expression, blood parameters, and growing performance. Cattle performance prediction in the feedlot is a critical decision-making tool for optimal planning of cattle fattening and these data provide both benchmark physiological parameters and growth performance measures for Hanwoo cattle feeding enterprises.

Abstract This study investigated the effects of dietary protein levels under various heat stress (HS) conditions on the growth performance and stress parameters in Korean native beef calves. Male calves (n = 40; initial BW = 202.2 ± 3.31 kg) were randomly assigned to climatic-controlled chambers with 3 × 3 factorial arrangements. Calves were assigned into three dietary protein levels (low protein; LP = 12.5%, medium protein; MP = 15%, and high protein; HP = 17.5%) and three HS levels [mild: temperature-humidity index (THI) = 74 to 76, moderate: THI = 81 to 83, and severe: THI = 89 to 91] with control (threshold: THI = 70 to 73 and dietary protein level 12.5%). The calves were subjected to ambient temperature (22 °C) for 7 days and subsequently to the temperature and humidity corresponding to the target THI level for 21 days. The data were analyzed using the repeated-measures analysis by the GLM procedure of SAS. As a result, average daily gain (ADG) was decreased (P

The present study was designed to determine the influence of all-trans retinoic acid (ATRA) on adipogenesis-related gene regulation in bovine intramuscular (IM) and subcutaneous (SC) adipose cells during differentiation. Bovine IM and SC adipocytes were isolated from three 19-mo-old, crossbred steers. Adipogenic differentiation was induced upon cultured IM and SC preadipocytes with various doses (0, 0.001, 0.01, 0.1, 1 µM) of ATRA. After 96 h of incubation, cells were harvested and used to measure the gene expression of CCAAT/Enhancer binding protein β (C/EBPβ), peroxisome proliferator-activated receptor (PPAR) γ, glucose transporter 4 (GLUT4), stearoyl CoA desaturase (SCD), and Smad transcription factor 3 (Smad3) relative to the quantity of ribosomal protein subunit 9 (RPS 9). Retinoic acid receptor (RAR) antagonist also tested to identify the effect of ATRA on PPARγ -RAR related gene expression in IM cells. The addition of ATRA to bovine IM decreased (p < 0.05) expression of PPARγ. The expression of PPARγ was also tended to be downregulated (p < 0.1) in high levels (10 μM) of ATRA treatment in SC cells. The treatment of RAR antagonist increased the expression of PPARγ in IM cells. Expression of C/EBPβ decreased (p < 0.05) in SC, but no change was observed in IM (p > 0.05). Increasing levels of ATRA may block adipogenic differentiation via transcriptional regulation of PPARγ. The efficacy of ATRA treatment in adipose cells may vary depending on the location.

Objective We hypothesized that Cr source can alter adipogenic-related transcriptional regulations and cell signaling. Therefore, the objective of the study was to evaluate the biological effects of chromium acetate (CrAc) on bovine intramuscular (IM) and subcutaneous (SC) adipose cells. Methods Bovine preadipocytes isolated from two different adipose tissue depots; IM and SC were used to evaluate the effect of CrAc treatment during differentiation on adipogenic gene expression. Adipocytes were incubated with various doses of CrAc: 0 (differentiation media only, control), 0.1, 1, and 10 μM. Cells were harvested and then analyzed by real-time quantitative polymerase chain reaction in order to measure the quantity of adenosine monophosphate-activated protein kinase-α (AMPK-α), CCAAT enhancer binding protein-β (C/EBPβ), G protein-coupled receptor 41 (GPR41), GPR43, peroxisome proliferator-activated receptor-γ (PPARγ), and stearoyl CoA desaturase (SCD) mRNA relative to ribosomal protein subunit 9 (RPS9). The ratio of phosphorylated-AMPK (pAMPK) to AMPK was determined using a western blot technique in order to determine changing concentration. Results The high dose (10 μM) of CrAc increased C/EBPβ, in both IM (p = 0.02) and SC (p = 0.02). Expression of PPARγ was upregulated by 10 μM of CrAc in IM but not in SC. Expression of SCD was also increased in both IM and SC with 10 μM of CrAc treatment. Addition of CrAc did not alter gene expression of glucose transporter 4, GPR41, or GPR43 in both IM and SC adipocytes. Addition of CrAc, resulted in a decreased pAMPKα to AMPKα ration (p

The objectives of this study were to determine the influence of package and muscle type on postmortem proteolysis and subsequent release of flavor-contributing free amino acids during storage. Beef strip loins and top sirloin butts (n = 20/subprimal) from USDA Low Choice carcasses were fabricated into 2.54-cm steaks (M. longissimus lumborum and M. gluteus medius) at 7 d postmortem. Steaks were randomly assigned to packaging treatments (carbon monoxide mother-bag [CO], high-oxygen modified atmosphere packaging [HIOX], polyvinyl overwrap [OW], or rollstock [ROLL]) and aged for an additional 14 d in dark storage. Steaks intended for OW were initially vacuum packaged during dark storage,then overwrapped just prior to display. Steaks were placed in coffin-style retail cases for 48 h under fluorescent lighting to simulate retail display. HIOX steaks exhibited the highest Warner-Bratzler shear force values (P < 0.05); the lowest desmin degradation rate (P < 0.05); the highest ratings for fishy, bitter, sour, and oxidized flavors; and the lowest overall tenderness scores (P < 0.05) and, in general, produced the lowest amount of free amino acids (P < 0.05) compared with all other treatments. Contrastingly, ROLL packaging produced the highest ratings for beef flavor identity, brown/roasted, bloody/serumy, and umami flavors (P < 0.05). Additionally, ROLL packaging exhibited (P < 0.05) greater desmin degradation in comparison with HIOX steaks. These data indicate that the optimum package for storage and aging is an anaerobic environment to maintain optimum flavor, tenderness, and postmortem proteolysis.

While satellite cells play a key role in the hypertrophy, repair, and regeneration of skeletal muscles, their response to heat exposure remains poorly understood, particularly in beef cattle. This study aimed to investigate the changes in the transcriptome, proteome, and proliferation capability of bovine satellite cells in response to different levels of heat stress (HS) and exposure times. Satellite cells were isolated from 3-mo-old Holstein bulls (body weight: 77.10 ± 2.02 kg) and subjected to incubation under various temperature conditions: 1) control (38 °C; CON), 2) moderate (39.5 °C; MHS), and extreme (41 °C; EHS) for different durations ranging from 0 to 48 h. Following 3 h of exposure to extreme heat (EHS), satellite cells exhibited significantly increased gene expression and protein abundance of heat shock proteins (HSPs; HSP70, HSP90, HSP20) and paired box gene 7 (Pax7; P < 0.05). HSP27 expression peaked at 3 h of EHS and remained elevated until 24 h of exposure (P < 0.05). In contrast, the expression of myogenic factor 5 (Myf5) and paired box gene 3 (Pax3) was decreased by EHS compared to the control at 3 h of exposure (P < 0.05). Notably, the introduction of HSP27 small interference RNA (siRNA) transfection restored Myf5 expression to control levels, suggesting an association between HSP27 and Myf5 in regulating the self-renewal properties of satellite cells upon heat exposure. Immunoprecipitation experiments further confirmed the direct binding of HSP27 to Myf5, supporting its role as a molecular chaperone for Myf5. Protein–protein docking algorithms predicted a high probability of HSP27–Myf5 interaction as well. These findings indicate that extreme heat exposure intrinsically promotes the accumulation of HSPs and modulates the early myogenic regulatory factors in satellite cells. Moreover, HSP27 acts as a molecular chaperone by binding to Myf5, thereby regulating the division or differentiation of satellite cells in response to HS. The results of this study provide a better understanding of muscle physiology in heat-stressed cells, while unraveling the intricate molecular mechanisms that underlie the HS response in satellite cells. [ABSTRACT FROM AUTHOR]

Our investigation elucidated the effects of severe temperature fluctuations on cellular and physiological responses in beef cattle. Eighteen Red Angus beef steers with an average body weight of 351 ± 24.5 kg were divided into three treatment groups: 1) Control (CON), exposed to a temperature-humidity index (THI) of 42 for 6 h without any temperature changes; 2) Transport (TP), subjected to a one-mile trailer trip with a THI of 42 for 6 h; and 3) Temperature swing (TS), exposed to a one-mile trailer trip with a THI shift from 42 to 72–75 for 3 h. Our findings indicate that TS can induce thermal stress in cattle, regardless of whether the overall temperature level is excessively high or not. Behavioral indications of extreme heat stress in the cattle were observed, including extended tongue protrusion, reduced appetite, excessive salivation, and increased respiratory rate. Furthermore, we observed a pronounced overexpression (P < 0.05) of heat shock proteins (HSPs) 20, 27, and 90 in response to the TS treatment in the longissimus muscle (LM). Alterations in signaling pathways associated with skeletal muscle growth were noted, including the upregulation (P < 0.01) of Pax7, Myf5, and myosin heavy chain (MHC) isoforms. In addition, an increase (P < 0.05) in transcription factors associated with adipogenesis was detected (P < 0.05), such as PPARγ, C/EBPα, FAS, and SCD in the TS group, suggesting the potential for adipose tissue accumulation due to temperature fluctuations. Our data illustrated the potential impacts of these temperature fluctuations on the growth of skeletal muscle and adipose tissue in beef cattle. [ABSTRACT FROM AUTHOR]

Our lack of understanding regarding how heat exposure affects major tissue growth and meat attributes impedes our ability to counteract more frequent climate extremes and promote profitability in the beef cattle industry. The objective of the study was to determine pathways that heat shock proteins (HSPs) regulate in beef cattle's skeletal muscle and adipose tissue growth and metabolism. Bovine satellite cells (BSCs) were isolated from the longissimus muscle of 3-month-old Holstein bulls (n = 5). Preadipose cells were isolated from the subcutaneous fat of 18-monthold Angus steers (n = 5) and induced adipogenic differentiation. Satellite, myofibers, and adipose cells were incubated at 38°C (control; CON), 39.5°C (moderate heat stress; MHS), and 41°C (extreme heat stress; EHS) and harvested for mRNA gene expressions, protein level, proteomics, immunostaining. Heat exposure cued bovine satellite cell proliferation and may increase the self-renewing satellite cell population. After 3 h of heat exposure, the mRNA gene expression and protein levels of Pax3 and Myf5 were downregulated, while HSPs 20, 27, 70, and 90 were upregulated. Small heat shock proteins, especially HSP27, appear to be essential in regulating satellite cell activity under heat stress. When HSP27 knock-down BSCs were exposed to EHS for 3 h, Myf5 gene expressions and protein levels returned to normal. This may indicate that HSP27 directly regulates Myf5 under heat stress and temporarily activates the self-renewal mechanism instead of committing myogenic differentiation. Results from proteomics showed that pathways related to oxidative phosphorylation, NADH dehydrogenase activity, and transmembrane transport were upregulated by EHS while MHS upregulated biosynthesis of amino acids, PI3K-Akt signaling pathway. Heat exposure during myogenic differentiation of satellite cells seemingly stimulates the commitment of myogenesis. Heat treatments increased mRNA gene expressions of IGF I, MHC I, MyoD, and myogenin and protein levels. Heat exposure also improved the muscle protein synthesis pathway by regulating the phosphorylation of mTOR, Akt, and P70S6. Heat stress triggered adipogenic differentiation and lipid storage, followed by increased expression of HSP. Extreme heat stress increased adipose cell growth by upregulating C/EBPα and PPARγ, key regulators of adipogenesis. Lipogenic genes FAS and SCD were also increased, accompanied by HSPs. Adipocytes exposed to EHS also increased intracellular lipid accumulation. Proteomic analysis revealed that carbon and pyruvate metabolism pathways were upregulated by MHS, whereas glycolysis/gluconeogenesis, protein processing in the endoplasmic reticulum, RNA transport, and biosynthesis of amino acids were upregulated by EHS. Cellular mechanisms related to skeletal muscle hypertrophy and adipose tissue growth are responsive in in-vitro settings; however, the results are controversial depending on cell type and animal species. Various factors such as metabolic, hormonal, and immunologic regulation need to be considered to accurately assess the effect of HS on the postnatal growth of major tissues at the animal level. [ABSTRACT FROM AUTHOR]

A randomized complete block design experiment with 30 yearling crossbred steers (initial average body weight [BW] = 297.6 ± 32.8 kg) fed a steam-flaked corn-based diet was used to evaluate finishing performance and carcass characteristics when provided with different concentrations of vitamin A (Rovimix A 1000; DSM Nutritional Products Ltd., Sisseln, Switzerland) subsequent to a depletion phase. Steers were blocked by BW (n = 5 blocks; 6 steers per block), assigned to pens (n = 2 steers per pen), and randomly assigned to one of the following dietary treatments: no added vitamin A (0IU; 0.0 IU/kg dry matter [DM] basis of additional vitamin A), vitamin A supplemented at the estimated National Academies of Sciences, Engineering, and Medicine (NASEM) requirement (2,200IU; 2,200 IU/kg of dietary DM of additional vitamin A), and vitamin A supplemented at 5× the estimated requirement (11,000IU; 11,000 IU/kg of dietary DM of additional vitamin A). The basal diet included minimal vitamin A activity (<200 IU of vitamin A activity/kg of dietary DM) via the provitamin A, beta-carotene. After all animals underwent a 91-d vitamin A depletion period, additional vitamin A was top-dressed at feeding via a ground corn carrier. Liver biopsy samples, BW, and blood were obtained on days −91, −35, 0, 28, 56, 84, and 112. Final BW was collected prior to shipping on day 112. Carcass data were collected by trained personnel upon harvest. Sera and liver samples were used to monitor circulating vitamin A and evaluate true vitamin A status of the cattle. Vitamin A status did not affect interim average daily gain or feed efficiency (G:F; P > 0.05). Throughout the duration of the study, dry matter intake for the 0IU cattle was depressed (P = 0.01). Differences were not observed across treatments for hot carcass weight, rib eye area, back fat thickness, kidney–pelvic–heart fat %, marbling score, or dressing percent (P ≥ 0.10). A treatment × day interaction occurred for both (P < 0.01) sera retinol and liver retinol during phase 2 of the trial. The treatments and sera retinol concentrations were incorporated into a repletion model, resulting in an estimation of liver retinol changes (P < 0.01; R2 = 0.682). However, models used to evaluate depleted animals were less effective. The current NASEM recommended that vitamin A requirement of 2,200 IU/kg is adequate for repletion of vitamin A status of feedlot steers. [ABSTRACT FROM AUTHOR]

A randomized complete block design experiment with 32 yearling crossbred steers (average body weight [BW] = 442 ± 17.0 kg) fed a steam-flaked corn-based diet was used to evaluate the effects of dietary Zn (KemTRACE Zn propionate 27; Kemin Industries, Inc., Des Moines, IA) supplementation on live growth performance, skeletal muscle fiber, and beta-adrenergic receptor (β-AR) characteristics during the finishing phase. Steers were blocked by BW (n = 4 blocks; 8 steers/block), assigned to pens (n = 4 steers/pen), and randomly assigned to the following treatments: control (CON; 0.0 g/[head (hd) · d] of additional Zn) or additional dietary Zn (ZnP; 1.0 g/[hd · d] additional Zn). The basal diet contained Zn (60 ppm dry matter basis) from ZnSO4; additional Zn was top-dressed at feeding. Ractopamine hydrochloride (RH; Optaflexx: Elanco Animal Health, Greenfield, IN) was included at 300 mg/(hd · d) for the final 28 d of the 111-d feeding period. Longissimus muscle biopsy samples, BW, and blood were obtained on days 0, 42, 79, and 107. Final BW was collected prior to shipping on day 111. Biopsy samples were used for immunohistochemical (IHC), mRNA, and protein analysis. Serum urea nitrogen (SUN) and nonesterified fatty acid (NEFA) concentrations were measured. Steers fed ZnP had a greater average daily gain (P = 0.02) and gain to feed ratio (G:F; P = 0.03) during the RH feeding period compared with CON. There were no differences (P > 0.05) in other growth performance variables, carcass traits, mRNA abundance, or relative protein concentration for fiber type and β-AR. Fiber types I and IIA had no differences in the cross-sectional area; however, the IIX area was greater for CON (P < 0.04) compared with ZnP and increased (P < 0.02) over time. There were no differences between treatments for the β1-AR density (P > 0.05) in skeletal muscle tissue throughout the study. A treatment × day interaction was observed in β2-AR density (P = 0.02) and β3-AR density (P = 0.02) during the RH feeding period, where the abundance of the receptors increased with ZnP but did not change in CON. Compared with CON, ZnP had greater (P < 0.01) mean NEFA concentrations. Mean SUN concentrations did increase by day (P < 0.01). Additional dietary Zn, supplied as Zn propionate, upregulates β2-AR and β3-AR and improves growth performance in feedlot steers during the RH feeding period, likely through a shift of resource utilization from lipogenesis to muscle maintenance and hypertrophy. [ABSTRACT FROM AUTHOR]

Guanidinoacetic acid (GAA) is an amino acid-like compound that acts as a precursor to creatine (CRE) when either made in the body or digested. Creatine is directly used by skeletal muscle tissue as an energy source with the potential to act as a growthpromoting agent. The study objectives were to evaluate the effects of various CRE concentrations on bovine satellite cells for the rate of proliferation and myogenic differentiation. Satellite cells (SC) were isolated from the Longissimus muscle of 3-month-old Holstein bulls (n = 5). Cells were seeded at a density of 1 × 104 cells/mL on 96-well plates and incubated with 0 (CON), 2.5, 5, 7.5, and 10 mM of CRE. The absorbance rate was measured at 0, 24, 48, 72, and 96 h of incubation. Cells for gene expression were plated on 6-well plates at a density of 1 × 105 in 10% FBS/DMEM. Following 24 h of adhesion, SC were incubated with 5 and 7.5mM CRE for 48 h. After which, cells were harvested after 48 h for Pax3, Pax7, and Myf5 mRNA gene expression analysis. To identify the effects of CRE during myogenic differentiation, SCs were induced myogenic differentiation. Upon reaching approximately 90% confluency, the growth medium was replaced by differentiation media (2% horse serum/DMEM) containing 0 (CON), 5, and 7.5 mM CRE. A two-way ANOVA and Tukey's HSD test were conducted regarding cell proliferation. A one-way ANOVA and Tukey's HSD test were performed for gene expression. Interaction of treatment against time was noted (P < 0.01) in Con, 2.5, 5, 7.5, and 10 mM CRE. Cell proliferation rate was influenced by CRE treatment (P < 0.01). At 72 h of incubation, all CRE treatments increased cell proliferation rate compared with Con (P < 0.05). At 96 h of incubation, cells treated with 2.5, 5, and 7.5 mM of CRE increased proliferation compared with Con (P < 0.05). At 96 h, CRE treatment 2.5, 5, and 7.5 mM increased proliferation rate compared with 10mM CRE treated cells (P < 0.05). No treatment effect was found in the mRNA gene expression of Pax7, Pax3, and Myf5 (P > 0.05). Cells incubated with CRE showed no change in mRNA gene expression of IGF-1 and Myogenin (P > 0.05), and a tendency was noted for S6KB1 increase expression under treatment (P = 0.0643). S6KB1 is a protein kinase that, through mTOR pathway expression, leads to an increase in cell growth, protein synthesis, and cell proliferation. Results suggest that the treatment of BSCs with CRE impacted proliferation, CRE at 5mM vs. 7.5 mM concentrations treatment of differentiated muscle cells led to a trend in altering S6KB1 gene expression. [ABSTRACT FROM AUTHOR]

Heat resistance depends on the breed of cattle and is important for genetic improvement under heat stress (HS). Study objectives were to investigate the heat resistance using peripheral blood mononuclear cells (PBMCs) and hair follicles in beef and dairy calves based on heat shock protein (HSP) 70 genetic polymorphisms. The hair follicles samples from sixty calves (6-monthold, 30 Hanwoo calves, and 30 Holstein calves) were collected for DNA extraction. The HSP70 genotype was analyzed based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) before the experiment. In study 1, PBMCs were isolated from 20 calves (10 Hanwoo calves; H-CC, H-C/-type, and 10 Holstein calves; D-CC, D-C/-type) and exposed to heat (37°C; Con and 42°C; HS) for 3 h. Cells were harvested and used for mRNA gene expression via RT-qPCR. Cell proliferation was measured using an ELISA kit. In study 2, hair follicles were collected from 20 calves (six times every 30 days; low-HS, medium-HS, and high-HS) and HSP70 gene expression was measured. Data were analyzed by two-way ANOVA and Tukey HSD test. Heat exposure decreased the cell proliferation rate (P < 0.05) in the D-CC and D-C/-groups compared with the H-C/C and H-C/- groups. The mRNA gene expression of HSP70 was greater (P < 0.05) in D-C/- group than in the H-CC and H-C/- groups after heat exposure. Gene expression of HSP70 of hair follicles was increased by high-HS level than those at the low-HS level. In addition, overexpression of HSP70 was noted (P < 0.05) in D-CC and D-C/- groups compared with the H-CC and H-C/- groups. Our results indicate that breeds and HSP70 genetic polymorphisms exhibit a distinctive pattern of immune cell proliferation and HSP70 profiles. The HSP70 gene expression in hair follicles can represent heat resistance in different breeds, and therefore, it can be used as a novel HS barometer. [ABSTRACT FROM AUTHOR]

Understanding the myogenic and self-renewal capability of satellite cells under heat stress (HS) is fundamental to coping with global warming in the beef cattle industry. Study objectives were to determine transcriptomic changes and proliferation capability of bovine satellite cells (BSCs) under moderate versus acute levels of HS and exposure times. Satellite cells were isolated from four three-month-old Holstein calves (semitendinosus) and cultured with 10% FBS/DMEM. Following 24h of attachment period, BSCs were incubated under the following temperature conditions 1) control (38°C; Con), 2) moderate (39.5°C; MHS) and extreme (41°C; EHS) and for various exposure times (0, 1, 3, 6, 12, 24, and 48 h). Cells were harvested and used for mRNA gene expression via RT-qPCR at each time point. Cell proliferation was measured using the ELISA kit. Data were analyzed by two-way ANOVA and Tukey HSD test. The expression of HSP70 was greatest (P < 0.05) in cells treated EHS at 1 and 3 h. Cells treated EHS overexpressed (P < 0.05) HSPB1 at 3, 6, 12, and 24 h. A similar pattern was observed (P < 0.05) for MyoD expression at 24 h after heat exposure. Contrarily, Myf5 and PAX3 were decreased (P < 0.05) by EHS compared to the Con at 3 h. Cell proliferation rate was enhanced (P < 0.01) in both MHS and EHS treated BSCs compared withthe Con at 48 h. Our results suggest that extreme heat exposure stimulates the HSPs (HSP70 and HSPB1) expression while modulating muscle regeneration by regulating myogenic regulatory factors (MyoD, Myf5) and PAX3. The transcriptional effect peaked after 3h of heat exposure, but the long-term (48h) exposure may activate the proliferation of BSCs. [ABSTRACT FROM AUTHOR]

Creatine (CRE) is an energy-storing molecule of skeletal muscle and is reported as potential growth promotants. With Guanidinoacetic acid (GAA) being a precursor to creatine, the potential to evaluate supplemental GAA's role in the body from a skeletal muscle focus is needed within the beef industry. Study objectives were to evaluate the effects of CRE and GAA on bovine satellite cells (BSCs) proliferation and myogenic potential. BSCs were obtained from three-month-old Holstein calves (n=3), harvested, and incubated with 10% FBS/DMEM. Following 24h of cell adhesion, BSCs were incubated with treatments: 1) Control, 2) 10mM GAA, and 3) 5mM CRE. Cell proliferation rate was measured at 0, 24, 48, 72, and 96h. In order to identify the effects of CRE and GAA during myogenic differentiation, satellite cells were incubated in a differentiation medium (2% horse serum/DMEM) containing 10mM GAA and 5mM CRE. After 48h, cells were harvested and used for mRNA gene expression (Myh7, MyoG, IGF-1, and S6KB1). One-way ANOVA and Tukey's HSD test were used for gene expression. Two-way ANOVA and Tukey's HSD test were conducted for cell proliferation assay. No interaction effect was noted (P > 0.05) between the effects of treatment against time in end output of cell proliferation. Cell proliferation rate was not altered (P > 0.05), with proliferation rate time measurement having a greater result of cell proliferation (P < 0.001). The expression of IGF-1 was overexpressed (P < 0.05) in GAA treated BSC during the myogenic differentiation. CRE increased (P < 0.01) MyoG expression. GAA and CRE did not alter Myh7 orS6KB1 mRNA gene expression. Results suggest that the treatment of BSCs with creatine or GAA may improve myogenic differentiation and promote skeletal muscle growth via IGF-1, respectively. [ABSTRACT FROM AUTHOR]