S.M. Cruzen

Evidence of decreased muscle protein turnover in gilts selected for low residual feed intake

The objective of this study was to evaluate the contribution of muscle protein turnover (synthesis and degradation) to the biological basis for genetic differences in finisher pigs selected for residual feed intake (RFI). Residual feed intake is defined as the difference between expected feed intake (based on the achieved rate of BW gain and backfat depth of individual pigs) and the observed feed intake of the individual pig. We hypothesized that protein turnover would be reduced in pigs selected for low RFI. Twelve gilts from a line selected for 7 generations for low RFI and 12 from a contemporary line selected for 2 generations for high RFI were paired by age and BW and fed a standard corn-soybean diet for 6 wk. Pigs were euthanized, muscle and liver samples were collected, and insulin signaling, protein synthesis, and protein degradation proteins were analyzed for expression and activities. Muscle from low RFI pigs tended to have less μ- and m-calpain activities (P = 0.10 and 0.09, respectively) and had significantly greater calpastatin activity and a decreased μ-calpain:calpastatin activity ratio (P < 0.05). Muscle from low RFI pigs had less 20S proteasome activity compared with their high RFI counterparts (P < 0.05). No differences in insulin signaling intermediates and translation initiation signaling proteins [mammalian target of rapamycin (mTOR) pathway] were observed (P > 0.05). Postmortem proteolysis was determined in the LM from the eighth generation of the low RFI pigs versus their high RFI counterparts (n = 9 per line). Autolysis of μ-calpain was decreased in the low RFI pigs and less troponin-T degradation product was observed at 3 d postmortem (P < 0.05), indicating slowed postmortem proteolysis during aging in the low RFI pigs. These data provide significant evidence that less protein degradation occurs in pigs selected for reduced RFI, and this may account for a significant portion of the increased efficiency observed in these animals.

Proteomic changes to the sarcoplasmic fraction of predominantly red or white muscle following acute heat stress

UNLABELLED Acute heat stress negatively impacts both human health and livestock production. In order to characterize the skeletal muscle cellular response to acute heat stress, the muscle sarcoplasmic proteome was analyzed via 2-D DIGE. Pigs (n=8 per treatment) were exposed to one of the three treatments for 12 h: heat stress (HS; 37 °C), thermal neutral (TN; 21°C), or TN while pair-fed (PFTN; 21 °C, feed limited based on HS group consumption). After euthanasia, the semitendinosus muscle was excised, separated into predominately red (RST) and white (WST) fiber type portions, and sarcoplasmic proteins were extracted. Spots determined in 2D-DIGE to be different due to HS were identified using ESI-MS or LC-MS/MS. Several proteins involved in glycolysis, glycogenesis, and glycogenolysis were increased or modified, indicating enhanced glycolytic capacity in response to HS. In the WST, HS decreased abundance of tubulins and soluble actin and increased phosphorylated cofilin 2 abundance, indicating a loss of microtubule structure and a likely increase in stable actin microfilaments. HS increased manganese superoxide dismutase abundance, but decreased peroxiredoxin 2 abundance, indicating an antioxidant response to HS. The proteomic response to HS suggests marked cellular changes in carbohydrate metabolism, structure, and antioxidant machinery in skeletal muscle. SIGNIFICANCE This paper examines the proteome response of skeletal muscle to acute (short duration, high intensity) heat stress (HS). Defining changes in the sarcoplasm proteome increases our understanding of the mechanisms of how muscle responds to HS. Moreover, demonstration of a fiber type differential response to HS illustrates the dynamic nature of muscle. The experimental design of the experiment allows for the differentiation between the true effects of HS and HS-induced hypophagia. Data such as these will provide the foundation for developing future mitigating solutions and preventative therapies to reduce the detrimental effects of acute heat stress on muscle function and metabolism.

Carcass composition of market weight pigs subjected to heat stress in utero and during finishing.

Objectives were to investigate the effects of prolonged gestational and/or postnatal heat stress on performance and carcass composition of market weight pigs. Pregnant gilts were exposed to gestational heat stress (GHS, 28°C to 34°C, diurnal) or thermal neutral (18°C to 22°C, diurnal) conditions during the entire gestation or during the first or second half of gestation. At 14 wk of age (58 ± 5 kg), barrows were housed in heat stress (32°C, HS) or thermal neutral (21°C, TN) conditions. Feed intake and BW were recorded weekly, and body temperature parameters were monitored twice weekly until slaughter (109 ± 5 kg). Organs were removed and weighed, and loin eye area (LEA) and back fat thickness (BF) were measured after carcass chilling. Carcass sides were separated into lean, separable fat, bone, and skin components and were weighed. Moisture, lipid, and protein content were determined in the LM at the 10th rib. Data were analyzed using a split plot with random effect of dam nested within gestational treatment. Carcass measurements included HCW as a covariate to control for weight. Planned orthogonal contrast statements were used to evaluate the overall effect of GHS in the first half, second half, or any part of gestation. Gestational heat stress did not alter postnatal performance or most body temperature parameters (P > 0.10). However, ADFI in the finishing period was increased (P < 0.05) in response to GHS, particularly in pigs receiving GHS in the first half of gestation. Gestational heat stress during the first half of gestation decreased head weight as a percent of BW (P = 0.02), whereas GHS in the second half of gestation decreased bone weight as a percent of BW (P = 0.02). Heat stress reduced ADG, BW, and HCW (P < 0.0001). Lean tissue was increased in HS pigs on both a weight and percentage basis (P < 0.0001), but LEA was similar to TN carcasses (P = 0.38). Carcasses from HS barrows also had less carcass separable fat (P < 0.01) and tended to have less BF (P = 0.06) compared with those from TN barrows, even after controlling for HCW. However, percent intramuscular fat did not differ between treatments (P = 0.48). The LM from HS carcasses had a greater moisture to protein ratio (P = 0.04). HS barrows also had decreased heart (P < 0.001) and kidney (P < 0.0001) as a percent of BW compared with TN pigs. In summary, GHS may affect head and bone development, subsequently affecting carcass composition. Chronic HS during finishing results in longer times to reach market weight and a leaner carcass once market weight is achieved.

Postmortem proteolysis in three muscles from growing and mature beef cattle

The objective of this study was to determine calpain system activity and postmortem protein degradation in three muscles from growing (n=6, 7.3 ± 0.5 months) and mature (n=6, 106.7 ± 43.1 months) beef cattle. The ratio of μ-calpain:total calpastatin activity tended to be lower in mature animals (P=0.08), suggesting reduced potential for proteolysis. Additionally, muscles from the mature group had greater calpastatin activity compared to calves at 6 days postmortem and had less μ-calpain autolysis and troponin-T and titin degradation during the aging period (P<0.01). Between the longissimus, semimembranosus, and triceps brachii muscles, the triceps brachii had the least postmortem proteolysis, with greater calpastatin activity and less troponin-T and titin degradation compared to other muscles (P<0.01). These data suggest that calpastatin activity in muscle from older animals is more persistent postmortem. This difference may contribute to the decreased protein degradation and increased toughness of beef from mature cattle, even after aging.

Effect of low voltage electrical stimulation on protein and quality changes in bovine muscles during postmortem aging

This experiment was conducted to determine the influence of low voltage electrical stimulation (ES) on the tenderness development of beef round muscles. Eight steers were slaughtered, and ES applied to one side of each carcass within 90 min of exsanguination. Steaks from M. longissimus dorsi, semimembranosus, adductor, and gracilis were vacuum packaged and aged at 4 °C for 9 d. Star probe, sensory evaluation, Western blot assays of troponin-T and μ-calpain autolysis and 2D-DIGE were conducted. ES resulted in accelerated (P<0.05) pH decline of the longissimus in the first 24h postmortem. ES did not influence (P>0.05) proteolysis and tenderness, but did alter the predominance of metabolic proteins in the soluble fraction of muscle. Aging for 9 d improved tenderness (P<0.05). The data confirmed that low voltage ES at 90 min of exsanguination had no effect on proteolysis and tenderness development in the longissimus dorsi, semimembranosus, adductor or gracilis in beef.

Effect of early postmortem enhancement of calcium lactate/phosphate on quality attributes of beef round muscles under different packaging systems.

The objective was to determine the influence of calcium lactate/phosphate enhancement on quality of beef round cuts in high-oxygen modified atmosphere (HiOx-MAP; 80% O2/20% CO2). Mm. semimembranosus (SM), semitendinosus (ST), and adductor (AD) were divided and assigned to water-injected control (CON), 3mM phosphate (STP), or 200mM calcium lactate/3mM phosphate (CAL/STP) treatments at 24h postmortem. Steaks (n=10) were vacuum packaged (VAC) and stored for 9days, then displayed for 7days in VAC or HiOx-MAP. Lipid oxidation, pH, surface color, star probe, and sensory characteristics were evaluated. HiOx-MAP resulted in greater lipid oxidation, more discoloration, and decreased sensory quality of steaks (P<0.05) compared to VAC. However, CAL/STP enhancement significantly reduced lipid oxidation of all steaks, decreased ST and SM star probe values, and improved tenderness of HiOx-MAP packaged AD and SM (P<0.05). Results suggest that CAL/STP enhancement has beneficial effects on lipid stability and sensory attributes of beef round cuts under HiOx-MAP.