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The objective of this study was to create various pH/temp decline rates in hot-boned bull beef M. longissimus lumborum (LL) through a combination of electrical stimulation (ES) and pre-rigor holding temperature. The relationship between the pre-rigor interventions, the activities of µ-calpain and small heat shock proteins (sHSP), and the impacts on meat product quality were determined. Paired LL loins from 13 bulls were hot-boned within 40 min of slaughter, immediately ES and subjected to various holding temperatures (5, 15, 25, and 35°C) for 3 hr. The rate of muscle pH decline, sarcomere length, shear force, and proteolysis of muscle proteins were measured. ES-25°C had a longer sarcomere length compared to non-electrical stimulation samples. ES-25°C and ES-35°C samples had lower shear force values, higher µ-calpain activity and higher desmin, troponin-T, and sHSP degradation. The above findings suggest that pH/temp decline rates created in hot-boned muscle impacted muscle protein proteolysis by increasing the activity of proteases and degradation of sHSP.

Heat stress (HS) has depletory effects on intestinal morphology, induces metabolic changes, and disposes pigs to oxidative stress. Zinc has roles in gut health, nutrient and insulin mediated metabolism. To better understand the effects of cyclic heat and dietary Zn supplementation on gut integrity, carcass composition, and pork quality, commercial crossbred mixed-sex pigs (n = 400; initially 72.2 kg) were housed under either thermoneutral (TN; 18.9–16.7°C) or cycling HS conditions simulating chronic summer heat (30°C/26.7°C for 12h:12h on days 24–65) with acute heat periods of 32-33°C/29-30°C for 12h:12h on days 21–24, 42–45, and 63–65. Treatments were arranged in a 2×2×2 factorial with main effects of environment (HS vs. TN), added Zn level (50 vs. 130 mg/kg available Zn), and added Zn source (inorganic from ZnO vs. organic from Availa®Zn; Zinpro Corp, Eden Prairie, MN). Relative to TN, HS elevated (P < 0.050) body temperatures during the growing period. Heat stress was correlated with ileal villus height (r=-0.51, P = 0.015) and HSP-70 expression (r=0.46, P = 0.041). Growth was reduced such that carcasses from HS pigs were lighter (P = 0.011) and exhibited improved carcass quality with higher (P = 0.001) 24-hour loin pH, decreased (P = 0.034) drip loss, and greater (P < 0.050) subjective color and firmness scores compared to TN carcasses. Relative to TN, loin chops and sausage patties manufactured from the HS carcasses had similar oxidative stability (CIE L*a*b* color, 2-thiobarbituric acid reactive substances) throughout a 10-day simulated retail display. The HS induced fatty acid profile differences in the pork product but were not sufficient to shift IV (P > 0.10). Belly firmness and slice lean were also unaffected (P > 0.10) by HS. Zinc supplementation had minimal impact on the carcass quality characteristics studied. Further research is necessary to better understand the impact of HS duration, combination with additional stressors, and refine the ability to utilize thermal monitoring to manage negative impacts of HS.