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The roles of energy pathways in postmortem muscles are still debated. In this study, the contributions of different pathways to ATP production and pH variations were analyzed by using a kinetic model based on data from beef longissimus lumborum. Phosphocreatine represents over 92% of the initial ATP production but, after 24 h, glycolysis, phosphocreatine, myokinase reaction, and aerobic respiration contribute, respectively, 89.44%, 5.26%, 4.44%, and 0.86% of the cumulative amount of ATP produced. ATP hydrolysis and glycolysis result in 0.52 and 0.6 units of pH decline, respectively, at 24 h with ATP hydrolysis accounting for most of the early decline. Phosphocreatine, myokinase reaction, and aerobic respiration lead to, respectively, 0.08, 0.07, and 0.004 units of pH increase after 24 h though phosphocreatine is depleted within the first 30 min. Furthermore, electrical stimulation affects pH primarily through ATP hydrolysis and glycolysis. The initial muscle oxygen saturation level and phosphocreatine content affect pH but the influences are small.

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A kinetic model structure was developed to describe the major variations in energy metabolism and to gain further understanding of pH changes in postmortem muscle experimentally observed with an in vitro glycolytic system. Comparison with experiments showed that the model could describe the kinetics of major metabolites and pH under varied conditions. Optimized model parameters definitively and consistently showed the observed effects of mitochondria, indicating a desirable level of model complexity. Simulation and analysis of pH variations based on the model suggested that phosphofructokinase activity has the strongest impact on the rate and extent of postmortem pH decline. Postmortem pH is also influenced by rates of ATP hydrolysis and glycolysis, and to a much lesser extent, pH buffering capacity. Other reactions, including those mediated by creatine kinase, adenylate kinase, and AMP deaminase, have minimal effects on postmortem pH decline.

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Transportation of end-of-cycle hens (EOCH) may result in birds' experiencing metabolic stress, which changes muscle characteristics. This study evaluated the impacts of simulated transport on muscle characteristics of white-feathered EOCH (65-70 wk). The factorial arrangement included treatments of T/RH (-10°C uncontrolled RH [-10], 21°C with 30 [21/30] or 80% RH [21/80], 30°C with 30 [30/30] or 80% RH [30/80]), duration (4, 8, 12 h), and feather cover (105 well-feathered [WF], 105 poorly-feathered [PF]). A total of 210 hens/replicate/farm (farm=block; 3 total) were tested during the simulated transport. Crates (one/duration/replicate), divided in half for each feather cover (seven hens/side), were placed in a climate-controlled chamber. Prior to exposure, hens were fasted (6 h). BW was taken pre- and post-exposure, and the difference was calculated as live shrink. Post-exposure to the test conditions, birds were slaughtered and carcasses were analyzed for muscle characteristics. Data were analyzed as a randomized complete block design (farm of origin as block) with ANOVA (Proc Mixed, SAS 9.4; significance declared at P ≤ 0.05). Duration resulted in more weight loss for the birds (P < 0.01). Final pH measures (30 h post-mortem) were higher in hens exposed to -10 than 21/80, 30/30, and 30/80 and this difference was exacerbated with time (breast P < 0.01 and thigh P = 0.01). For muscle color, breast and thigh (both feather covers; P = 0.01) were darker in the -10 treatment while redness values were higher in EOCH exposed to this treatment (breast and thigh P < 0.01). Additionally, thigh muscle redness was higher in PF hens (P < 0.01). Thaw and cooking losses were impacted by T/RH and duration (thaw loss P = 0.03 and cook loss P = 0.04). Cook loss was also influenced by T/RH and feather cover with PF hen muscles losing less water during cooking in the -10 treatment (P = 0.01). Overall, the largest impact from transport was found in hens exposed for a longer duration to -10 antemortem compared to other treatments, demonstrating a significant impact on muscle characteristics from ante-mortem stress.

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A total of thirty pigs were experimentally slaughtered using gas (80% CO2 in air, 90 s; 30% CO2/70% N2O; 90 s) or electrical stunning (1.3 A, 10 s). Stunning may accelerate post-mortem muscle metabolism, due to psychological stress and/or muscle contractions. The specific effects of the stunning method were studied by limiting pre-stunning physical activity and stress: pigs were driven in a trolley from the rearing to the stunning site (6.5 m) and immediately slaughtered. Bleeding efficiency and carcass characteristics were similar and satisfactory for all stunning methods. Early post-mortem pH decline in the Longissimus lumborum was faster following gas compared to electrical stunning. The pH of other muscles was not influenced; color and drip loss showed minor effects. Hence, results are in contrast to current beliefs: compared to electrical stunning, following gas stunning, the stress and muscle contractions during the induction of unconsciousness have a slightly greater impact on Longissimus lumborum muscle metabolism; differences are minor and limited to certain muscles only.

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The objective of this study was to evaluate the effects of temperature (T)/relative humidity (RH) combinations and exposure duration (D) on the muscle tissue characteristics of layer pullets during simulated transport. While layer pullets are not processed for meat, muscle physiology can be used as an indicator to assess welfare. Pullets (n = 240) were randomly assigned to 1 of 5 T/RH combinations (-15°C uncontrolled RH [-15], 21°C 30%RH [21/30], 21°C 80%RH [21/80], 30°C 30%RH [30/30], and 30°C 80%RH [30/80]) and 2 D (4 or 8 h) in a 5 x 2 factorial arrangement (3 replications). Birds were weighed before exposure, crated (density 45.5 kg/m2) and exposed to the conditions above. After exposure, birds were weighed (live shrink calculated) and slaughtered using a small-scale facility. Postslaughter, carcasses were eviscerated, and an initial pH was obtained from the right breast and thigh. Final breast and thigh pH and color values (lightness [L∗], yellowness [b∗], and redness [a∗]) were obtained 30 h postslaughter. Left breast muscles were frozen and analyzed for thaw and cook loss 4 wk postslaughter. Data were analyzed as a randomized complete block design via ANOVA (Proc Mixed; SAS 9.4), with farm of origin as block. Differences were considered significant when P ≤ 0.05. Live shrink (kg) was higher for pullets exposed to 30/30 and 30/80 compared with those exposed to 21/80 (P = 0.04) and for pullets exposed for 8 h compared with 4 h (P < 0.01). Breast muscle thaw loss (%) was higher in pullets exposed for 4 h compared with 8 h (P = 0.01). Breast and thigh muscle a∗ were higher for pullets exposed to 30/30 compared with 21/30 (P = 0.02). Thigh muscle b∗ was lower for pullets exposed to -15 compared with 21/80 (P = 0.05). Breast b∗ was higher for pullets exposed for 8 h compared with 4 h (P = 0.04). The results from this study demonstrates that increasing exposure D had minor effects on pullet muscle characteristics. In addition, layer pullets coped well with thermal stressors associated with simulated transport.

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Identifying the molecular mechanisms of animal behaviour is an enduring goal for researchers. Gaining insight into these mechanisms enables us to gain a greater understanding of behaviour and their genetic control. In this paper, we perform Quantitative Trait Loci (QTL) mapping of tonic immobility behaviour in an advanced intercross line between wild and domestic chickens. Genes located within the QTL interval were further investigated using global expression QTL (eQTL) mapping from hypothalamus tissue, as well as causality analysis. This identified five candidate genes, with the genes PRDX4 and ACOT9 emerging as the best supported candidates. In addition, we also investigated the connection between tonic immobility, meat pH and struggling behaviour, as the two candidate genes PRDX4 and ACOT9 have previously been implicated in controlling muscle pH at slaughter. We did not find any phenotypic correlations between tonic immobility, struggling behaviour and muscle pH in a smaller additional cohort, despite these behaviours being repeatable within-test.

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PURPOSE: We evaluated muscle proton elimination following similar exercise in the same muscle group following two exercise modalities. METHODS: Seven rowers performed handgrip or rowing exercise for ~ 5 min. The intracellular response of the wrist flexor muscles was evaluated by 31P nuclear magnetic resonance spectroscopy, while arterial and venous forearm blood was collected. RESULTS: Rowing and handgrip reduced intracellular pH to 6.3 ± 0.2 and 6.5 ± 0.1, arterial pH to 7.09 ± 0.03 and 7.40 ± 0.03 and venous pH to 6.95 ± 0.06 and 7.20 ± 0.04 (P < 0.05), respectively. Arterial and venous lactate increased to 17.5 ± 1.6 and 20.0 ± 1.6 mM after rowing while only to 2.6 ± 0.8 and 6.8 ± 0.8 mM after handgrip exercise. Arterio-venous concentration difference of bicarbonate and phosphocreatine recovery kinetics (T50% rowing 1.5 ± 0.7 min; handgrip 1.4 ± 1.0 min) was similar following the two exercise modalities. Yet, intramuscular pH recovery in the forearm flexor muscles was 3.5-fold slower after rowing than after handgrip exercise (T50% rowing of 2 ± 0.1 vs. 7 ± 0.3 min for handgrip). CONCLUSION: Rowing delays intracellular-pH recovery compared with handgrip exercise most likely because rowing, as opposed to handgrip exercise, increases systemic lactate concentration. Thus the intra-to-extra-cellular lactate gradient is small after rowing. Since this lactate gradient is the main driving force for intracellular lactate removal in muscle and, since pHi normalization is closely related to intracellular lactate removal, rowing results in a slower pHi recovery compared to handgrip exercise.

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Purpose: To investigate the influence of ß-alanine (BA) supplementation on muscle carnosine content, muscle pH and the power-duration relationship (i.e., critical power and W'). Methods: In a double-blind, randomized, placebo-controlled study, 20 recreationally-active males (22 ± 3 y, V°O2peak 3.73 ± 0.44 L·min-1) ingested either BA (6.4 g/d for 28 d) or placebo (PL) (6.4 g/d) for 28 d. Subjects completed an incremental test and two 3-min all-out tests separated by 1-min on a cycle ergometer pre- and post-supplementation. Muscle pH was assessed using 31P-magnetic resonance spectroscopy (MRS) during incremental (INC KEE) and intermittent knee-extension exercise (INT KEE). Muscle carnosine content was determined using 1H-MRS. Results: There were no differences in the change in muscle carnosine content from pre- to post-intervention (PL: 1 ± 16% vs. BA: -4 ± 25%) or in muscle pH during INC KEE or INT KEE (P > 0.05) between PL and BA, but blood pH (PL: -0.06 ± 0.10 vs. BA: 0.09 ± 0.13) during the incremental test was elevated post-supplementation in the BA group only (P < 0.05). The changes from pre- to post-supplementation in critical power (PL: -8 ± 18 W vs. BA: -6 ± 17 W) and W' (PL: 1.8 ± 3.3 kJ vs. BA: 1.5 ± 1.7 kJ) were not different between groups. No relationships were detected between muscle carnosine content and indices of exercise performance. Conclusions: BA supplementation had no significant effect on muscle carnosine content and no influence on intramuscular pH during incremental or high-intensity intermittent knee-extension exercise. The small increase in blood pH following BA supplementation was not sufficient to significantly alter the power-duration relationship or exercise performance.

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A model based on enzyme kinetics was developed to predict differences in postmortem pH change in beef muscles as affected by cooling rate. For the calibration and validation of the model, pH and temperature measurements were conducted at different positions in M. biceps femoris following conventional carcass cooling or faster cooling of the muscle after hot boning. The glycogen conversion, and, hence, the pH fall, was observed to significantly vary with position and cooling regime but only during the initial hours of cooling. Comparison of the cooling regimes indicated that fast cooling following hot boning avoids heat shortening induced by the combined effect of high temperature and low pH.

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OBJECTIVE: An experiment was conducted to study the blood haematology, muscle pH, and serum cortisol changes in pigs with different levels of drip loss. METHODS: Two groups (low and high) of 20 animals were selected from 100 pigs based on drip loss. All [Duroc× (Large White×Landrace)] pigs were slaughtered according to standard slaughtering procedures. At exsanguinations, blood samples were taken for the haematological parameters and serum cortisol analysis. The muscle samples were taken from longissimus dorsi muscle to evaluate the muscle pH and drip loss. RESULTS: Haematological parameters of low drip loss group showed higher content of white blood cells and monocytes than high drip loss group (p<0.05). The low drip loss group had higher muscle pH at 45 min (p<0.05) and 24 h (p<0.001) post-mortem than the high drip loss group. However, there was no significant difference in serum cortisol levels (p>0.05). CONCLUSION: Drip loss is mainly affected by the muscle pH decline after slaughter and also might be affected by white blood cells and monocytes.

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This study investigates whether rectal temperature of pigs, prior to slaughter, can give an indication of the risk of developing pork with PSE characteristics. A total of 1203 pigs were examined, measuring the rectal temperature just before stunning, of which 794 rectal temperatures were measured immediately after stunning. pH30LT (M. Longissimus thoracis) and temperature of the ham (Temp30Ham) were collected from about 530 carcasses, 30 min after sticking. The results present a significant positive linear correlation between rectal temperature just before and after slaughter, and Temp30Ham. Moreover, pH30LT is negatively correlated with rectal temperature and Temp30Ham. Finally, a linear mixed model for pH30LT was established with the rectal temperature of the pigs just before stunning and the lairage time. This model defines that measuring rectal temperature of pigs just before slaughter allows discovery of pork with PSE traits, taking into account pre-slaughter conditions.

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Muscle glycogen concentration (MGC) and lactate (LA), activity of glycogen debranching enzyme (GDE), glycogen phosphorylase (GP) and adenosine monophosphate kinase (AMPK) were determined at 0.5h (T0) and 24h (T24) post-mortem in Longissimus dorsi samples from 38 steers that produced high pH (>5.9) and normal pH (<5.8) carcasses at 24h postmortem. MGC, LA and glycolytic potential were higher (P<0.05) in normal pH carcasses. GDE activity was similar (P>0.05) in both pH categories. GP activity increased between T0 and T24 only in normal pH carcasses. AMPK activity was four times higher in normal pH v/s high pH carcasses, without changing its activity over time. Results reinforce the idea that differences in postmortem glycogenolytic/glycolytic flow in L. dorsi of steers showing normal v/s high muscle pH at 24h, could be explained not only by the higher initial MGC in normal pH carcasses, but also by a high and sustained activity of AMPK and an increased GP activity at 24h postmortem.

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