Glycogen depletion patterns in myofibres of cattle during stress

The impact of weather on the incidence of dark cutting in Australian feedlot cattle

This study conducted a retrospective analysis of historical Meat Standard Australia (MSA) carcass data in combination with Bureau of Meteorology (BOM) weather data, to evaluate the relationship between climatic conditions prior to feedlot departure on the incidence of dark cutting grain-fed beef. Data records for 2,795,754 carcasses from 17 commercial feedlots over a 6-year period were evaluated within this study. Carcasses were consigned to 16 abattoirs. Weather data from BOM were recorded at 30-min intervals and were obtained from weather stations with the closest proximity to each feedlot. These data were used to calculate the Temperature Humidity Index (THI). Climatic data were amalgamated into daily observations and a series of predictors including ambient temperature (T_A, °C), relative humidity (RH, %), wind speed (WS, m/s), rainfall (mm) and THI. In addition, lag interactions from 24 h out to 28 days prior to exiting the feedlot were generated. The incidence of dark cutting was determined as percentage per cohort with an ultimate pH > 5.7. Data were analysed using three models: model 1 included feedlot, abattoir, hormone growth promotant status and sex as fixed effects. Model 2 incorporated the fixed effects within model 1 and minimum, maximum and standard deviation (SD) of T_A and RH, daily range in T_A, average WS and rainfall as random effects. Model 3 incorporated minimum, maximum, range and SD of THI, average WS and rainfall as random effects in addition to the fixed effects of model 1. The incidence of dark cutting within feedlot had a 10.1% range in estimated means with the lowest incidence was observed at feedlot 17 (0%) and highest incidence at feedlot 10 (10.1%). The inclusion of the climatic variables in model 2 and model 3 accounted for an additional 0.1 to 0.2% of the incidence of dark cutting carcasses. Higher maximum T_A, RH and THI in the 3 to 28 days prior to consignment were all associated with an increased incidence of dark cutting (P < 0.05), but not in the 48 h preceding consignment (P > 0.05). Low minimum T_A and low THI were also associated with an increase the incidence of dark cutting across all lag periods (P < 0.05). Increased variation in THI and T_A in the 48 h prior to consignment increased dark cutting (P < 0.05) while increased standard deviation (SD) of temperature and THI range also increased dark cutting in the 14 and 28 day prior to feedlot exit (P < 0.05). Smaller minimum ranges in T_A in the 28 days prior to consignment also reduced dark cutting (P < 0.05). Climatic conditions accounted for a further 0.1 to 0.2% of the incidence of dark cutting, whereas animal management factors, feedlot and abattoir were able to account for 21% of dark cutting. These data suggest that climatic conditions appear to have an inherent role in the incidence of dark cutting, albeit a small impact. Regardless, understanding the influence of climatic conditions on dark cutting allows for the implementation of management strategies within the supply chain to further reduce the impact of climatic conditions on grain-fed cattle.

Are muscle fiber types different between normal and dark-cutting beef?

Muscle fiber (MF) characteristics of Longissimus thoracis (LT) muscles from heifer (n = 11) and steer (n = 12) carcasses graded Canada AA (AA, normal, n = 4/sex) or dark-cutting (Canada B4) were examined and related to beef quality. Atypical (AB4, pH < 5.9, n = 4/sex) and typical (TB4, pH > 5.9, n = 3 and 4 for heifers and steers, respectively) dark-cutting carcasses were represented. Muscle fiber type proportions did not differ between AA, AB4 and TB4 muscles, although type I and IIB muscle fiber diameters were greater in TB4 than in AA LT. That AB4 muscle fiber proportions were not different from AA and TB4 muscles suggests that the increased MF diameter of TB4 muscle was due to water retained by muscle proteins at high ultimate pH, as evidenced by decreased cooking loss. Dark-cutting was therefore unrelated to muscle fiber proportions, and increased Type I and IIB diameters in dark cutting LT were likely driven by elevated intramuscular ultimate pH.

Evaluation of skin-on goat meat processing on processing efficiency, carcass yield, meat quality, and sensory attributes

The objective of this study was to evaluate the properties of skin-on and skin-off goat processing and carcasses for processing efficiency, fabrication time, biochemical factors, and sensory attributes for stewed goat meat. Thirty-one goats were harvested in 2 separate experiments, either skin-on (n = 16) or off (n = 15). The carcasses were fabricated into four primals and each primal was cut into cubes. Processing efficiency, carcasses yield, collagen content, moisture, lipid, ultimate pH, and sensory attributes were measured, and multivariate regression analysis were conducted. The skin-on group had greater overall yield compared to the skin-off group (P < 0.01). Consumers rated goat shoulder meat with the highest overall liking compared to the other primals (P < 0.01), regardless of skin present (P > 0.10). Finally, lipid % was found to be the most essential palatability trait to American Asian consumers.

Quality of Death in Fighting Bulls during Bullfights: Neurobiology and Physiological Responses

During bullfights, bulls undergo physiometabolic responses such as glycolysis, anaerobic reactions, cellular oedema, splenic contraction, and hypovolemic shock. The objective of this review article is to present the current knowledge on the factors that cause stress in fighting bulls during bullfights, including their dying process, by discussing the neurobiology and their physiological responses. The literature shows that biochemical imbalances occur during bullfights, including hypercalcaemia, hypermagnesaemia, hyperphosphataemia, hyperlactataemia, and hyperglycaemia, associated with increased endogenous cortisol and catecholamine levels. Creatine kinase, citrate synthase, and lactate dehydrogenase levels also increase, coupled with decreases in pH, blood bicarbonate levels, excess base, partial oxygen pressure, and oxygen saturation. The intense exercise also causes a marked decrease of glycogen in type I and II muscle fibres that can produce myoglobinuria and muscular necrosis. Other observations suggest the presence of osteochondrosis. The existing information allows us to conclude that during bullfights, bulls face energy and metabolic demands due to the high intensity and duration of the exercise performed, together with muscular injuries, physiological changes, and high enzyme concentrations. In addition, the final stage of the bullfight causes a slow dying process for an animal that is sentient and conscious of its surroundings.

Cattle production practices and the incidence of dark cutting beef

The effects of cattle sex, production system, growth promotant use, slaughter season, carcass phenotype, and pre-slaughter cattle management on the incidence of beef carcasses grading Canada B4 (dark cutting) were investigated using two data sets (A, n = 2009, and B, n = 86,408) containing data from cattle that produced Canada Prime, AAA, AA, A, and B4 carcasses. The probability of producing a Canada B4 carcass was greater (P < .0001) for heifers than steers in both data sets, with the likelihood of dark cutting decreasing with increased carcass weight in heifers in data set B. The incidence of dark cutting was increased (P < .0001) in Winter-born calf-fed (WC) and Fall-born calf-fed (FC) heifers. Production system and phenotype appear to interact to influence the incidence of dark cutting.

Association of ultimate pH and stress-related blood variables in cattle

The objective of this study was to investigate the relationship between ultimate pH (pHu) and stress-related blood variables. Of 50 cattle in total, blood samples from 6 cattle which exhibited high (≥6.10) pHu (dark-cutting) were collected, along with the same number of low pHu and intermediate pHu cattle (5.40-5.80; 5.80-6.10, respectively) to determine the concentration of plasma cortisol, glucose, lactate, creatine kinase, lactate dehydrogenase, haptoglobin and serum amyloid A protein. Compared to cattle with low pHu, high pHu cattle showed higher plasma cortisol, glucose, lactate, creatine kinase and lactate dehydrogenase levels at exsanguination. But the concentration of haptoglobin and serum amyloid A protein showed no significant differences among three pH groups. These results imply that measuring plasma cortisol, glucose, lactate, creatine kinase, or lactate dehydrogenase levels at exsanguination may be useful to identify the dark-cutting beef condition.

Postmortem Aging of Beef with a Special Reference to the Dry Aging

Animal muscles are stored for specific period (aging) at refrigerated temperatures, during and after which the living muscles start to convert into meat and thus, attain certain superior properties in the final product. Proteolysis, lipolysis, and oxidation are the major biochemical processes involved during the postmortem aging of meat that affect the tenderness, juiciness, and flavor, as well as sometimes may introduce certain undesirable traits. This review analyzes the role of pre- and post-mortem factors that are important for aging and their effect on the chemical and physical changes in the “dry- and wet-aged meat.” Thus, if the meat processing manufacturers optimize the effects of aging for specific muscles, the palatability, color, and the shelf life of the aged meat products could be significantly enhanced.

Can potential for dark cutting be predicted by phenotype? Relationship between sex, carcass characteristics, and the incidence of dark cutting beef

Recent research indicated that reduced carcass muscling and weight are associated with beef dark cutting. Existing data from a single farm (44 heifers, 136 steers) from three normal beef quality grades (Canada AAA, AA, A) and the dark cutting grade (Canada B4) (n = 35, 106, 28, and 11, respectively) were used to identify relationships between sex, live animal, and carcass characteristics and the incidence of dark cutting. Categorical modelling showed a trend (P = 0.106) for heifer carcasses to have a greater probability [11.36 ± 4.78% standard error of the mean (SEM)] of dark cutting than carcasses from steers (4.4 ± 1.76% SEM). Mixed model analysis of variance indicated dark cutting heifers weighed less than cattle from normal grades at weaning (P = 0.0229) and slaughter (P = 0.0295). Logistic regression revealed that the probability of each carcass grade occurring was influenced by dry matter intake (DMI) (P = 0.0034), and the probability of dark cutting was lowest (P = 0.0286) in cattle with carcasses greater than 300 kg. Results suggested that cattle at risk of dark cutting may be identified by weight, average daily gain (ADG), and feed intake.

Induction of tissue- and stressor-specific kinomic responses in chickens exposed to hot and cold stresses

Defining cellular responses at the level of global cellular kinase (kinome) activity is a powerful approach to deciphering complex biology and identifying biomarkers. Here we report on the development of a chicken-specific peptide array and its application to characterizing kinome responses within the breast (pectoralis major) and thigh (iliotibialis) muscles of poultry subject to temperature stress to mimic conditions experienced by birds during commercial transport. Breast and thigh muscles exhibited unique kinome profiles, highlighting the distinct nature of these tissues. Against these distinct backgrounds, tissue- and temperature-specific kinome responses were observed. In breast, both cold and hot stresses activated calcium-dependent metabolic adaptations. Also within breast, but specific to cold stress, was the activation of ErbB signaling as well as dynamic patterns of phosphorylation of AMPK, a key regulatory enzyme of metabolism. In thigh, cold stress induced responses suggestive of the occurrence of tissue damage, including activation of innate immune signaling pathways and tissue repair pathways (TGF-β). In contrast, heat stress in thigh activated pathways associated with protein and fat metabolism through adipocytokine and mammalian target of rapamycin (mTOR) signaling. Defining the responses of these tissues to these stresses through conventional markers of pH, glycolytic potential, and meat quality offered a similar conclusion of the tissue- and stressor-specific responses, validating the kinome results. Collectively, the results of this study highlight the unique cellular responses of breast and thigh tissues to heat and cold stresses and may offer insight into the unique susceptibilities, as well as functional consequences, of these tissues to thermal stress.

Shotgun proteomics reveals physiological response to ocean acidification in Crassostrea gigas

BACKGROUND

Ocean acidification as a result of increased anthropogenic CO2 emissions is occurring in marine and estuarine environments worldwide. The coastal ocean experiences additional daily and seasonal fluctuations in pH that can be lower than projected end-of-century open ocean pH reductions. In order to assess the impact of ocean acidification on marine invertebrates, Pacific oysters (Crassostrea gigas) were exposed to one of four different p CO2 levels for four weeks: 400 μatm (pH 8.0), 800 μatm (pH 7.7), 1000 μatm (pH 7.6), or 2800 μatm (pH 7.3).

RESULTS

At the end of the four week exposure period, oysters in all four p CO2 environments deposited new shell, but growth rate was not different among the treatments. However, micromechanical properties of the new shell were compromised by elevated p CO2. Elevated p CO2 affected neither whole body fatty acid composition, nor glycogen content, nor mortality rate associated with acute heat shock. Shotgun proteomics revealed that several physiological pathways were significantly affected by ocean acidification, including antioxidant response, carbohydrate metabolism, and transcription and translation. Additionally, the proteomic response to a second stress differed with p CO2, with numerous processes significantly affected by mechanical stimulation at high versus low p CO2 (all proteomics data are available in the ProteomeXchange under the identifier PXD000835).

CONCLUSIONS

Oyster physiology is significantly altered by exposure to elevated p CO2, indicating changes in energy resource use. This is especially apparent in the assessment of the effects of p CO2 on the proteomic response to a second stress. The altered stress response illustrates that ocean acidification may impact how oysters respond to other changes in their environment. These data contribute to an integrative view of the effects of ocean acidification on oysters as well as physiological trade-offs during environmental stress.

Regulation of post-mortem glycolysis in ruminant muscle

As a tissue, muscle has the unique ability to switch its metabolic source of ATP, the energy currency underpinning muscle function. During oxygen debt, such as that occurring immediately following the death of animals, anaerobic metabolism is initiated in an attempt to restore homeostasis within the muscle. The cascade of biochemical events that are initiated is paramount in the context of meat quality. This review revisits this reasonably well-known subject but takes a new perspective by drawing on the understanding outside the traditional discipline of meat science. Our understanding of the intrinsic regulators of glycolytic flux has improved but knowledge gaps remain. Further efforts to understand how the glycolytic enzyme kinetics are influenced by both pre- and post-slaughter factors will be beneficial in the ongoing quest to maximise fresh meat quality.

Muscle glycogen depletion pattern in halothane-gene-free pigs at slaughter and its relation to meat quality

Muscle fibre type composition and glycogen depletion pattern at slaughter as related to meat quality, were studied in M. longissimus dorsi of halothane-gene-free Swedish Yorkshire pigs fed a high (n=19; 10 entire males and 9 gilts) or a low (n=18; 10 entire males and 8 gilts) protein diet. The muscle consisted of, on average, 8% type I, 9% type IIA and 83% type IIB fibres. Muscle fibre areas were significantly smaller in entire male pigs than in gilts irrespective of fibre type. There were no marked differences in muscle characteristics between pigs fed the low and high protein diets. Low glycogen concentrations were found in most type I and type IIA muscle fibres, while a greater variation in glycogen content was evident in type IIB fibres. The pigs were divided into two groups according to the proportion of glycogen depleted IIB fibres (more or less than 30% depleted IIB fibres). In the group where 30% or more of the type IIB fibres were glycogen depleted, a tendency toward DFD meat (dry, firm, dark) was seen, as the meat had higher ultimate pH (5·62 vs 5·52; p=0·02), lower drip loss (2·7% vs 4·4%; p=0·007) and lower reflectance value (darker meat; 16·5 vs 20·6 EEL units; p=0·0005), compared with the group with less than 30% depleted IIB fibres. No difference in total glycogen content was found between these two groups. This indicates that the distribution of glycogen in different fibre types seems to be of importance for the ultimate meat quality.

Broiler chicken thigh and breast muscle responses to cold stress during simulated transport before slaughter

The effect of acute cold exposure was assessed on broiler physiology, breast and thigh muscle metabolites, and meat quality. In total, 160 male birds at ages of 5 and 6 wk were exposed to temperatures of -9 to -15°C (cold stressed) and +20°C (control) in a simulated transport chamber for 3 h before slaughter followed by 0 or 2 h of lairage. Bird physiology parameters, including core body temperature, live shrink, blood glucose, and muscle temperature, were assessed. Core body temperature was monitored every minute using i-Button data loggers, and live shrink and blood glucose were assessed. Total glucose and lactate concentrations at 30 h postmortem, as well as ultimate pH (pH(u)), color, and water-holding attributes were evaluated on pectoralis major muscle of breast and iliotibialis muscle of thigh. Birds were grouped based on their microclimate temperature to control and cold-stressed groups (0 to -8, -8 to -11, and -11 to -14°C). Significant (P < 0.05) decreases in core body temperature and breast and thigh muscle temperatures were observed at simulated transport temperatures below 0°C. In addition, higher (P < 0.05) live shrink and lower blood glucose values were observed as a result of 3-h exposure to temperatures below 0°C, exacerbated as temperature decreased further below -8°C. Thigh muscle was almost depleted of glycogen reserve compared with a significant but small reduction in breast muscle glycogen when exposure temperature was below -8°C. Similarly, much greater effects were observed on thigh pH(u) and quality attributes compared with breast. In addition, 84% incidence of the dark, firm, dry quality defect was observed in thigh meat (pH(u) > 6.4, L* < 44) compared with 42% incidence of dark, firm, dry in breast meat (pH(u) > 6.1, L* < 46) when transportation temperature was below 0°C. Results of this study showed that thigh muscle was affected more severely than breast muscle by exposure to cold temperatures before slaughter.

Strategies to promote farm animal welfare in Latin America and their effects on carcass and meat quality traits

Several initiatives, including research and development, increasing stakeholders' awareness and application of legislation and recommendation, have been carried out in Latin America to promote animal welfare and meat quality. Most activities focused on the impact of pre-slaughter conditions (facilities, equipment and handling procedures) on animal welfare and meat quality. The results are encouraging; data from Brazil, Chile and Uruguay showed that the application of the improved pre-slaughter handling practices reduced aggressive handling and the incidence of bruised carcasses at slaughter in cattle and pigs. These outcomes stimulated some to apply animal welfare concepts in livestock handling within the meat production chain as shown by the increasing demand for personnel training on the best. To attend this demand is important to expand local studies on farm animal welfare and to set up (or maintain) an efficient system for knowledge transfer to all stakeholders in the Latin America meat production chains. However, it is clear that to promote the long-term progress in this field is important to deliver practical solutions, assuring that they match the technical and financial conditions of those who are the target of training programs.

Effects of muscle cortisol concentration on muscle fiber characteristics, pork quality, and sensory quality of cooked pork

The effect of muscle cortisol concentration on muscle fiber characteristics and technological and sensory quality of pork was investigated. With the exception of the percentage of type IIA fibers, muscle fiber characteristics were not associated to cortisol levels. However, muscle cortisol concentration was positively associated with muscle pH(24h) (r = 0.23, P<0.05) and negatively associated with drip loss (r = -0.49, P<0.001), lightness (r = -0.24, P<0.05), shear force (r = -0.25, P<0.05), and texture profile analysis-hardness (r = -0.35, P<0.01). Additionally, the water-holding capacity of meat samples was affected by cortisol levels, with lower cortisol concentrations associated with less tender samples. These results indicate that the concentration of cortisol in the muscle is related with meat quality as well as the sensory quality of cooked pork.

Preslaughter handling effects on pork quality and glycolytic potential in two muscles differing in fiber type composition

The objective of the present experiment was to investigate the effects of transportation, lairage, and preslaughter stressor treatment on glycolytic potential and pork quality of the glycolytic longissimus and the oxidative supraspinatus (SSP) or serratus ventralis (SV) muscles. In a 2 x 2 x 2 factorial design, 384 pigs were assigned randomly either to short (50 min) and smooth or long (3 h) and rough transport, long (3 h) or short (< 45 min) lairage, and minimal or high preslaughter stress. Muscle samples were taken from the LM at 135 min and from the SSP at 160 min postmortem for determination of the glycolytic potential and rate of glycolysis. At 23 h postmortem, pork quality was assessed in the LM and the SV. Effects of transport and lairage conditions were similar in both muscle types. Long transport increased (P < 0.01) the glycolytic potential and muscle lactate concentrations compared with short transport. Both long transportation and short lairage decreased (P < 0.01) redness (a* values) and yellowness (b* values) of the LM and SV. In combination with short lairage, long transport decreased (P < 0.05) pork lightness (lower L* values), and electrical conductivity was increased (P < 0.05) after long transport. Several interactions between stress level and muscle type (P < 0.001) were observed. High preslaughter stress decreased (P < 0.001) muscle glycogen in both the LM and SSP, but this decrease was greater in the LM. Lactate concentrations were increased (P < 0.001) only in the LM by high preslaughter stress. Increases in ultimate pH (P < 0.001) and decreases in a* values (P < 0.01) were greatest in the SV, whereas increases in electrical conductivity (P < 0.001) were greatest in the LM. The lack of interactions among transportation, lairage, and muscle type was attributed to the relatively minor differences in stress among treatments. It was concluded that, in glycolytic muscle types such as the LM, the high physical and psychological stress levels associated with stress in the immediate preslaughter period have a greater effect on the water-holding capacity of the meat and may promote PSE development. Conversely, oxidative muscle types tend to have higher ultimate pH values and produce DFD pork in response to intense physical activity and/or high psychological stress levels preslaughter.

Treadmill exercise is not an effective methodology for producing the dark-cutting condition in young cattle1,2

Holstein steer calves (n = 25) were used to evaluate the effects of treadmill exercise (TME) on blood metabolite status and formation of dark-cutting beef. Calves were blocked by BW (156 +/- 33.2 kg) and assigned randomly within blocks to 1 of 5 TME treatments arranged in a 2 x 2 factorial design (4 or 8 km/h for a duration of 10 or 15 min) with a nonexercised control. Venous blood was collected via indwelling jugular catheters at 10, 2, and 0 min before TME and at 2-min intervals during exercise. Nonexercised steers were placed on the treadmill but stood still for 15 min. Serum cortisol levels, as well as plasma concentrations of glucose, lactate, and NEFA, were similar (P > 0.05) before TME. Serum cortisol concentrations were unaffected (P > 0.05) during the first 6 min of TME, but between 8 and 15 min of TME, cortisol concentrations were greater (P < 0.05) in steers exercised at 8 km/h than those exercised at 4 km/h or controls (speed x time, P < 0.001). Although TME did not affect (P > 0.05) plasma glucose levels, plasma lactate concentrations in steers exercised at 8 km/h increased (P < 0.05) sharply with the onset of the TME treatment and remained elevated compared with steers exercised at 4 km/h or unexercised controls (speed x time, P < 0.001). Exercised steers had the lowest (P < 0.05) plasma NEFA concentrations during the first 6 min of TME compared with unexercised steers; however, NEFA concentrations were similar after 10 and 12 min of TME, and by the end of TME, steers exercised at 8 km/h had greater (P < 0.05) NEFA levels than nonexercised controls or steers exercised at 4 km/h (speed x time, P < 0.001). Even though muscle glycogen levels and pH decreased (P < 0.001) and muscle lactate concentrations increased (P < 0.001) with increasing time postmortem, neither treadmill speed nor TME duration altered postmortem LM metabolism. Consequently, there were no (P > 0.05) differences in the color, water-holding capacity, shear force, or incidences of dark-cutting carcasses associated with preslaughter TME. It is apparent that preslaughter TME, at the speeds and durations employed in this study, failed to alter antemortem or postmortem muscle metabolism and would not be a suitable animal model for studying the formation of the dark-cutting condition in ruminants.

Variations in meat pH of beef bulls in relation to conditions of transfer to slaughter and previous history of the animals1

Animals are subjected to various events that cause physical exhaustion and psychological stress during transfer to slaughter. This can lead to defective meat quality. Some animals may be better able to withstand the stress of transfer, depending on their previous experience of transport and on their finishing conditions (mixing, farmers' attitudes). The objective of this study was to assess the impact of 1) the conditions of transfer to slaughter (including duration of the journey, waiting time at lairage, etc.); and 2) the bulls' previous history (including experience in transport, mixing during finishing, and the farmers' attitudes) on the reactions of bulls to transfer and on their meat quality. We conducted a survey in commercial conditions. The history of the bulls and the facilities on the farms were noted; farmers were questioned on their attitudes; the bulls' reactions to loading into and unloading from the truck were observed; journey-related data were collected; and cortisol concentration at slaughter and the pH of the LM and the rectus abdominis were measured. Our study confirmed that certain physical factors associated with transport can increase stress and limit the decline of meat pH. These factors include the absence of loading facilities on the farm, transport on a warm day, or a short waiting time at lairage. Social aspects also played a role; the presence of bulls from the same finishing group limited stress and improved the pH decline. Events and management before transfer were also of importance; the farmer awareness of the sensitivity of bulls to humans or to feeding schedules but the absence of a positive attitude toward close contacts with bulls were all likely to limit stress or its consequences on meat pH. Although these results need to be confirmed in controlled experiments, they suggest that good management of beef bulls before and during transfer is essential to meat quality.

Duration of restraint and isolation stress as a model to study the dark-cutting condition in cattle1,2

Holstein steer calves (n = 32; 156 +/- 33.2 kg average BW) were used to evaluate the duration of restraint and isolation stress (RIS) on endocrine and blood metabolite status and the incidence of dark-cutting LM. Calves were blocked by BW and assigned randomly within blocks to one of four stressor treatments: unstressed controls (NS) or a single bout of RIS for 2, 4, or 6 h. Venous blood was collected via indwelling jugular catheters at 40, 20, and 0 min before stressor application and at 20-min intervals during RIS. Unstressed calves remained in their home stanchions and, except for blood sampling, were subjected to minimal handling and stress. Serum cortisol and plasma lactate concentrations were increased (P < 0.01) during the first 20 min after RIS application, and remained elevated throughout the 6 h of RIS. Plasma concentrations of glucose and insulin were greater (P < 0.05) in RIS calves than in NS calves after 80 and 100 min of stressor application, respectively; however, RIS did not (P > 0.80) affect plasma NEFA concentrations. Calves were slaughtered within 20 min of completion of RIS, and muscle samples were excised from right-side LM at 0, 0.75, 1.5, 3, 6, 12, 24, and 48 h after exsanguination for quantifying LM pH, and glycogen and lactate concentrations. The pH of the LM from calves subjected to 6 h of RIS exceeded 6.0, and was greater (P < 0.05) at 24 and 48 h postmortem than the pH of NS calves or calves subjected to 2 or 4 h RIS. Muscle glycogen concentrations did not differ (P = 0.16; 25.58, 10.41, 13.80, and 14.41 micromol/g of wet tissue weight for NS and 2-, 4-, and 6-h RIS, respectively), and LM lactate concentrations tended to be lower (P = 0.08) in calves subjected to 6 h of RIS. At 48 h after exsanguination, the LM from calves subjected to 6 h of RIS had more (P < 0.05) bound and less (P < 0.05) free moisture than did the LM from NS calves or calves subjected to 2 or 4 h of RIS. Additionally, the LM from RIS calves was darker (lower L* values; P < 0.05) than the LM of NS calves. Visual color scores for the LM were greatest (P < 0.05) for calves subjected to 6 h of RIS and least (P < 0.05) for NS calves. Subjecting lightweight Holstein calves to 6, 4, and 2 h of RIS resulted in six (75%), two (25%), and two (25%) carcasses characteristic of the dark-cutting condition, respectively. There were no dark-cutting carcasses produced from NS calves. Thus, RIS may be a reliable animal model with which to study the formation of the dark-cutting condition.

Inhibition of endogenous nitric oxide production influences ovine hindlimb metabolism independently of insulin concentrations1

The hindlimb arteriovenous difference (AVD) model was used to determine whether 30 mg/ kg of the nitric oxide synthase (NOS) inhibitor L-NGnitroarginine methyl ester (hydrochloride; L-NAME) inhibited ovine NO synthesis and influenced muscle metabolism. Eight Border Leicester x Merino cross lambs (50 to 55 kg BW) were infused with saline (control) or saline containing L-NAME via an indwelling jugular vein catheter in a balanced randomized crossover design with 3 d between treatments. The abdominal aorta and deep femoral vein were catheterized for assessment of AVD of hind limb metabolism. Arterial hematocrit and insulin concentration and both arterial and venous concentrations of nitrate/nitrite (NOx), glucose, lactate, NEFA, and urea were determined. Infusion of L-NAME decreased arterial NOx concentrations (P = 0.049), indicating inhibition of systemic NO synthesis. Treatment had no effect on arterial (3.5 vs. 3.6 +/- 0.19 mmol/L for control and L-NAME lambs, respectively; P = 0.39) or venous (3.3 vs. 3.4 +/- 0.16 mmol/L, P = 0.55) plasma glucose concentrations or on glucose AVD (0.19 vs. 0.27 +/- 0.065 mmol/L, P = 0.20). There was an interaction (P = 0.038) between time and treatment, such that L-NAME initially increased the AVD of glucose (up to 180 m) divergent from control lambs. The response was then decreased before a possible inflection beyond 240 min. Infusion of L-NAME increased hindlimb venous NEFA (222 vs. 272 +/- 13.2 micromol/L, P = 0.007) and NEFA AVD (79.4 vs. -13.3 +/- 31.5 micromol/L, P = 0.018). These metabolic changes were independent of plasma insulin concentrations, which were not affected by L-NAME infusion (25.3 vs. 27.8 +/- 3.62 mU/L, P = 0.85). The increase in hindlimb lipolysis after L-NAME infusion does not seem to be due to increased lipolysis of plasma triacylglycerol because circulating arterial (155 vs. 142 +/- 20.8 micromol/L, P = 0.58), venous (154 vs. 140 +/- 20.5 micromol/L, P = 0.50), and AVD (1.0 vs. 2.9 +/- 3.17 micromol/L, P = 0.38) triacylglycerol concentrations were unaffected by L-NAME infusion. In conclusion, these data indicate that infusion of 30 mg of L-NAME/kg inhibits NO synthesis, which in turn influences fat and carbohydrate metabolism in the ovine hindlimb independently of plasma insulin concentrations.

Skeletal muscle fibre characteristics in young and old bulls and metabolic response after a bullfight

Fibre type composition, activities of enzymes such as citrate synthase (CS), 3-hydroxyacyl coenzyme A dehydrogenase (HAD), lactate dehydrogenase (LDH), as well as glycogen, lactate and pH levels were analysed in muscle biopsies (m. gluteus medius) obtained after bullfighting from 10 young and 10 old bulls. No changes were seen in fibre type composition between groups, but the older bulls had higher HAD and LDH activities. Low glycogen concentrations and low pH values were found in both groups, but the lactate concentration after bullfighting was higher in the older group of bulls. The histochemical stain for glycogen revealed that type IIB fibres in both young and old bulls contained more glycogen than seen in type IIA and type I fibres. These results show that young and old bulls have similar muscle fibre type composition, but the metabolic capacity differs, with a higher glycolytic capacity and lactate production in older bulls. Furthermore, it seems that the physical and emotional stress in connection with a bullfight causes a marked depletion of glycogen, especially of type I and IIA fibres.

Glycogen depletion according to muscle and fibre types in response to dyadic encounters in pigs (Sus scrofa domesticus)--relationships with plasma epinephrine and aggressive behaviour

Changes in glycogen content according to fibre type were assessed in a predominantly white (Longissimus) and a predominantly red (Semispinalis) pig muscle, in response to dyadic encounters involving aggressive interactions. Tested animals showed significantly lower glycogen levels than the control in the Semispinalis, but not in the Longissimus muscle. Histological treatment of muscle serial cuts followed by computerized image analysis showed that the observed decrease in muscle Semispinalis glycogen level occurred only in fast-twitch fibres. Total glycogen and glycogen contents in fast-twitch fibres of the Semispinalis muscle were closely and negatively related to aggressive behaviour, but not with plasma epinephrine levels during and at the end of the encounters. The present results provide indirect evidences suggesting a major influence of fighting-induced physical activity on muscle glycogen depletion in response to aggressive interactions in pigs.