Some recent advances and future priorities in research for the meat industry.

The meat industry is undergoing a period of very mixed fortunes with beef in particular losing market share; however, longer term forecasts are good for all meat species with demand growth coming mainly from developing countries. This review deals in particular with the main problems that are responsible for the decline of beef as a consumer product in developed markets. These are the meat safety crisis and the unreliability of meat eating quality, especially tenderness. The review suggests that recent research has defined and clarified these problems but they have not been elucidated to the extent that is needed for product assurance. Hence, meat safety and consistent quality are two of the core issues to be addressed in future research. The third core issue is product development which is very active in the most competitive sectors of the food industry and is weak in the red meat sector.

Carcass and meat quality of finishing Friesian steers fed the ß-adrenergic agonist L-644,969.

The effect of the ß-adrenergic agonist L-644,969 on selected parameters of carcass and meat quality was examined in Friesian steers. Four groups of 18 steers were individually offered ad libitum a pelleted diet that contained 0, 0·25, 1·0, or 4·0 ppm L-644,969 for 12 weeks prior to slaughter. L-644,969 quadratically increased carcass weight (3·7, 9·3, and 8·5%, P < 0·001) and altered the distribution of lean meat such that a greater (0·3-5%; P < 0·01) proportion was in the more valuable cuts. There were no effects of L-644,969 on carcass-chill loss and on the water-holding capacity of the longissimus thoracis et lumborum (LTL) muscle. The intramuscular-fat concentration of the LTL was decreased (27-50%; P < 0·01) and the effects on muscle ultimate pH were small and commercially unimportant. Fibre-optic-probe measurements of the LTL indicated darker (P < 0·01) meat due to ß-agonist treatment. L-644,969 increased the shear force required to cut through cooked muscle from the LTL (159%, 209%, and 217%, P < 0·001). It is concluded that L-644,969 treatment improved the quantity and distribution of lean in the carcass but impaired meat quality, primarily through a reduction in tenderness.

Long-term effects of cimaterol in Friesian steers: II. Carcass composition and meat quality.

The objectives of this study were to examine the effects of long-term administration of cimaterol to steers from 4 wk of age until slaughter at target live weights of 275, 375, and 475 kg on 1) carcass composition; 2) distribution and growth of the dissectible lean, fat, and bone; and 3) selected meat quality traits. Ninety calves were allocated to either control or cimaterol (4 ppm) treatment with 15 from each treatment scheduled for slaughter at the above target live weights. Of the 90 calves, 73 carcasses were dissected. Cimaterol increased the proportion of lean in the carcass of the three target slaughter groups from 653, 629, and 612 g/kg in control steers to 728, 728, and 723 g/kg in treated steers, respectively, and decreased the proportion of fat from 134, 169, and 197 g/kg in control steers to 88, 86, and 99 g/kg in treated steers, respectively. Cimaterol increased the longissimus muscle area from 46.4, 56.7, and 62.4 cm2 in control steers to 61.0, 73.4, and 90.8 cm2 in treated steers in the three target slaughter groups, respectively. The allometric growth coefficients for total lean, bone, and fat were .987, .869, and 1.406, respectively, for treated animals and .898, .771, and 1.654, respectively, for control animals. Cimaterol increased the 2-d drip loss and the fiber-optic probe value of longissimus muscle. Shear force values were 55, 145, and 118% higher in the treated animals in the three target slaughter groups, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of pre-slaughter showering and post-slaughter rapid chilling on meat quality in intact pork sides.

Thirty pairs of Landrace or Large White pigs were used to determine the effects of pre- and post-slaughter cooling treatments on pork quality and yield. One animal from each pair was showered in cold water and after slaughter one side from each carcass was rapidly chilled and the other side was conventionally chilled. Two experiments were carried out in winter: they examined different times of exposure to cooling treatments; a further experiment was carried out in summer time. Showering caused a reduction in the temperature of the deep loin at 40 min post mortem (P < 0·01). Rapid chilling caused a further reduction in carcass temperature and the rate of pH fall was lower (P < 0·05) in the rapidly chilled sides. There was a strong indication that showering in the winter time lowered drip loss in slices of Longissimus dorsi muscle (P = 0·077) whereas showering in the summer time was not effective. Shower water temperature may have been important in this regard. Showering did not lower drip loss in intact pork legs. Rapid chilling was not effective in lowering drip loss in either slices of Longissimus dorsi or intact pork legs. Rapid chilling at -20°C for 3 h without an air blast lowered evaporative chill losses in sides of pork by 27-29% (P < 0·1) compared to normal chilling. Reduced treatments gave reduced effects. Neither treatment had any significant effect on cooking loss or toughness in broiled slices of pork Longissimus dorsi muscle.

The effect of oestrus behaviour on muscle glycogen concentration and dark-cutting in beef heifers.

Preliminary observations at an abattoir showed an association between oestrus behaviour and dark-cutting in beef. Two follow-up experiments examined the relationship between oestrus behaviour and muscle glycogen content, carcass bruising and meat ultimate pH. In the first experiment heifers in oestrus were compared with controls in mid-cycle. Oestrus was associated with a loss of glycogen in M. longissimus dorsi. Also plasma creatine kinase activity increased, reflecting bruising or strenuous muscle activity. In the second experiment heifers were slaughtered during oestrus. On the basis of pre-slaughter behaviour they were assigned to active or inactive groups, which subsequently yielded 39% and zero dark-cutting carcasses, respectively. Loss of muscle glycogen was accounted for by the number of times an animal mounted (r = -0·85). Likewise, variation in meat ultimate pH was associated with mounting activity (P < 0·001). Carcass bruising was higher in the active group (P < 0·0.001) and the main cause of bruising was being mounted (r = 0·74). It was concluded that single penning of oestrus heifers to eliminate mounting activity would reduce the incidence of dark-cutting.

The effect of stocking density during 4 hour transport to slaughter on behaviour, blood constituents and carcass bruising in Friesian steers.

The aim of this work was to assess the response of Friesian steers to road transportation at low, medium and high (ca 200, 300 and 600 kg/m(2)) stocking densities in terms of physiology, behaviour and carcass bruising. Stocking density was determined by adjusting the number of animals per pen (3 runs) or by adjusting pen size (3 runs). Plasma cortisol and glucose increased (P < 0·001) with stocking density, as did plasma CK activity (P < 0·001) and carcass bruising (P < 0·01) both of which indicate muscle damage. At constant stocking density stress increased with pen location towards the tail of the truck, as reflected by a significant increase in plasma cortisol. Stocking density influenced standing orientation within the truck. At low stocking density animal movement was unrestricted and the preferred orientation was standing parallel to the direction of travel; there was a strong bias against diagonal orientations. Losses of balance were associated with specific driving events, notably braking and cornering. Minor losses of balance were observed at all stocking densities, but major losses of balance including animals going down underfoot were associated with high density. When an animal went down at high stocking density it did so involuntarily and was sometimes trapped down, destabilizing other members of the group in a domino effect. Exploratory, sexual and aggressive behaviours were inhibited at high stocking density, with the exception of mounting and pushing, which increased in frequency with stocking density. It was concluded that the high stocking density adversely affected animal welfare and lowered carcass quality when compared with the medium and low stocking densities.

Evaluation of some objective methods for measuring pork quality.

Several objective methods for estimating pork quality were evaluated, by correlating instrument values against visual scores by an experienced panel. The measurements examined were reflectance, fibre optic probe, pH, drip and Kapillarvolumeter values. Measurements were made on intact carcasses or after cutting across at the shoulder, mid-loin and ham. In chilled pork cuts, the fibre optic probe (FOP(u) value) and reflectometer agreed most closely with panel scores (r = 0·71 and 0·78, respectively). The probe has the added advantage of providing a useful indication of meat quality in the uncut carcass. Drip loss was about equally correlated with FOP(u), reflectance and Kapillarvolumeter values (r = 0·7 in all cases). In hot carcasses, the fibre optic probe (FOP(l) value) was superior to the pH(l) value for predicting panel score (r = 0·76 and -0·53 respectively) and reflectance (r = 0·80 and -0·60), whereas pH(l) was better than FOP(l) for predicting drip loss (r = -0·65 and 0·55).

Glycogen depletion patterns in myofibres of cattle during stress.

The response of the three major types of fibre in beef M. longissimus dorsi during stress and recovery was examined with respect to cellular glycogen content. Two different forms of stress were induced in Friesian bulls, by mixing with strangers for a 5h period or by subcutaneous injections of adrenaline. Muscle biopsy samples were taken during stress and recovery for biochemical and histochemical analysis of glycogen content. Muscle glycogen concentration fell to 45% of the resting value during mixing stress and to 37% of the resting value after adrenaline treatment. Slow-twitch and fast-twitch fibre types responded differently to stress, and the differences were reversed in the two forms of stress studied. Mixing stress caused a greater loss of glycogen from the two fast fibre types than from the slow type while adrenaline caused a much greater loss of glycogen from the slow fibres than from the two fast fibre types. The results demonstrate that glycogen is selectively depleted in muscle fibres in response to stress and that the pattern of depletion is different in adrenaline versus mixing stress.

Glycogen content and repletion rates in beef muscle, effect of feeding and fasting.

The effect of type of diet and fasting on resting muscle glycogen concentration and on rate of recovery after glycogen depletion was studied in beef M. logissimus dorsi. Hereford heifers were fed either barley or hay, or were fasted for 9 days. Resting muscle glycogen concentration was significantly increased by feeding barley and decreased by fasting, relative to the value in cattle on a maintenance diet of hay. Rates of repletion of muscle glycogen following depletion by adrenalin injection averaged 7.6 mumol/g per day on barley, 6.1 mumol/g per day on hay and 1.5 mumol/g per day in fasted heifers. On refeeding the fasted group with hay the rate of glycogen reported for nonruminant species. The specific activity of muscle glycogen synthase (I + D) was 2.13 mumol/minute per gram of wet tissue, and normal conversion to the active (I) form was observed in glycogen-depleted beef muscles. Determination of blood glucose, plasma insulin and muscle glucose 6-phosphate concentrations provided some evidence for a decreased availability of glycogen precursors during the period of muscle glycogen resynthesis. It was concluded that a lower glucose availability in cattle compared with nonruminant species caused a slower rate of muscle glycogen repletion. Different repletion rates between the experimental groups reflected different levels of energy intake and corresponding changes in glucose utilization rates.

Behavioral stress and skeletal muscle glycogen metabolism in young bulls.

Friesian bulls were penned with an established group of bulls for 6 h. This mixing procedure normally resulted in an intense behavioral interaction between the established herd and each of the newly introduced experimental animals. Muscle needle biopsy samples and blood samples were taken before stress and at intervals during the recovery period. Stressed bulls showed increases over controls in body temperature (P less than .001), heart rate (P less than .001), serum nonesterified fatty acids (P less than .05) and plasma creatine kinase (P less than .01). Muscle glycogen content fell during stress to 41% of the value for the control animals (P less than .001). On the first day of the recovery period, the glycogen content increased slightly, to 45% of the mean control value, and on d 2 it increased substantially, to 70%. A significant difference existed between experimental and control groups until d 7 of the recovery period. Blood glucose did not differ significantly between the control and experimental groups immediately after stress or during the recovery period. Muscle glucose-6-phosphate was lower in the experimental animals immediately after stress (P less than .01) and also on d 1 of recovery (P less than .05). Plasma immunoreactive insulin remained close to 40 microunits/ml in both groups, except on the day after stress, when it was below (P less than .05) the prestress value. The results show that substantial muscle glycogen breakdown occurred during the period of behavioral stress and that recovery to resting values was a comparatively slow process. It was concluded that the inherently lower blood glucose concentration and insulin activity in cattle than in nonruminant species may reduce glucose availability in cattle and thereby delay muscle glycogen recovery.

An investigation of ultimate pH in the muscles of commercial beef carcasses.

Ultimate pH values were recorded in the carcasses of steers and heifers at a beef slaughtering plant over a period of 3 years. The incidence of carcasses with a pH(u) ≥ 6·0 in the LD-a value usually associated with 'dark-cutting' in beef-was 3·2%. A pronounced seasonal effect was observed with the incidence rising from 1·2% for the period February to August to 5·2% for the period September to January, inclusive. An examination of thirteen muscles showed that increases in pH(u) above normal values occurred most frequently in the LD and four large muscles of the hindquarter and were much less frequently observed in the eight other hind- and forequarter muscles examined. In the carcasses of young bulls, also slaughtered under commercial conditions, high pH(u) values were predominantly associated with the same muscles as in steers and heifers. However, when experimental cattle were given adrenaline to induced high pH(u) values, this treatment resulted in a general increase in pH(u) in all the muscles examined. The different pattern of pH(u) elevation in the adrenaline-treated and commercial carcasses suggests different physiological mechanisms in the two cases.

The effect of skeletal muscle needle biopsy on blood constituents, muscle glycogen and heart rate of cattle.

Muscle samples from Friesian bulls were obtained using the Bergström percutaneous biopsy needle. The samples (100 to 200 mg) were suitable for metabolite and enzymic analyses and histological examination in relation to meat quality. The physiological response to biopsy was assessed by measuring serum free fatty acid and blood glucose concentrations, plasma creatine kinase activity and heart rate. Muscle glycogen concentration was also measured. These parameters were unchanged by the experimental procedure, with the exception of blood glucose and heart rate which showed significant increases. The experimental animals showed no adverse effects after repeated biopsy and it is concluded that the technique is suitable for investigating beef muscle metabolism in vivo, and does not cause an unacceptable degree of stress.