Dark-cutting in muscles of the beef carcass is due to low muscle glycogen levels at slaughter and occurs particularly in autumn and winter in grass-fed cattle in southern Australia. The aim of these experiments was to investigate the effect of supplementary feeding of cattle grazing pasture during winter on muscle glycogen levels. The first experiment involved 70 cattle allocated to two stocking rates grazing improved perennial ryegrass and subterranean clover pastures [ high stocking rate ( HSR) v. low stocking rate ( LSR)] by two pasture feeding regimes ( control, pasture only v. pasture supplemented with a high-energy ration for 4 weeks) plus a feedlot treatment ( fed high-energy ration in pens with no pasture for 11 weeks). Muscle biopsies were collected from the M. semitendinosus ( ST) and M. semimembranosus ( SM) muscles and analysed for muscle glycogen. The ST muscle glycogen content for supplemented animals increased ( P < 0.05) over the feeding period but there was no effect ( P > 0.05) of supplementation on the muscle glycogen content of the SM or on the muscle glycogen content of the ST or SM of cattle in the feedlot treatment, relative to control cattle. HSR cattle tended to have lower muscle glycogen in the ST compared to LSR cattle across both feeding regimes. The second experiment used 60 cattle allocated to two treatments ( control, pasture only v. pasture supplemented with a high-energy ration for 3 weeks). The treatments were applied to cattle grazing improved perennial ryegrass and subterranean clover pastures and muscle biopsies were collected weekly from the SM and ST. Supplementation resulted in a linear increase ( P < 0.05) in muscle glycogen levels over the 3 weeks in both the SM and ST muscles. These results indicate that feed quality has a major impact on muscle glycogen levels in the SM and ST of cattle destined for slaughter. At times of the year when pasture quality is poor or quantity is lacking, supplementation with a high-energy supplement has the potential to dramatically increase muscle glycogen and reduce the incidence of dark-cutting beef.

Adrenergic activation and hormone release preslaughter is an inevitable outcome of the systems used to move cattle to slaughter. The aim of this experiment was to investigate the effects of acute preslaughter stress in beef cattle on postmortem muscle metabolism and the meat quality, including consumer-assessed eating quality. Eighty-four cattle were used on three separate days, with ‘mobs’ of four cattle allocated to either a ‘control’ (no electric goads used preslaughter) or a ‘stress’ (six prods given with an electric goad over 5–10 min) treatment at 15 min preslaughter. Cattle undergoing the ‘stress’ treatment had higher plasma lactate at slaughter. The prerigor pH and temperature, ultimate pH and temperature at rigor of the longissimus thoracis muscle were similar between treatments (P > 0.05 for all). The water-holding capacity of the longissimus lumborum was reduced by the ‘stress’ treatment, as indicated by higher levels of water lost during suspension (drip loss), storage (purge) for 21 days and cooking (cooking loss at 1 day postslaughter) (P < 0.05 for all). ‘Stress’ cattle produced longissimus lumborum muscle with similar sarcomere lengths and Warner–Bratzler shear force at 2, 6 and 21 days, compared to ‘control’ cattle (P < 0.05 for all). The longissimus lumborum muscle of cattle undergoing the ‘stress’ treatment was rated less tender, less juicy, with a less acceptable flavour, a lower ‘liking’ and a lower MQ4 score (P < 0.05 for all). The ‘bloomed’ surface colour (CIE L*, a*, b*) of the longissimus lumborum muscle at 2, 6 and 21 days postslaughter was similar between the ‘stress’ and ‘control’ treatments (P > 0.05 for all). In conclusion, cattle subjected to acute preslaughter stress using electric goads produced meat which the consumer rated as tougher with inferior quality. The inferior quality induced by the acute stress treatment was associated with reduced water-holding capacity but was independent of muscle pH and temperature.

This study was conducted to determine the effect of direct consignment compared with saleyard marketing on beef quality and palatability. A total of 258 cattle (mean carcass weight 227 ± 19 kg) from nine vendor properties in Victoria, Australia were used. From each vendor group (about 30 cattle/vendor), half were either: (1) processed through a saleyard and then sent to the abattoir or (2) directly consigned to the abattoir. All cattle were slaughtered at the same abattoir and the lairage and postslaughter management of the cattle and their carcasses was standardised. The cattle that had been directly consigned were slaughtered the day after dispatch from the property, whereas saleyard cattle were slaughtered 2 days after dispatch. Striploin (longissimus lumborum) samples were evaluated 1 day postslaughter and after 14 days aging. Overall, marketing method had only a small impact on the various meat quality measures and palatability. A significant vendor × marketing method interaction was found for most traits including muscle glycogen (semimembranosus and semitendinosus), pH (1, 3 and 24 h postslaughter), L*, a* and b* colour values and consumer panel scores [tenderness, flavour and combined score (MQ4)]. Juiciness scores were unaffected by marketing method but were significantly influenced by vendor group (P < 0.001). For MQ4 score, there was a general trend showing that steaks from cattle that had been marketed through the saleyard had marginally lower MQ4 scores than those that had been directly consigned in five of the eight groups. However, this trend was only significant for two of the five groups. A significant three-way interaction between vendor group × marketing method × aging duration was found for shear force (P < 0.001) and cooking loss percentage (P < 0.001). The effect of marketing method on shear force was generally small and not always statistically significant but there was a trend indicating that saleyard marketing resulted in slightly higher shear forces at either 1 or 14 days postslaughter for the majority of the vendor groups. It was concluded that marketing method had a small but variable impact on palatability and meat quality.

Measuring differences in the efficiency of converting feed to liveweight gains of beef cattle depends on assessments of feed intake and animal growth over a specified period. Previous studies have shown that feed intake can be measured with sufficient precision after 35 days, however, to assess growth rate with acceptable precision, a feeding period of 70 days is required when the cattle are weighed fortnightly. In order to test if more frequent weighing could improve the precision of estimates of liveweight, or reduce the duration of tests, animals were tested in units where an automatic weighing system recorded the liveweight of an animal every time it entered a feeder. Eight groups of beef bulls (171 animals in total) were tested. A random coefficient regression model including a cubic spline for time was used to estimate average daily gain. Evaluation of the residual variance, slope (average daily gain), and its standard error from the models showed that through the use of automated liveweight measurement, the duration of tests could be decreased to 56 days without reducing the precision of estimates of liveweight change. Depending on the precision required, further decreases in testing time could be accommodated.

Dark-cutting in beef carcasses is a quality and economic problem for the grass-fed beef industry in Australia, with ~10% of carcasses graded as dark-cutting. Dark-cutting results from low muscle glycogen levels at the time of slaughter. An experiment was designed to examine the relationship between season and muscle glycogen levels for cattle at pasture. Sixty steers were allocated to 2 stocking rate treatments, low and high (1.5 and 2.5 steers/ha, respectively) with 3 replicates for each treatment and grazed in 6 separate paddocks. Monthly samples of the M. semimembranosus (SM) and M. semitendinosus (ST) were taken by biopsy from all cattle and analysed for glycogen and lactate content. Significant differences in muscle glycogen were found between seasons. Average muscle glycogen levels for autumn, winter, spring and summer were 1.24, 1.00, 1.15 and 0.82 mg/g SM and 0.85, 0.91, 1.05 and 0.76 mg/g ST, respectively. The seasonal effects on muscle glycogen were not influenced by stocking rate, but it is postulated that they were influenced by nutrition, with the peak in muscle glycogen level generally coinciding with the peak in pasture quantity and quality in spring.

The feasibility of methane recovery from stored raw (RS) and anaerobically digested dairy manure slurry (DS) in covered tanks under anaerobic condition was examined. Methane (CH4) and carbon dioxide (CO2) production rate from both slurries increased significantly with storage temperature; gas production rates peaked at 35˚C. The amount of CH4 production per unit of volatile solids added of RS and DS were 0.22 and 0.14, respectively, while the respective amount of CO2 production were 0.24 L/g/day and 0.16 L/g/day. At slurry temperatures above 15˚C, the CH4 concentration of produced gas remained over 40% of the total gas.

Summary This paper discusses recent work by the authors which has investigated the nutritional regulation of glycogen concentration in skeletal muscle of sheep and cattle. Several experiments are summarised which show a clear relationship between the level of glycogen in muscle and the intake of metabolisable energy. This translates into strong seasonal effects on muscle glycogen in pasture fed cattle. The clear message is that animals destined for slaughter should be on a high plane of nutrition as this will contribute to an increased muscle glycogen at slaughter and so help alleviate the problem of dark cutting meat. Shortnterm regulation of glycogen is more problematical since the rate of glycogen repletion in skeletal muscle is relatively slow and the scope for rapid dietary change in ruminants is constrained by the need to allow rumen adaptation to high starch/sugar diets. However the sudden introduction of a high energy diet (based on cereal grain) in the presence of a erumen modifieri to reduce ruminal acidosis can increase muscle glycogen concentration within one week of feeding. The ability to further modify glycogen level in skeletal muscle using carbohydrate and electrolyte products is discussed. In particular the possibility of using oral glycerol/propylene glycol as a meaning for increasing blood glucose and so glycogen synthesis is proposed. An experiment to examine the effectiveness of MgO as a means for reducing the stress response is also discussed.

INTRODUCTION The Australian beef industry suffers from a marked seasonality of supply and variation in product quality. This poses major problems for meat processors trying to develop product branding and year round supply for both domestic and export consumers. The processors also have problems caused by underutilization of meat works for a portion of the year. In 1994 and 1995, beef exports made up 64% of Australian production. Since the liberalization of the Japanese market in 1988, there has been a shift in emphasis from the US market to the Japanese and Asian markets with a corresponding shift in emphasis towards high quality table beef. Lot feeding facilitates the production of beef all year round but has a number of problems including cost of production and competition from other exporting nations. Feedlotters also need to address a range of animal welfare and environmental issues which may affect consumer demand. There is a clear demand for high quality pasture fed beef. There is a range of markets, each with a different specification. Forward contracts for slaughter stock, which have been developed in some states, are an effective means of communicating market specifications to producers and removing some of the risk associated with “out of season” production. The work described in this contract demonstrates a range of cost effective options, based on feeding at pasture, for meeting these specifications in different production environments.

Researchers world-wide have studied feed conversion efficiency (FCE) in a range of species. The pig and poultry industry, partly through selection for FCE, have improved their competitive position against the red meat industries who have placed little direct selection pressure on their species for FCE. In pigs, selecting for increased FCE based on an ad lib. feeding system (AFCE) improves FCE, but can result in some unacceptably fat animals (Luxford, pers. comm.). Selecting for increased FCE using diets comprising only 85% of required daily intake, a scale feeding system (SFCE), produced pigs with faster genetic gain, improved FCE and leaner carcasses, compared with an AFCE feeding system (McPhee et al. 1988). Our experiment was conducted to compare the two systems as a test for FCE in cattle. Twenty-eight Hereford Angus cross steers, liveweight 349 ± 16 kg, P8 fat 4.5 ± 1.2 mm (mean ±s.d.) were randomly allocated to two treatments: ad lib. feeding (AFCE), or scale feeding (SFCE). The diet comprised a pelleted lucerne and grain based ration (15% CP, 10.7 MJ ME/kg) with 0.5 kg of straw fed daily. Each group of steers was fed one of these diets for 50 days, weighed after a 12 hour fast, then fed the other diet for 50 days. This process was repeated, so that each steer was fed each ration twice, for a total of 100 days on each treatment. This cross over design was partly to negate the effect of body composition change on FCE. The SFCE ration was calculated on 1.75% of the starting liveweight for each animal at each feeding period. The mean gross FCE of the steers was 10.1 and 11.2 kg DM/kg liveweight gain for the AFCE and SFCE diets respectively (l.s.d. 0.91kg). The P8 fat gain, measured ultrasonically, was 3.0 mm and 0.4 mm on the AFCE and the SFCE diets respectively (l.s.d. 0.8mm). Total feed intake (s.d. 60.3 kg DM) and total weight gain (s.d. 8.1kg DM) for a 50 day AFCE feeding period showed considerable variation with a significant positive correlation between these traits (r = 0.7). With SCFE the variation in intake is restricted (s.d. 23.8), but the variation in liveweight gain was still quite large (s.d. 6.2 kg) and the correlation with intake was non significant (r = 0.1) (Figure 1.)

Low voltage electrical stimulation (LV-ES) of beef carcasses is recommended to prevent the occurrence of cold-toughening of muscles, thus improving the production of tender meat (Powell et al. 1985). In a comparison of LV-ES systems, CSIRO have previously recommended that an anal probe be used as an earth for effective stimulation to occur. However, incorrect insertion of the anal probe has potential to pierce the rectal wall of the animal, which may result in increased microbial contamination. In 1 Victorian abattoir the incidence of rectal piercing is reported to be as high as 80%. This study aimed to investigate the effectiveness of alternative methods of earthing during low voltage electrical stimulation. Three methods of earthing were used to compare a Koch-Britton Low Voltage Electric Stimulator to an unstimulated control group using 30 carcasses per treatment (total = 120). Stimulation occurred within 5 minutes of slaughter with carcasses subjected to a peak voltage of 45 volts for 40 seconds at a pulse rate of three seconds on/one second off. The pH was measured in duplicate in the muscle Zungissimus dorsi, at 3 hours post-slaughter using a Sentron pH meter. Carcasses were of mixed sex and breeds and ranged from 140-250 kg hot carcase weight. The mean pH for each treatment group is shown below in table 1.