D. M. Ferguson

Have we underestimated the impact of pre-slaughter stress on meat quality in ruminants?

Stress is the inevitable consequence of the process of transferring animals from farm to slaughter. The effects of chronic stress on muscle glycogen depletion and the consequent dark cutting condition have been well documented. However, there has been little examination of the consequences of acute stress immediately pre-slaughter on ruminant meat quality. New evidence is emerging to show that non pH-mediated effects on meat quality can occur through pre-slaughter stress in cattle and sheep. This paper reviews the general aspects of pre-slaughter stress in the pre-slaughter context. It then examines the impacts of pre-slaughter stressors on ruminant carcass and meat quality and considers remedial strategies for remediating and preventing pre-slaughter stress. Further quantification of the biological costs of pre-slaughter stress and the consequences to meat quality is required.

Genetic and environmental effects on meat quality

In order for livestock industries to consistently produce high quality meat, there must be an understanding of the factors that cause quality to vary, as well as the contribution of genetics. A brief overview of meat tenderness is presented to understand how genotype and environment may interact to influence this trait. Essentially, meat tenderness is determined from the contribution of connective tissue, sarcomere length determined pre-rigor and rate of proteolysis during ageing, as well as contributions from intramuscular fat and post-mortem energy metabolism. The influence of mutations in myostatin, the callipyge gene, the Carwell or rib eye muscle gene as well as the calpain system on meat tenderness is presented. Specific examples of interactions between the production or processing environment and genetics are presented for both sheep and cattle. The day-to-day variation in tenderness is evident across experiments and this variation needs to be controlled in order to consistently produce tender meat.

Methods used in the CRC program for the determination of carcass yield and beef quality

This paper describes the methodology used for the collection of carcass yield and meat quality data from straightbred and crossbred cattle in the Cooperative Research Centre for Cattle and Beef Quality core program.

Cattle temperament: Persistence of assessments and associations with productivity, efficiency, carcass and meat quality traits

Relationships between temperament and a range of performance, carcass, and meat quality traits in young cattle were studied in 2 experiments conducted in New South Wales (NSW) and Western Australia (WA), Australia. In both experiments, growth rates of cattle were assessed during backgrounding on pasture and grain finishing in a feedlot. Carcass and objective meat quality characteristics were measured after slaughter. Feed intake and efficiency during grain finishing were also determined in NSW. Brahman (n = 82 steers and 82 heifers) and Angus (n = 25 steers and 24 heifers) cattle were used in the NSW experiment. In NSW, temperament was assessed by measuring flight speed [FS, m/s on exit from the chute (crush)] on 14 occasions, and by assessing agitation score during confinement in the crush (CS; 1 = calm to 5 = highly agitated) on 17 occasions over the course of the experiment. Brahman (n = 173) and Angus (n = 20) steers were used in the WA experiment. In WA, temperament was assessed by measuring FS on 2 occasions during backgrounding and on 2 occasions during grain feeding. At both sites, a hormonal growth promotant (Revalor-H, Virbac, Milperra, New South Wales, Australia) was applied to one-half of the cattle at feedlot entry, and the Brahman cattle were polymorphic for 2 calpain-system markers for beef tenderness. Temperament was not related (most P > 0.05) to tenderness gene marker status in Brahman cattle and was not (all P > 0.26) modified by the growth promotant treatment in either breed. The Brahman cattle had greater individual variation in, and greater correlations within and between, repeated assessments of FS and CS than did the Angus cattle. Correlations for repeated measures of FS were greater than for repeated assessments of CS, and the strength of correlations for both declined over time. Average FS or CS for each experiment and location (NSW or WA × backgrounding or finishing) were more highly correlated than individual measurements, indicating that the average values were a more reliable assessment of cattle temperament than any single measure. In Brahman cattle, increased average FS and CS were associated with significant (P < 0.05) reductions in backgrounding and feedlot growth rates, feed intake and time spent eating, carcass weight, and objective measures of meat quality. In Angus cattle, the associations between temperament and growth rates, feed intake, and carcass traits were weaker than in Brahmans, although the strength of relationships with meat quality were similar.

Factors affecting beef palatability — farmgate to chilled carcass

The potential eating quality of beef is set by the intrinsic structural and compositional characteristics of muscle. However, the extrinsic factors that prevail during the production of the animal, slaughter and processing of its carcass and finally, cooking can produce changes in these structural and compositional characteristics that ultimately manifest as large variations in beef palatability. The conditions that apply in the 24-48 h immediately before and after slaughter are recognised as having the largest influence on beef palatability. This review specifically examines the critical pre- and post-slaughter factors and discusses their putative effects on biochemical and physical changes in muscle and the consequences to beef palatability. Areas for future research within this domain are also discussed.

Genetic and phenotypic characterisation of animal, carcass, and meat quality traits from temperate and tropically adapted beef breeds. 4. Correlations among animal, carcass, and meat quality traits *

Beef cattle data from temperate (TEMP, n = 3947) and tropically adapted (TROP, n = 4137) breeds were analysed to compute estimates of genetic and phenotypic correlations between animal, abattoir carcass, and meat quality measures. Live animal traits included: liveweight (S2LWT), scanned subcutaneous rump fat depth (S2P8), scanned eye muscle area (S2EMA), flight time (S1FT), and finishing average daily gain (FADG). Carcass traits included: hot carcass weight (CWT), retail beef yield percentage (RBY), intramuscular fat percentage (IMF), subcutaneous rump fat depth (P8), eye muscle length by width (ELW), and meat colour score (MEATC). Meat quality measures taken on 2 muscles (M. longissimus thoracis et lumborum (LTL) and M. semitendinosus (ST)) included: shear force of LTL (LTL_SF) and ST (ST_SF); compression of the ST (ST_C); cooking loss % of the LTL (LTL_CL%) and ST (ST_CL%); Minolta LTL L* (LTL_L*), a* (LTL_a*), ST a* (ST_a*); and consumer-assessed LTL tenderness score (LTL_TEND). Genetic and phenotypic correlations between animal measures and related carcass traits were moderate to very high for TEMP and TROP. Genetic correlations between S2LWT and CWT were 0.89 and 0.82, between S2P8 and P8 0.80 and 0.88, and between S2EMA and ELW 0.62 and 0.68, for TEMP and TROP, respectively. Genetic correlations between animal measures and other carcass traits varied; moderate genetic correlations were estimated between S2P8 and RBY (-0.57, -0.19 for TEMP, TROP) and S2P8 and IMF (0.39, 0.23 for TEMP, TROP). Genetic correlations between animal and meat quality measures were moderate to low. For TEMP, moderate genetic correlations were estimated between S2P8 and LTL_TEND (0.38), FADG and ST_a* (-0.49), and FADG and LTL_TEND (0.45); and for TROP, S1FT and LTL_SF (-0.54), and S2EMA and LTL_L* (-0.46). Phenotypic correlations between animal and meat quality were generally low and close to zero. Several moderate to high genetic correlations existed between carcass and meat quality traits. In general, fatness measures were genetically correlated with tenderness (e.g. IMF and LTL_TEND 0.61, 0.31 for TEMP, TROP). CWT was genetically correlated with meat colour (CWT and LTL_L* 0.66, 0.60 for TEMP, TROP) and objective tenderness measures (CWT and ST_C -0.52, -0.22 for TEMP, TROP). Once again phenotypic correlations between carcass and meat quality were low, indicating that few phenotypic predictors of meat quality traits were identified. Several of the genetic correlations show that both animal and abattoir carcass traits may be of use as indirect measures for carcass and meat quality traits in multiple trait genetic evaluation systems. A , q s i A. Re Additional keywords: beef, carcass quality, genetic correlation, phenotypic correlation.

Genetics of flight time and other measures of temperament and their value as selection criteria for improving meat quality traits in tropically adapted breeds of beef cattle

Flight time, an objective measure of temperament, was recorded in 3594 Brahman, Belmont Red, and Santa Gertrudis heifers and steers. Two subjective measures of temperament (crush score and flight speed score) were also available for over 2000 of these animals. Temperament measures were recorded post-weaning (average age 8 months) and again at the start of finishing (average age 19 months) on a subset of the animals. Nine meat quality traits were measured on these animals and included measures on 2 different muscles [M. longissimus thoracis et lumborum (LTL) and M. semitendinosus (ST)]. The heritability of flight time measured post-weaning and at the start of finishing was 0.30 and 0.34, respectively, with a repeatability of 0.46 across the measurement times. Heritabilities for scored temperament traits were 0.21, 0.19, and 0.15 for post-weaning flight speed score, post-weaning crush score, and start of finishing crush score, respectively. Genetic correlations across measurement times for flight time were 0.98 and 0.96 for crush score, indicating a strong underlying genetic basis of these temperament measures over time; however, the corresponding phenotypic correlations were lower (0.48 and 0.37, respectively). Longer flight times (i.e. better temperament) were genetically correlated with improved tenderness (i.e. lower shear force and higher tenderness scores), with genetic correlations of –0.42 and 0.33 between LTL shear force, and Meat Standards Australia (MSA) tenderness, respectively. Genetic correlations between post-weaning crush score and the same meat quality traits were 0.39 and –0.47, respectively. However, genetic and phenotypic correlations between measures of temperament and other meat quality traits were generally low, with the exception of crush scores with LTL Minolta a* value (–0.37 and –0.63 for post-weaning and start of finishing measurement time, respectively). Predicted correlated responses of –0.17 kg LTL shear force and 2.6 MSA tenderness points per generation were predicted based on the genetic parameter estimates and a recording regime of both flight time and crush scores. Selection based on the measures of temperament described in this study could be used to improve temperament itself and correlated improvements can also occur in meat tenderness and eating quality traits in tropically adapted breeds of cattle.

Effect of electrical stimulation on protease activity and tenderness of M. longissimus from cattle with different proportions of Bos indicus content

The effect of electrical stimulation on protease activity (at approx. 3 h postmortem), sensory tenderness scores and shear force was determined on M. longissimus samples from three Bos indicus genotypes (0% Hereford, 50% Brahman×Hereford and 100% Brahman). The samples were divided and aged for 1 or 30 days. Electrical stimulation resulted in a general reduction in calpastatin activity suggesting that it accelerated proteolysis. Calpastatin activity increased commensurate with increasing Bos indicus content. Several significant interactions were shown, the most relevant of these was the interaction between Bos indicus content×electrical stimulation. In contrast to the other genotypes, calpain I and calpain II activities were shown to increase (significant for calpain II only) following stimulation in the purebred Brahmans (100%). There was a significant reduction in tenderness with increasing Bos indicus content. However, breed differences in shear force were reduced by electrical stimulation. The improvement in shear force following ageing was smaller for stimulated carcasses compared to the controls. This tends to reinforce the premise that electrical stimulation accelerates proteolysis. The results of this study show clear genotypic differences in proteolytic activity and tenderness. However, electrical stimulation can be employed to reduce breed differences in tenderness of the M. longissimus.

Acute stress induced by the preslaughter use of electric prodders causes tougher beef meat

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). 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.

Temperament and hypothalamic-pituitary-adrenal axis function are related and combine to affect growth, efficiency, carcass, and meat quality traits in Brahman steers.

Associations between temperament, stress physiology, and productivity were studied in yearling Brahman steers (n = 81). Steers differed in calpain system gene marker status; 41 were implanted with a hormonal growth promotant at feedlot entry. Temperament was assessed with repeated measurements of flight speed (FS) and crush score (CS) during 6 mo of backgrounding at pasture and 117 d of grain finishing. Adrenal responsiveness was assessed with ACTH challenge, with plasma samples collected immediately before and 60 min after challenge. Steers with higher FS and CS had higher prechallenge plasma cortisol, glucose, lactate, and nonesterified fatty acid concentrations. The ACTH-induced cortisol response was unrelated to FS or CS, but glucose remained higher after challenge in flightier steers. The hormonal growth promotant reduced adrenal responsiveness; tenderness genotype had no effect. When temperament assessments and cortisol concentrations before and after challenge were combined in a principal components analysis, four vectors accounting for 38%, 25%, 18%, and 9% of the variation were identified. The first vector had significant loadings on temperament and prechallenge cortisol; increasing scores were associated with increased plasma glucose, lactate, and nonesterified fatty acid and with reductions in BW and feedlot growth rates, carcass fatness, and muscle pH. The second vector loaded only on ACTH-induced cortisol response; increased scores related to increased residual feed intake, number of daily feed sessions, and meat marbling score. The third and fourth vectors had different loadings on FS and CS and appeared to identify different aspects of temperament measured by FS or CS. Fewer associations were found between the third or fourth vectors and productivity traits, possibly because of lower variance accounted for by these vectors. In conclusion, temperament was related to prechallenge cortisol but not to ACTH-induced cortisol response. Principal components analysis separated these traits into separate components, which in turn had different relations with productivity traits. The largest component of temperament was described similarly by FS and CS, but there were smaller components that these described differently. There were some temperament-related differences in the metabolic status of the steers which were not related to the variation in cortisol, suggesting involvement of the sympatho-adrenal-medullary axis in these temperament-related effects.