Effect of level of handling on meat quality of cattle of two breed types.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. I6 EFFECT OF LEVEL OF HANDLING ON MEAT QUALITY OF CATTLE OF TWO BREED TYPES B.L. MCINTYRE* and W.J. RYAN** SUMMARY In Phase I of this experiment, Kimberley Shorthorn steers approximately six months of age were subjected to either Experimental (intensive) or Commercial (minimal) handling treatments for a period of six months. One side of each carcase was electrically stimulated while the other remained unstimulated. In Phase II, a sample of 12 months old Kimberley Shorthorn steers remaining from Phase I and 9 months old Angus steers were subject to the same handling treatments for the next 12 months. Both sides of these carcases were electrically stimulated. Handling treatment had no significant (P < 0.05) effect on meat quality in either breed or in either Phase. In Phase I electrical stimulation had no beneficial effect on meat quality. An unusually high incidence of dark cutting meat of high ultimate pH was found in these animals. In Phase II Angus were significantly (P < 0.05) more tender than Kimberledy Shorthorns, but, after adjustment by covariance for fat thickness, this advantage was removed. (Keywords: cattle handling, muscle pH, meat quality). INTRODUCTION Procedures leading to the slaughter of cattle inevitably impose stress on the animal, the severity of which depends on factors such as the distance travelled, temperature, mixing of strange groups and temperament. (See reviews by Grandin 1980 and Lister et al. 1981). The stressors can be physical (e.g. exhaustion, illness) and psychological (fear, aggression) and can lead to a depletion in muscular energy reserves which results in high ultimate pH and dark cutting meat. In studying the effect of pH on tenderness, Bouton et al. (1983) reported a curvelinear relationship with maximum toughness in the pH range of 5.8 to 6.0. To our knowledge no information is available on the effect that previous handling may have on such stress. It is possible that animals which have been handled frequently could be less prone to stress prior to slauqhter. Our own results (Ryan and McIntyre unpublished) have shown that meat was touqher from animals raised under extensive pastoral conditions than that from animals transferred to the more intensive aqricultural areas. In addition there was a trend for tenderness to improve with increasinq time spent by animals qrazinq in agricultural areas. We therefore hypothesized that an increase in the level of handlinq improves meat quality throuqh a reduction of susceptibility to stress during the marketinq process. MATERIALS AND METHODS In Phase I, 72 Kimberley Shorthorn weaner steers of approximately six months of aqe were transferred in June 1982 by road transport from the East Kimberley pastoral area to the aqricultural areas of the South-West of Western Australia. These animals were allocated randomly from within weight strata * ** W.A. Department of Aqriculture, Baron-Hay Court, South Perth, W.A0 6151. Department of Animal Science, University of Western Australia, Nedlands, W.A. 267 Proc. Aust. Soc. Anim. Prod. Vol. 16 to three replicates of each of two handlinq treatments. Each group of 12 animals grazed a 10 ha paddock of improved pastures of subterranean clover (T. subterraneum) and ryeqrass (L. rigidum). The handlinq treatments were Experimental handling (EX); intensive handlinq, monthly yardinq for weighing and ultrasonic backfat testing, weekly inspection of stock usinq a motor vehicle and Commercial handlinq (COM); minimal handlinq, weekly inspection of stock as above , yarding only when necessary for animal husbandry procedures. Six animals from each replicate were slauqhtered in December 1982. Animals were yarded and weiqhed in the afternoon of day 1 loaded and transported by truck (approx. 140 km) on day 2, and slauqhtered on day 3. One side of each carcase was electrically stimulated (800 volts RMS; 14.3 pulses per set for 90 seconds). In Phase II, 36 weaner Angus steers (approximately nine months old) from the aqricultural areas were included in the experiment in December 1982. These animals were allocated from within weight strata to two replicates of each handling treatment. The 36 remaininq Kimberley Shorthorn steers were reallocated similarly to treatments corresponding with their previous handlinq treatment. These animals grazed until slauqhter in December 1983 and the same preslauqhter procedures applied. Both sides of these carcases were electrically stimulated. Hot carcase weight (fats out, tail off) and fat thickness at the 12th rib were measured. Carcases were hunq in a chiller for three days at 203~. Meat colour was visually assessed 45 minutes after quarterinq between the 10th and 11th ribs using reference colour photoqraphs. A sample of M. lonqissimus thoracis et lumborum posterior to the 11th rib was removed from each side of the carcase in the case of the cattle slauqhtered in December 1982 and from one side of each carcase in the followinq year. Samples were frozen at -18OC prior to quality assessments. Instron shear force and adhesion, taste panel evaluation, meat colour and pH were measured as described by McIntyre and Ryan (1984). For Phase I the data were analysed as a split plot structure with handling treatment as the main effect and post-slauqhter treatment as the sub-treatment . For Phase II, handling treatment and breed were treated as main effects. Paddock effects were removed and treatment effects tested aqainst between animal variation. Hot carcase weiqht and fat thickness were included as covariates in the analysis for Phase II. RESULTS In Phase I there was no difference in performance of the animals due to handling treatment with both qroups qaininq approximately 120 kq in 150 days (see Table 1). Animals were very lean at the time of slauqhter. Neither handlinq treatment nor electrical stimulation had any siqnificant (P < 0.05) effect on meat quality assessments of shear force, adhesion and taste panel. There was a high incidence of dark meat of hiqh ultimate pH (71 and 46 per cent above pH 5.8 and 6.0 respectively). This was not affected by handling treatment or by electrical stimulation. As shown in Table 2, the Anqus qained approximately 25 kg more than the Kimberley Shorthorns and also had greater carcase weiqht and fat thickness. There were no siqnificant (P < 0.05) differences in any of the meat quality characteristics due to handling treatment nor any siqnificant (P < 0.05) interactions. However, breed had a significant (P < 0.05) effect, with Angus having lower adhesion, hiqher taste panel score and liqhter meat colour than 268 Proc. Aust. Soc. Anim. Prod. Vol. 16 the Kimberley Shorthorns. When fat thickness was included as a covariate, only . adhesion and meat colour remained significantly (P < 0.05) different between breeds. Table 1 Live animal performance, carcase characteristics and meat quality of Kimberley Shorthorn steers slaughtered after Experimental (EX) or Commercial (COM) handling for six months (1) (2) Taste panel scores range from 1 = very tough to 6 = very tender Meat colour scores ranged from 1 = very light red to 6 = very dark Table 2 Live animal performance, carcase characteristics and meat quality of Kimberley Shorthorn (KSH) and Angus (ANG) steers slaughtered after Experimental (EX) or Commercial (COM) handlinq for 18 and 12 months respectively 269 Proc. Aust. Soc. Anim. Prod. Vol. I6 DISCUSSION The results of this handling of cattle on farm Also no reduction in level ultimate pH levels in the findings were contrary to of handling carried out in can be extrapolated to the investigation have shown that an increased level of did not result in improvements in meat quality. of susceptibility to stress was indicated from the meat from the two handling treatments. These the hypothesis. The results do sugqest that the kind experiments does not effect quality and that results commercial situation. A notable feature of the results for the Kimberley Shorthorns in Phase I was the exceptionally high incidence of dark meat with high ultimate pH. This was well above the level we have experienced in cattle of similar age from the agricultural areas. However it was consistent with results of other studies with animals of that type from the pastoral areas (Ryan and McIntyre unpublished). It seems unlikely that the low levels of muscle glycogen necessary to produce such pH levels could have been due to physical stress. Even though the animals had very low levels of fatness, both groups had gained substantial amounts of weight during the experiment and the EX group at least were still growing during the period immediately before slaughter. Although it cannot be determined from this study we suggest that the effect was due to psychological stress during the processes leading to slaughter arising as a consequence of the animal's environment in their first six months of life. Cattle raised under extensive pastoral conditions in the Kimberley have almost no contact with man so that they do not have the opportunity to lose their fear of man, his facilities and procedures, and are therefore highly sensitive in stressful situations. Even intensive handling in the initial six months in the agricultural areas was not sufficient to reduce this sensitivity to the extent that it no longer affected muscle pH. The normal pH values in the second year may indicate that the susceptibility to stress declined over time even with minimal handling. The superior meat quality of the Angus compared with the Kimberley Shorthorns in Phase II was largely accounted for by their greater fatness. It is probable that the lower connective tissue strength of the slightly younger Angus cattle (indicated by adhesion values) was also a contributing factor. The lower shear force and adhesion values of animals in Phase I compared to those in Phase II were consistent with younger animals having less connective tissue strength. The high pH in Phase I did not appear to have had a major effect on this general trend. REFERENCES BOUTON, P.E., CARROL, F.D., FISHER, A.L., HARRIS, P.V. and SHORTHOSE, W.R. (1973). J. Food Sci. a: 816. GRANDIN, T. (1980). Int. J. Stud. Anim. Prob. .& 313. LI STER, D., GREGORY , N.G. and WARRIS , P.D. (1981). In 'Deve lopments in Meat Science - 2', p. 61, ed itor R. Lawrie (Applied SC ience Publishers: London). MCINTYRE, B.L. and RYAN, W.J. (1984). Proc. Aust. Soc. Anim. Prod. u: 468. 270