Variation in butt shape of carcasses of British cross and Brahman cross cattle slaughtered for domestic consumption.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 19 VARIATION IN BUTT SHAPE OF CARCASSES OF BRITISH-CROSS AND BRAHMANCROSS CATTLE SLAUGHTERED FOR DOMESTIC CONSUMPTION G. A. ELDRIDGE and C. I. BALL Victorian Institute of Animal Science, Dept of Food and Agriculture, Werribee, Vic. 3030. SUMMARY The butt shape of carcasses from 136 Brahman-cross and 135 British-cross cattle that were slaughtered for the domestic market were compared by objective measurement of their lateral and dorsal profiles using video image analysis (VIA). The carcasses from British-cross cattle were significantly (P < 0.01) lighter, leaner and shorter in length than the Brahman-cross cattle. VIA measurements of the butt of the carcasses from both types of cattle were significantly (P c 0.001) correlated with hot standard carcass weight and eye muscle area but only the VIA measurements from Brahman-cross carcasses were significantly correlated with fat depth at the P8 site. VIA dimensions of the butt profiles from Brahman-cross cattle, standardised for variation in carcass weight, had significantly (P < 0.01) greater lateral and smaller dorsal dimensions than British-cross cattle but there was no difference between genotypes in the cross-sectional areas of the butts. It was concluded that any subjective or objective appraisal of butt shape to assess carcass value should consider both the lateral and dorsal profiles of the butt and that fatness of the carcass needs to be considered. Keywords: cattle, carcass measurement, carcass assessment. INTRODUCTION A descriptive language to describe carcass and meat attributes has been developed by AUS-MEAT to assist in the marketing of Australian beef and improve productive efficiency by providing feed-back to producers. AUS-MEAT, which is the authority for uniform specification of meat and livestock, uses carcass weight, fatness, dentition, sex, bruising and a butt shape score, which is subjectively assessed from the lateral profile of the butt, to describe beef carcasses. However, considerable controversy surrounds the use of this butt shape score to describe differences in carcass value. While a butt shape or profile score is used to assess carcass meat yield in Europe (Wood 1989) and in New Zealand (Butler-Hogg and Kirton 1989), there is a lack of consensus on the value of using butt shape score to assess carcass value in Australia. The differences of opinion on the value of butt shape may be due to current techniques used to score butt shape and/or differences in the genotypes of cattle used for beef production in Australia. This paper compares the butt shape of carcasses from Britishcross and Brahman-cross cattle slaughtered for domestic consumption by measurement of butt dimensions by video image analysis (VIA). MATERALS AND METHODS Groups of 136 Brahman-cross and 135 British-cross cattle destined for the domestic meat market were slaughtered at Rockhampton, Queensland during April 1988 and at Scone, New South Wales during November 1988, respectively. Following trimming, the lateral and dorsal profiles of the right side of each carcass were recorded on video tape by a video camera mounted 1 m below the hangingrail and 34 m from the carcass. A sight-board was suspended from the hanging-rail at the beginning of each recording session for calibration of measurements by VIA. Each carcass was measured for total body length (BDYLTH) from the hook to the 1st thoracic vertebra and for carcass length (CASLTH) from the 1st sacral to the 1 st thoracic vertebra inclusively using a carcass measuring rod. The carcasses were weighed after dressing to AUS-MEAT standards to obtain a hot standard carcass weight (HSCW). Fat depth was measured at the P8 site (FATP8) which is lateral to the dorsal spines at the highest point of the sacral crest and in line with the sacro-tuberous ligament at its attachment to the dorsal tuberosity of the tuber ischii. FATP8 was measured using a Hennessy Grading Probe at Rockhampton and by cut and measure at Scone. Each carcass was divided at the 12-13th rib and measurements of the cross-sectional area of the M. longissimus dorsi (eye muscle) were obtained by tracing the outline of the eye muscle onto an acetate sheet and subsequently calculating eye muscle area (EMA) using a planimeter. The measurements made by VIA of the lateral and dorsal butt dimensions defined as L30, L40, L50, D30, D40 and D50 respectively are shown Fig. 1 and were made on an IBM compatible computer using a Data Translation image analysis board DT2853 which counts dimensions in pixels. The pixels were converted into mm by using the dimensions of the sight-board for calibration at each recording session. 61 Proc. Aust. Sot. Anim. Prod. Vol. 19 The lateral and dorsal profile measurements of the butt were used to compute the cross-sectional area of the butt at each VIA measurement point and defined as AR30, AR40 and AR50. VIA measurements together with the carcass measurements BDYLTH and CASLTH were standardised by 1/(HSCW)0.33 for variation in carcass weight for statistical analysis of butt shape between the 2 genotypes. Fig. 1. Diagrammatic representation of the lateral profile (L30, L40 and L50) and the dorsal profile (D30, D40 and D50) sites measured by video image analysis (VIA). RESULTS Although the ages of animals in this study were unknown most British-cross cattle had teeth and ranged from O-2 permanent incisors while most Brahman-cross cattle had 8 incisors and ranged from O-8 teeth (mean 6.9 teeth). The carcasses from the British-cross significantly (P < 0.01) lighter, leaner and had significantly (P < 0.01) larger EMA' than the s cross animals while the BDYLTH and CASLTH of Brahman-cross cattle were significantly greater than the British-cross cattle (Table 1). deciduous permanent cattle were Brahman(P < 0.01) Table 1. Hot standard carcass weight (HSCW), P8 fat depth (FATP8), eye muscle area (EMA), body length (BDYLTH) and total length (CASLTH) of carcasses for British-cross (n=136) and Brahman-cross (12=137) cattle The VIA measurements of butt dimensions from carcasses from British-cross and Brahman-cross cattle were significantly (P < 0.001 and P < 0.01) correlated with HSCW and EMA (Table 2). Although VIA measurement of the butt dimensions of carcasses from Brahman-cross cattle were significantly (P < 0.05 and P < 0.01) correlated to FATPS (Table 2), there was no relationship between VIA shape dimensions and FATP8 from British-cross cattle. Using dimensions of butt shape of carcasses standardised for variation in HSCW (1/(HSCW)0*33), the lateral VIA dimensions of the butt of carcasses from B&man-cross cattle were significantly (P < 0.05 and P < 0.01) greater than the equivalent VIA dimensions of the carcasses from the British-cross cattle 62 Proc. Aust. Sot. Anim. Prod. Vol. 19 Table 2. Correlation co-effkients (r) between hot standard carcass weight (HSCW), fat depth at the P8 (FATP8) and eye muscle area (EMA) and VIA measurements of butt profues of British-cross (n=135) and Brahman-cross (n=136) carcasses Table 3. Variation in VIA measurements of butt profiles standardised for variation in HSCW (l/HSCWo33) and cross-sectional areas (AR30, AR40 and AR50) estimated from VIA butt profile measurements made on carcasses from British-cross and Brahman-cross cattle while the dorsal VIA dimensions of the carcasses of British-cross cattle were significantly P < 0.01) _>yreater than those of the Brahman-cross cattle (Table 3). The computed cross-section areas from the VIA lateral and dorsal dimensions of the carcasses from the 2 groups of cattle were not significantly (P > 0.05) different (Table 3). DISCUSSION The significant differences between the lateral and dorsal VIA dimensions of butt profiles of Brahman and British-cross cattle (Table 3) indicate that the 2 genotypes are markedly different in butt shape. Although the lateral and dorsal measurements of butt profiles from Brahman-cross carcasses were greater and smaller than the respective measurements from carcasses of British-cross cattle, there was no difference in the computed cross-sectional area between the genotypes. Consequently, it is suggested that although butt shape may vary significantly, there may be no difference in muscularity of the butt between genotypes. These results also indicate that any assessment of butt shape score using a single profile could result in scores that either over or under estimate carcass value for the different genotypes. As could be expected, VIA measurements of butt dimensions are significantly correlated with HSCW and reflect the physical size of the carcass (Table 2), however standardisation of these dimensions for variation in carcass weight allows VIA to be used as an objective assessor of butt shape. The significant correlation (Table 1) between VIA butt shape measurement of the Brahman-cross and 63 Proc. Aust. Sot. Anim. Prod. Vol. I9 FATP8 indicate however, that carcass fatness is reflected in butt shape for at least this class of stock and may need to be considered in any objective VIA assessment of butt shape. The highly significant correlations between VIA measurement and EMA (Table 2) suggests that VIA could be used (possibly in conjunction with other indicators) to assess EMA in the intact carcass. The marked differences in correlation coefficients and the significant difference in EMA (Table 1) between the 2 genotypes suggests that some other factors, for example, carcass fatness and / or carcass length may be involved in such a relationship. The results of this study also indicate that when sold for the domestic market, Brahman-cross cattle from northern Australia are, in general, considerably older and have a larger skeletal structure than British-cross cattle with a similar carcass weight. Age probably also accounts for the significantly greater fat depth at the P8 site for carcasses from the Brahman-cross cattle. It is concluded from our results that any technique for assessment of butt shape score must consider assessment of both the lateral and dorsal aspects of the carcass in order to achieve a reasonable estimation of carcass value of cattle of different genotypes and that there may be a need to adjust this assessment for carcass fatness. ACKNOWLEDGMENTS The authors wish to acknowledge the valuable assistance Mr W. Vowles, Mr D. Roberts and Mr R. Ballandis of the Department of Agriculture, Victoria; Mr I. Loxton of the Queensland Department of Primary Industries; MS D. Perry, Mr W. McKieman and Mr A. Yeats NSW Agriculture, in collecting the data used in this paper. This work was supported by funds from the Meat Research Corporation. REFERENCES BUTLER-HOGG, B. W. and KIRTON, A. H. (1989). ` The Automated Measurement of Beef.' (Eds L. E. Brownlie, W. J. A. Hall and S. U. Fabiansson.) pp.83-91. (AMLC: Sydney). WOOD, J. D. (1989). ` The automated measurement of beef.' (Eds L. E. Brownlie, W. J. A. Hall and S. U. Fabiansson.) pp.67-73. (AMLC: Sydney).