Changes in the anatomical components of the hindquarters of Hereford and Brahman x Hereford F1 steers with fattening

Abstract

Animal Production in Australia 1998 Vol. 22 CHANGES IN THE ANATOMICAL COMPONENTS OF THE HINDQUARTERS OF HEREFORD AND BRAHMAN X HEREFORD F1 STEERS WITH FATTENING E.R. JOHNSONA, D.G. TAYLORB and L.M. KNOTT A B A Division of Farm Animal Studies, The University of Queensland, PO Box, 125, Kenmore, Qld 4069 Animal Production, Gatton College, The University of Queensland, Lawes, Qld 4343 SUMMARY The weights of the anatomical components in the hindquarters of Hereford and Brahman x Hereford F1 steer carcases, weighing from 88.4 kg to 351.8 kg were compared. Regression analyses showed that the Brahman x Hereford hindquarters had significantly less intermuscular fat relative to hindquarter fat weight and relative to hindquarter weight. In the regressions, the weights of subcutaneous fat, muscle and bone, and muscle-bone ratio did not vary significantly between genotypes. A comparison of hindquarters, from 30 kg to 90 kg at 10 kg intervals, showed that from a carcase weight of approximately 200 kg to 360 kg, the taurindicus hindquarters had a significantly lower weight of intermuscular and total fat and significantly heavier bone. From 240 kg to 360 kg carcase weight, the taurindicus hindquarters had significantly heavier muscle. There were no significant differences between subcutaneous fat weights and muscle-bone ratios. Keywords: Hereford, taurindicus, anatomical components, hindquarter INTRODUCTION Beef carcase evaluation systems which include conformation or shape score usually appraise this feature on the hindquarter (Anonymous 1987; Eldridge and Ball 1992). The domestic market which trades many Hereford and taurindicus types may pay premiums of up to $40 for a desirable shape compared with carcases of a less desirable shape. It is important, therefore, to understand the underlying cause of differing hindquarter shape. Taylor et al. (1990), Eldridge and Ball (1992) and Johnson et al. (1996) attributed hindquarter shape differences to fat, particularly subcutaneous fat, but a feature of these studies was that not all hindquarter components were fully examined. In the current study, all anatomical components of the hindquarters of two groups of steers, Hereford and Brahman x Hereford F1, were examined to determine their possible influence on hindquarter shape. MATERIALS AND METHODS Twenty-seven Hereford and 25 Brahman x Hereford F1 steers were serially slaughtered from 197 kg to 614 kg liveweight, producing carcases which ranged from 88.4 kg to 351.8 kg. When the carcases were chilled, one side from each was divided into forequarter and hindquarter at the 10th rib and both quarters were dissected into their anatomical components, muscle, bone, subcutaneous fat, intermuscular fat and connective tissue. Shape scores , assessed by an AUS-MEAT Chiller Assessor, were Herefords (10A, 4B, 11C and 2D) and Brahman x Hereford (6A, 3B, 13C and 3D). Regression analysis was used to study the growth of hindquarter subcutaneous and hindquarter intermuscular fat relative to hindquarter fat weight, and all anatomical tissues relative to hindquarter weight. RESULTS Regressions of subcutaneous (SC) and intermuscular (IM) fat of the hindquarter over hindquarter fat weight (Figure 1A) and over hindquarter weight (Figure 1B) are shown for the two genotypes. Relative to hindquarter fat weight, the Brahman x Hereford (Ti) carcases had more hindquarter subcutaneous fat than the Hereford (H) carcases at all stages, but less hindquarter intermuscular fat. When compared on the basis of hindquarter weight, the cross-bred carcases had less hindquarter subcutaneous fat and less hindquarter intermuscular fat. In all regressions, the only significant difference between genotypes was in the slopes for hindquarter intermuscular fat. Figure 2 shows the regressions of hindquarter muscle weight and hindquarter bone weight on hindquarter weight. There were no significant differences between the slopes or intercepts of either carcase component, between genotypes. 169 Animal Production in Australia 1998 Vol. 22 A B Figure 1. Relationships between subcutaneous and intermuscular fat of the hindquarter and (A) hindquarter fat weight and (B) hindquarter weight Figure 2. Relationships between hindquarter muscle weight and hindquarter weight 170 Animal Production in Australia 1998 Vol. 22 Figure 3 shows regressions of muscle-bone ratio on hindquarter weight for the two genotypes. There were no significant differences between slopes or intercepts. In Table 1, the weight differences in hindquarter components are compared between genotypes. DISCUSSION There were minimal compositional differences in the anatomical components of the hindquarters of Hereford and Brahman x Hereford steer carcases in the present study, which covered a weight range from veal to heavy export carcases. In the regressions, only intermuscular fat varied significantly between genotypes. Table 1 gave an indication of differences in hindquarter components as the cattle grew from veal to domestic carcase weight and then on to export weights. Once again the role of intermuscular fat was shown to be important. Up to about 160 kg carcase weight, there were no significant differences between hindquarter components. At about 200 to 240 kg carcase weight, the Herefords had 1.8 to 2.5 kg of extra hindquarter fat, attributable mainly to intermuscular fat, and the taurindicus hindquarters showed a significantly greater weight of muscle. At export carcase weights, the Hereford hindquarters had significantly more total fat, made up principally of intermuscular fat (2.4 to 2.8 kg) and significantly less muscle (approximately 3 to 3.7 kg). Commercially, the differences between the two genotypes are probably not very important up to 200 kg Figure 3. Relationships between hindquarter muscle-bone ratio and hindquarter weight Table 1. Weight differences in components of taurindicus hindquar ters relative to Hereford hindquarters Hindquarter weight (kg) Component SC fat IM fat Total fat Muscle Bone M/B ratio a a 30 ns ns ns ns ns ns 40 ns ns ns ns ns ns 50 ns -1.186 -1.782 ns +0.548 ns 60 ns -1.582 -2.519 +1.860 +0.730 ns 70 ns -1.978 -3.254 +2.473 +0.910 ns 80 ns -2.374 -3.990 +3.087 +1.091 ns 90 ns -2.770 -4.725 +3.700 +1.272 ns Hindquarter weight x 4 is approximate carcase weight. SC Subcutaneous; IM Intermuscular; M/B Muscle to bone; ns, not significant. All differences shown are significant (P<0.05). 171 Animal Production in Australia 1998 Vol. 22 carcase weight because the extra intermuscular fat would be sold, legitimately, as beef. Beyond 200 kg, muscle differences began to become important and any suggested superiority in shape was not supported by the excess fat and lower muscle content. However, this does not involve all cattle. Some carcases, even when corrected for fatness, do show a range in muscle-bone ratio (Kempster 1978; Purchas et al. 1991). Over all weight ranges, subcutaneous fat and the important muscling indicator, muscle-bone ratio did not vary significantly. It is likely that, up to 200 kg carcase weight, shape differences between the hindquarters of taurindicus and Hereford cattle are not commercially important, but after 200 kg, shape and yield are negatively correlated (Harrington 1972; Dumont 1978; Kempster 1978). A problem with scientific studies of shape differences in carcases is, that for over 40 years, shape has been studied mainly by reference to weights or proportions of carcase components (Butler et al. 1956; Callow 1961; Kempster 1978; Taylor et al. 1990; Johnson et al. 1996) and not by morphometric methods. On a weight basis, intermuscular fat in the current study seems likely to play a greater role in shape differences than subcutaneous fat, even though Callow (1961) and Butterfield (1966) noted that subcutaneous fat was the component best positioned to influence shape. Perhaps the shape differences between British and taurindicus types are genotypic expressions which are better explained by a morphometric approach, whereas the weight of carcase components is more of a commercial statement. REFERENCES ANON (1987). AUS-MEAT Language, Authority for Uniform Specifications Meat and Livestock (Australian Meat and Live-stock Corporation: Sydney). 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