Abstract:
Proc. Aust. Soc. Anim. Prod. 1994 Vol. 20 IMPROVING BEEF MARKETING EFFICIENCY BY USE OF THE ANAL FOLD CALIPER G.M. BROWNEA and E.R. JOHNSON B ALivestock and Meat Authority o f Queensland, PO Box 440, Spring Hill, Qld. 4004 *Dept of Farm Animal Medicine and Production, The U nivcrsity of Queensland, Qld. 4072 SUMMARY A less expensive and easier to use prototype anal fold caliper than the previous version was developed and tested. The prototype' design was based on the Harpenden Skinfold Caliper, used to predict human s body density and subsequently modified for use with live cattle. The ability of anal fold fat thickness (AFFT), measured by the prototype caliper, to predict carcase composition in the live animal was compared with that of hot standard carcase weight (HSCW) and P8 fat depth in the carcase. Rib sets from 48 steers, 24 lightweight (c 252 kg HSCW) and 24 heavyweight (> 252 kg HSCW) were dissected into muscle, subcutaneous fat, intramuscular fat, bone and connective tissue. Carcase fat percentage was predicted by AFFT with an R' = 0.49 and a standard error of the estimate (SEE) = 3.60. It was superior to P8 alone (R' = 0.36, SEE = 4.05) and only marginally inferior to P8 and HSCW (R' = 0.51, SEE = 3.58). Carcase muscle percentage was predicted less accurately (R'= 0.35, SEE = 2.79). Anal fold fat thickness was marginally superior to P8 (RZ = 0.33, SEE = 2.83) but not as accurate as P8 with HSCW (R' = 0.42, SEE = 2.66). Keywords : anal fold caliper, anal fold fat thickness, carcase composition. INTRODUCTION Over recent years the Australian beef industry has begun to focus on product quality. This emphasis stems largely from the importance of premium export markets, such as Japan, coupled with the desire to arrest the decline in domestic beef consumption. The greater emphasis on quality accompanies a need to trade on tight product specifications. Consequently the marketing of slaughter cattle has become a more complex task. An important specification is subcutaneous fat depth. Browne (1992) reported that 7% of carcases destined for the Japanese grassfed market were downgraded for either inadequate or excessive fat coverage. Costs extend beyond the downgrading of carcases and loss of premiums. Further costs are incurred through the labour required to trim excessive fat, and loss of meat yield. Charles (1977) demonstrated that for every millimetre increase in 12th rib fat thickness between the range of 1 and 15 mm, beef yield decreased by approximately 1%. If beef producers are better able to determine when their cattle have the appropriate level of subcutaneous fat for the target market, substantial benefits would accrue to both the production and. processing sectors of the beef industry. Fatness in live cattle can be assessed visually or by using ultrasound devices. However, Charles (1974) demonstrated that a measurement of the anal fold, which consists of the skin (2 layers) and enclosed subcutaneous fat between the point of the ischium and base of the tail, could also be used to reliably predict carcase muscle and fat percentages. Johnson and Davis (1983) modified the Harpenden Skinfold Caliper (used originally to predict human body density) to measure anal fold fat thickness (AFFT) in live cattle, and were able to predict carcase muscle and fat percentages with an accuracy comparable to that of 12th rib fat thickness measured on the actual carcase. In this paper we report the results of using a new anal fold caliper which retains all the engineering specifications of the modified Harpenden Skinfold Caliper, but. is constructed of alloy and has only one moving part in order to reduce its cost. The ability of AFFT, measured by this caliper, to predict carcase composition was compared with predictions of composition from carcase P8 fat thickness and P8 plus hot standard carcase weight (HSCW). Development of prototype caliper MATERIALS AND METHODS The prototype caliper was manufactured by an engineering firm, Roblan Pty Ltd, to the same engineering specifications, but of different materials and form, to the modified Harpenden Skinfold Caliper described by Johnson and Davis (1983). Prediction of carcase muscle and fat percentage using the prototype caZiper The AFFT of 2 groups of steers ('lightweight' and 'heavyweight') was determined according to the technique outlined by Charles (1974). The measurements were made at the abattoir immediately prior to 116 Proc. Aust. Sot. Anim. Prod. 1994 Vol. 20 slaughter. Cattle were restrained in a race or a mechanical restrainer to allow reliable measurement. After slaughter HSCW and P8 fat depth were measured by abattoir personnel. Details of the carcases are shown in Table 1. Table 1. Means 2 standard deviations (s.d.) and ranges for anal fold fat thickness (AFFT, mm), hot standard carcase weight (HSCW, kg), P8 (mm), estimated carcase fat percentage (CF%) and estimated carcase muscle percentage (CM%) of the carcases studied The carcases of all steers were identified in the boning room after overnight chilling and a rib set (6 rib) was collected from each. Using a part-carcase dissection method described by Johnson and Charles (1981) the rib sets were dissected into their component tissues of muscle, subcutaneous fat, intermuscular fat, bone and connective tissue. The percentages of muscle and fat in the rib sets were used to indicate the proportions of each tissue within the carcase. Using the dissection data, simple regression analyses were conducted to assess the caliper' ability to s predict carcase muscle and fat percentages. Data were grouped into HSCW ranges broadly describing 'domestic' (170-250 kg) and 'export' (253-314 kg) carcases in order to generate prediction equations. RESULTS Carcase fat percentage (estimated from rib set dissections) was predicted more accurately by AFFT in the lightweight steer sample (R' = 0.58, standard error of estimate (SEE) = 3.27) than in the heavyweight (R' = 0.42, SEE = 3.68) or combined steer samples (R' = 0.49, SEE = 3.60). The addition of HSCW to AFFT in the lightweight carcases did not improve the prediction (Table 2). Carcase muscle percentage (estimated) was predicted more accurately by AFFT than P8 in both the lightweight (R' = 0.46, SEE = 2.71) and combined (R' = 0.35, SEE = 2.79) groups (Table 3). Anal fold fat thickness was more accurate than P8 plus HSCW in the lightweight steers (R' = 0.41, SEE = 2.89). Fat depth at P8 predicted muscle percentage in the heavyweight carcases more accurately than AFFT. The addition of HSCW to either AFFT or P8 did not significantly improve the amount of variation which was explained in any of the groups. DISCUSSION This project demonstrated that the prototype anal fold caliper provides a relatively accurate estimation of carcase composition in cattle prior to slaughter. Overall, AFFT predicted carcase fat and muscle percentages with better than, or comparable accuracy to, P8 or a combination of P8 and HSCW in the carcase. However, AFFT predicted fat percentage more accurately than muscle percentage, and provided a better prediction of both fat and muscle percentages in the lightweight steers than in the heavyweight steers. These findings were probably attributable to the greater degree of fatness in the lightweight steers 117 Proc. Amt. Sot. An' Prod. 1994 Vol. 20 irn. Table 2. Regression of estimated carcase fat percentage (CF%) over anal fold fat thickness (AFFT), PS and hot standard carcase weight (HSCW) in lightweight steers (< 252 kg HSCW), heavyweight steers (> 252 kg HSCW) and the combined group Table 3. Regression of estimated carcase muscle percentage (CM%) over anal fold fat thickness (AFFT), P8 and hot standard carcase weight (HSCW) in lightweight steers (< 252 kg HSCW), heavyweight steers (> 252 kg HSCW) and the combined group 118 Proc. Amt. Sot. Anim. Prod. 1994 Vol. 20 and the fact that both muscle and fat content were being estimated primarily from a fat thickness measurement. It should be noted that in this study, P8, the carcase fat thickness measurement used, was a relatively poor predictor of carcase composition compared to carcase fat thickness measurements in similar studies (Johnson and Davis 1983). This may have resulted from the fact that the P8 measurements were taken by abattoir staff. The addition of HSCW to AFFT generally increased the amount of variation which was explained by the prediction of both fat and muscle percentages, albeit not significantly. It is recommended that HSCW, which is always available and is usually a major contributor to the determination of carcase composition, should be routinely used in composition studies. Whilst in the practical situation an animal' liveweight would be used in conjunction with AFFT, rather than HSCW, these data were not s available in this study. Beef cattle producers, who sell on a weight-at-works basis, could use the prototype caliper to complement their marketing strategies by assisting them to select appropriate cattle for sale. Used in conjunction with a 'ready reckoner' which equates AFFT to fat percentage and P8 fat depth, and the producers' knowledge of market specifications, the caliper has the ability to increase net returns from cattle sold. Ultrasound devices are available which can measure carcase fatness with a high degree of accuracy (Porter et al. 1990; Robinson et al. 1992). However, they are more expensive and complex in their interpretation than the prototype caliper and may not be feasible for many producers. It is envisaged that the caliper will retail for approximately $400. It is concluded that the prototype anal fold caliper would be a useful field guide to estimate carcase fatness in live cattle and hence their market suitability. ACKNOWLEDGMENTS This project was funded by the Meat Research Corporation and the Livestock and Meat Authority of Queensland. Our thanks are also extended to the co-operating processors, and Messrs David Robertson and Eric Martin (Roblan Pty Ltd) for their technical assistance. REFERENCES BROWNE, G.M. (1992). Proc. Amt. Sot. Anim. Prod. 19: 91-3. CHARLES, D.D. (1974). Res. Vet. Sci. 16: 89-94. CHARLES, D.D. (1977). Amt. J. Agric. Res. 28: 1133-9. JOHNSON, E.R. (1987). Amt. J. Exp. Agric. 27: 613-7. JOHNSON, E.R. and CHARLES, D.D. (1981). Aust. J. Agric. Res. 32: 987-97. JOHNSON, E.R. and DAVIS, C.B. (1983). Amt. J. Agric. Res. 34: 82532. PORTER, S.J., OWEN, M.G., PAGE, S.J. and FISHER, A.V. (1990). Anim. Prod. 51: 489-95. ROBINSON, D-L., MCDONALD, CA., HAMMOND, K. and TURNER, J.W. (1992). J. Anim. Sci. 70: 1667-76. 119