Abstract:
Animal Production in Australia 1998 Vol. 22 THE RELATIONSHIP OF CHEMICALLY DETERMINED FAT IN THE TENTH RIB EYE MUSCLE TO VISUAL MARBLING SCORE AND FAT THICKNESS E.R. JOHNSON and L.M. KNOTT Division of Farm Animal Studies, The University of Queensland, Qld 4072 Chiller assessment of beef carcases in Australia includes a subjectively determined marbling score. This paper examines the accuracy and reliability of visual marbling score relative to chemically determined marbling fat and fat thickness measurements. Rump P8 fat thickness (P8) and 12th rib fat thickness (FT12) were measured in 132 Santa Gertrudis steer carcases. A one-centimeter thickness of M. longissimus at the 10th rib was trimmed of external fat and its intramuscular fat was determined by ether extraction. The AUS-MEAT Chiller Assessor s marbling scores were noted. Correlation and regression analyses were used to study the relationship between chemical fat on one hand, and P8, FT12 and visual marbling score on the other. Figure 1 and the two equations show these relationships. 10.00 Marbling fat (%) 8.00 6.00 4.00 2.00 0.00 0 y = 1.86x + 0.85 R2 = 0.43 1 2 Vis ual marbling score 3 4 Figure 1. Relationship of chemical fat to visual marbling score Chemical fat (%) = 0.0565 P8 + 2.472 Chemical fat (%) = 0.0459 FT12 + 2.480 R2 = 0.04 R = 0.05 2 s.e. = 1.61% s.e. = 1.60% Visual marbling score, P8 and FT12 were poorly related to chemically determined marbling fat. A marbling score of 1 was associated with a variation of about 1% to 6% chemical fat; a marbling score of 2 showed a variation of about 2.5% to 8.5%; a marbling score of 3 (six carcases only) showed a variation of about 3.7% to 8.0% chemical fat. Lot feeders preparing cattle for the Japanese market feed cattle for up to 240 days, primarily to increase marbling fat. However, a study of 15,000 carcases by Browne and Beasley (1991) found that visual marbling score in grass-fed carcases was 2.3, and in grain-fed carcases, 2.4. This suggested that attempts to increase marbling by lengthy lot-feeding were not succeeding, and that visual marbling scores were concentrated at the lower end of the marbling scale. This study shows that chemical fat in tenth rib eye muscle is poorly related to subcutaneous fat thickness and marbling score. Visual marbling score does not appear to be sufficiently accurate to evaluate the progeny of beef sires, which Baud et al. (1994) found to vary considerably in their ability to marble. BAUD, S., GODDARD, M. and HYGATE, L. (1994). Project M112, Meat Research Corporation, Sydney. BROWNE, G.M. and BEASLEY, R.C. (1991). Research Project No. 28, Livestock and Meat Authority of Queensland. 295
