Changes in intermuscular fat colour in steers fed a feedlot ration for varying lengths of time. (Short Communication)

Abstract

CHANGES IN INTERMUSCULAR FAT COLOUR IN STEERS FED A FEEDLOT RATION FOR VARYING LENGTHS OF TIME M. JEFFERY*, T. JAMES*, I. LOXTON** and R. SHEPHERD** Fat colour is becoming increasingly important in determining the suitability of carcases for premium export beef markets, especially those in Japan and Korea. A recent survey, (Browne and Beasley 1991) found that up to 4% of steers from southern and Central Queensland targeted at the grass fed Japanese beef market had an unsuitable intermuscular fat colour, with AUSMEAT scores above 7. Carcases with yellow fat (scores > 7) are often graded into lower priced markets, reducing returns to beef producers and limiting marketing options for meat processors. Feeding high grain rations to Bos taurus steers in feedlots for up to 112 days has been shown to improve (whiten) intermuscular fat colour in beef carcases (Forrest 1981). There is little information available on the time and extent of major fat colour changes in the carcases from Bos indicus steers fed feedlot diets. This experiment investigated the time and extent of major fat colour changes in previously grass fed steers once they were placed in a feedlot. Ninety six Bos indicus cross steers approximately three years old, which had been grazing b@el/rhodes grass pastures for the previous 12 months, were allocated for turnoff after 0, 42, 56, 91 and 119 days in the feedlot. All steers had a 21 day introductory feeding period before being placed on an Ad lib ration (76% grain, 10% roughage, 14 % concentrates) for their remaining period in the feedlot. Mean intakes for the periods day 0 to 42, day 42 to 56, day 56 to 91 and day 91 to 119 were 10.1, 13.0, 13.0 and 13.5 k&d/day respectively. At slaughter, carcase weight, subcutaneous fat depth at the (P8) rump site and the visual assessment of intermuscular fat colour using the AUSMEAT chiller assessment system were recorded. Table 1 Carcase attributes of steers fed in a feedlot for different time periods 7B Mean AUSMEAT intermuscular fat colour scores decreased (fat colour whitened) at each turnoff between day 0 and day 91 (Table 1). At day 0, 61% of animals had fat scores greater than 5, with a range from 2 to 7. By day 42, all steers had fat scores of 5 or less, with 73% of carcases having intermuscular fat colours less than score 5. This percentage had increased to 89% by day 56 and to 94% by day 91. There was no improvement in intermuscular fat colour between day 91 and day 119. Strachan, Yang and Dillon (1993) found significant decreases in AUSMEAT fat colour scores between day 0 (mean score 3.9) and 35 (mean score 2.4), but no further significant decreases in mean fat colour from day 35 to 175 (mean score 1.7). The difference in results between these two studies may have been due to the much higher initial fat colours in the present experiment. The results from this experiment, with most carcases having scores ~4 by day 56, show that short term feedlotting can be useful in reducing fat colour, therefore increasing the number of grass-fed steers suitable for premium export markets. The financial support of the Meat Research Corporation and the assistance of Queensland Department of Primary Industries staff is gratefully acknowledged. Browne, G.M. and Beasley, R.C. (1991). Livestock and Meat Authority of Queensland. Research Rpt. No.28. Forrest, R.J. (1981). Can. J.Anim.Sci. 61: 575. Strachan, D.B., Yang, A and Dillon, R.D. (1993). Aust. J. Exp. Ag 33 (3) In press. *Queensland Department of Primary Industries, Brigalow Research Station, M.S. 58'6, Theodore Q 4719. **Queensland Department of Primary Industries, PO Box 6014, Rockhampton Q 4700.