Effect of grain feeding on fat colour and other carcass characteristics in previously grass-fed Bos indicus steers

One hundred Brahman cross steers were removed from pasture and fed a high grain diet for a finishing period of 0, 35, 70, 105, or 175 days. The steers were then slaughtered and assessed for subcutaneous fat depth, fat colour, meat colour, marbling, and p-carotene and lutein concentrations in the fat and serum.The average liveweight gain was 0.7 kg/day. After35 days of grain feeding, fat colour was significantly(P<0.05) decreased from 3.9 to 2.4 when assessed using grading chips ranging from 0 (polar white) to 9 (creamy yellow). There was a trend to a further decline in fat colour over longer finishing periods (1.7 at 105 days and 2.0 at 175 days), although 1 steer had a fat colour core of 6 at 70 days and 1 at 105 days slaughter, and another had a score of 4 at 175 days. Steers fed for175 days had higher marbling but darker meat than those fed for the other finishing periods (P<0.05).Subcutaneous fat depth at 105 and 175 days (17.3 mm) was greater than at 35 and 70 days (14.5 mm) and significantly (P<0.05) greater than at the initial slaughter (12.5 mm).Fat colour was correlated (in the subcutaneous and intermuscular fat, respectively) with p-carotene (r = 0.61 and 0.55) and lutein (r = 0.53 and 0.52) concentrations, and in the serum, with p-carotene (r = 0.49) concentration. Objective assessment of fat colour, the Minolta b* value, was also correlated (in the subcutaneous and intermuscular fat, respectively) with p-carotene (r = 0.85 and 0.80) and lutein (r = 0.74 and 0.73) concentrations and was correlated with p-carotene (r = 0.61) concentrations in the serum. It was s demonstrated that grain feeding had an effect on changing bovine fat colour, and although p-carotene was predominant in serum, both p-carotene and lutein contributed to the yellowness in bovine carcass fat.