ADIPOSE-TISSUE PARTITIONING OF LIMIT-FED BEEF-CATTLE AND BEEF-CATTLE WITH AD-LIBITUM ACCESS TO FEED DIFFERING IN ADAPTATION TO HEAT

We compared fat distribution and lipoprotein lipase (LPL) activity in steers differing in adaptability to the subtropics. Steers were fed a grain diet (3.13 Mcal ME/kg DM) at limited (150 kcal ME.kg(-.75).d(-1) ;.23 kg ADG) or ad libitum levels for 140 d, then slaughtered. Sixteen British- (8 Angus, 8 Hereford; S), 16 Boran- (R), 16 Brahman- (B), an d 16 Tuli- (T) cross steers from MARC III composite cows were used. Ad ipose tissue samples from perirenal, omental, and subcutaneous depots were analyzed for LPL activity. Carcass measurements including omental , external, and seam fat trim from 1/2 of the carcass were measured. S ubcutaneous fat had greater (P < .05) LPL activity than fat from the o ther depots. Generally, there were no differences (P > .05) in fat dis tribution for steers fed at limited levels. Means for ADG, slaughter w eights, carcass weights, yield grades, and carcass lipid weights for S and B fed for ad libitum intake were greater (P < .05) than those for T and R. Marbling was greatest (P < .05) for S and did not differ (P > .05) for the other breeds with ad libitum intake. Factor analysis of fat depots for animals with ad libitum intake indicated that Bos taur us cattle differing in adaptation to heat deposited fat differently; S deposited greater (P < .05) proportions of carcass fat and T deposite d greater (P < .05) proportions of internal fat. It seems that accumul ation of internal fat is detrimental for ADC for Bos taurus cattle.