Meat production of Friesian steers: the effect of intramuscular fat on palatability and the effect of growth rates on composition changes

Abstract

The relationship between intramuscular fat percentage and beef quality was investigated in 36 Friesian steers. A poor relationship between fatness and age was ensured by having six groups on rations increasing in concentrate content from 10 to 80%, and then slaughtering the animals after 300 days on these rations at an age of c. 17 months. The group means ranged from 202 to 276 kg for carcass weight, from 2.4 to 6.8 mm for fat depth at the 12th rib, and from 1.5 to 3.4% for intramuscular fat of M. longissimus. Up to 38% of the variation in shear force of M. longissimus could be accounted for by variation in intramuscular fat percentage but in the case of M. rectus femoris and of samples from M. semitendinosus, which had not cold shortened, the relationship between shear force and intramuscular fat percentage was not significant. These results suggest that intramuscular fat may influence tenderness through an effect on susceptability to cold shortening. Taste panel results indicated that with increased intramuscular fat percentage, the flavour, tenderness and overall acceptability of M. semimembranosus roasts improved, but there was little change in juiciness. There was no indication that differences in intramuscular fat percentage were associated with differences in muscle collagen concentration, collagen solubility, ultimate muscle pH, or adrenal cortex activity. Allometric coefficients relating measures of composition to carcass weight indicated that changes in composition with increases in carcass weight were more rapid than those reported for other growth studies. It is suggested that this was because the level of nutrition and carcass weight both contributed to the differences in composition.