An experiment was conducted to determine if growth rate, as affected by level of feeding, during a 10-or 20-week period prior to slaughter could influence the tenderness and palatability of beef from young (approx. 14 months old at the start of experiment) steers. Steers, comprising 18 Aberdeen Angus (AA), 18 Charolais (CH) and 18 Holstein (HO) purebreds, were allocated, within genotype, to one of three levels of feeding: (a) moderate ((M/M) 750 kJ metabolizable energy (ME) per day per kg M0·75), (b) high ((H/H) 1050 kJ ME per day per kg M0·75) both for 20 weeks; or (c) moderate for the first 10 weeks followed by high for the remaining 10 weeks (M/H). The steers were slaughtered at a fixed age (approx. 19 months old) and samples ofm. longissimus lumborum(from all three genotypes) m. vastus lateralis and m. biceps femoris (from AA and CH only) separated, vacuum packed and stored at 2ºC for both 7 and 14 days before freezing. These cuts were subsequently assessed by a 12 member taste panel and texture analysis performed using Volodkevitch-type jaws.Growth rates during the final 10 weeks of the experimental period differed between dietary regimen (M/M = 0·87; M/H = 1·25; and H/H = 1·02 kg/day; s.e.d. = 0·08;P< 0·001). Steers offered the M/M level of feeding grew more slowly (0·97 kg/day) than those offered the M/H and H/H level of feeding (1·20 kg/day; s.e.d. = 0·06;P< 0·001) over the entire 20 week experimental period. In spite of these differences in growth rate, there were no consistent effects on beef tenderness and general palatability. Mean growth rates for CH, HO and AA steers were 1·21, 1·13 and 1·03 kg/day (s.e.d. = 0·06;P< 0·05). Beef samples from AA steers consistently scored better for various sensory attributes than those from CH and HO steers; this may have been due, in part, to level of carcass fatness and rate of carcass cooling post mortem. Accounting for factors such as genotype within the experimental design and slaughtering animals at a relatively constant age reduced the variance associated with each sensory attribute to 0·6 of that observed in commercial practice. The data suggest that there is little opportunity to improve beef eating quality by increasing growth rate by dietary means in steers provided that moderate levels of gain (equivalent to the UK average) are maintained.

Eighteen purebred steers of three genotypes, Aberdeen Angus (AA), Charolais (CH) and Holstein (HO), were divided within genotype into three groups of six animals and offered one of three different levels of feeding either moderate (M/M) or high (H/H) both for 20 weeks or moderate for the first 10 weeks followed by high for the remaining 10 weeks (M/H). Growth rates during the final 10 weeks of the experimental period differed between dietary regimen (M/M = 0·87; M/H = 1·25; and H/H = 1·02 kg/day; s.e.d. = 0·08;P< 0·001). Over the entire 20 week experimental period animals offered the M/M level of feeding grew more slowly (0·97 kg/day) than those offered the M/H and H/H level of feeding (1·20 kg/day; s.e.d. = 0·06;P< 0·001). Mean growth rates for CH, HO and AA steers were 1·21, 1·13 and 1·03 kg/day (s.e.d. = 0·06;P< 0·05). The animals were all slaughtered at a fixed age of 18 months, according to the Meat and Livestock Commission Blueprint for beef and, 48 h post mortem, samples of m. longissimus lumborum (LL) and m. vastus lateralis (VL) were removed for analyses.Muscle fibres were classified histochemically, according to their contractile and metabolic properties, and muscle fibre size was measured. Fibre type frequency was calculated and, in LL, the total fibre number of the muscle was estimated. There was little impact of feeding level, or consequentially growth rate, on muscle fibre frequency and size. The effects seen were confined mainly to LL where there were significant differences between the M/M and H/ H groups with respect to fast twitch glycolytic fibres (mean % frequency (M/M = 40·1 and H/H = 44·3; s.e.d. = 1·4;P< 0·01); mean % area (M/M = 51·9 and H/H 56·0; s.e.d. = 1·5;P< 0·05)) and apparent total fibre number (M/ M = 35·0; and H/H = 41·9 ✕ 104; s.e.d. = 1·7;P< 0·05) which were greater in H/H than in M/M groups. However, in both LL and VL the predominant differences were related to genotype; in particular, overall fibre size was smallest in CH, while slow oxidative (SO; type I) fibre area was highest in AA. For LL, analysis across all animals showed a positive relationship between SO area, % area, % frequency and overall acceptability of meat at 14 days as evaluated by a trained sensory panel. No such relationship was observed for VL. The data suggest that in this study manipulation of feeding level has only a small impact on muscle fibre characteristics and that the differences between genotype and muscle type may be more important in determining the variability of overall acceptability than growth rate.