Thirty-eight Charolais steers castrated at 2 or 10 months of age were used to study the effect of age at castration on animal performance, muscle characteristics and meat quality traits in two consecutive trials. Steers, were reared at pasture during the summer and at barn with high quality hay during the winter. The slaughter occurred at 26 months of age and 402 kg of carcass weight. ne quality of meat from M. rectus abdominis (RA) and M. triceps brachii (TB) after 14 days of ageing was evaluated by sensory analysis using three descriptors: tenderness, juiciness and flavour. The physicochemical characteristics, such as collagen amount and solubility, intramuscular fat content, p-calpain and 27 K proteasome sub-unit contents, myosin heavy chain isoform (1, Ila and fix) proportions, metabolic enzyme activities (isocitrate and lactate dehydrogenase, cytochrome-c oxydase), fibre area and type (SO, FOG and FG), were also measured. No significant differences in live weights and average daily gains appeared according to castration age. Between birth and weaning, steers castrated at 10 months had a higher weight gain (1056 vs 10 12 g/d), whereas this tendency was reversed after castration. The weight gain of 10-month castrated steers decreased between 10 and 14 months (668 vs 746 g/d) and between 14 and 20 months (918 vs 974 g/d) than the weight gain of 2-month castrated steers. FOG fibres of 10-month castrated steers had a larger area in M. rectus abdominis (3801 vs 2983 mu m 2), whereas the other fibres areas were not affected by castration age. The proportions of FOG fibres in 10-month castrated steers were higher (8.5 vs 8.1 and 22.2 vs 16.7% respectively for RA and TB muscles) whereas the FG fibres proportions were lower (52.2 vs 55.8 and 50.1 vs 54.9% respectively for RA and TB muscles). Castration age had no impact on myosin heavy chain proportions. The oxidative and glycolytic metabolisms were also not affected by castration age. The intramuscular fat content was not modified by castration age. Delaying castration age led to an increase in collagen content (p=0.04) with no impact on collagen solubility (p=0.73). The mu-calpain and the 27 K proteasome sub-unit contents were significantly lower for 10-month castrated steers than for 2-month castrated ones (75 vs 96% and 76 vs 95% respectively). Meat quality traits of tenderness, juiciness and flavour were equivalent for the two groups of steers in the two muscles. (c) 2008 Elsevier B.V. All rights reserved.