Influence of feeding intensity, grazing and finishing feeding on muscle fibre characteristics and meat colour of semitendinosus, longissimus dorsi and supraspinatus muscles of young bulls.

Forty-one autumn-born Friesian bull calves were allocated to two production systems (Extensive='E' and Intensive='I'). In the E-system, animals were loose-housed and fed a roughage-based diet from October to May, followed by a grazing period from May to October. Ten animals were slaughtered directly from pasture (360 kg BW) and 11 after a 10-week finishing feeding in tie-stalls (460 kg). E-bulls were compared with intensively fed tie-stall housed young bulls (I) slaughtered at comparable weights (360 kg, n=11 and 460 kg, n=9). Semitendinosus (ST), longissimus dorsi (LD), and supraspinatus (SU) muscles were analysed histochemically, and the meat analysed for colour and pigmentation. In LD and SU, Type I % was higher in E- compared with I-bulls (P<0.05-0.006). In ST and LD, Type IIA % was higher in E- compared with I-bulls (P<0.01-0.009). As a result, Type IIB % was lower in all three muscles in E- compared with I-bulls (P<0.05-0.001). In E- compared with I-bulls, Type IIA and IIB fibre areas were larger in ST (P<0.05-0.03) and capillarization was higher in both ST and LD (P<0.001). In all three muscles, the activity of citrate synthase was higher (P<0.07-0.001) and that of lactate dehydrogenase lower (P<0.003-0.001) in E- compared with I-bulls. E-bulls had lower glycogen content than I-bulls in ST and LD at 360 kg, but higher at 460 kg following finishing feeding (P<0.008-0.001). Meat colour (lightness) was darker (P<0.001) and pigmentation was higher (P<0.001) in ST and LD of E- compared with I-bulls, with no effects in SU. In conclusion, histochemically different muscles respond differently to changes in the production system, and differences between the extensive and the intensive production system were narrowed after the finishing feeding.