EFFECT OF FEED PROTEIN ON CARCASS COMPOSITION AND MEAT QUALITY IN STEERS

Forty-five Charolais steers were fed one of four experimental regimes containing maize silage and maize grain supplemented with either protected soyabean-rapeseed meal or linseed meal. The first three regimes were formulated to supply the same energy and different protein levels with soya-bean-rapeseed meal: low (L-SRM), medium (M-SRM) and high (H-SRM). The fourth regime consisted in feeding the same amount (kg/day) of linseed meal as that of soyabean-rapeseed meal in the H-SRM regime (LSM). As the protein level increased from L-SRM to H-SRM, the daily weight gain of steers increased and the carcass composition was changed towards higher muscle and lower fat proportions. Though the actual supply of feed protein by regime LSM was close to that achieved with M-SRM, the effect of linseed meal supplementation on weight gain and carcass composition was comparable to that obtained by feeding the high protein level (H-SRM). The dry matter content increased and the heme pigments and lipids contents decreased in longissimus thoracis muscle as the protein supply increased from the low to the high level. Again the amplitude of the differences in meat quality with L-SRM were similar in H-SRM and LSM. Muscle colour, connective tissue and mechanical strength remained practically unaffected by the protein treatments. However, meat was scored less tender in H-SRM and less juicy in treatment LSM than in treatment L-SRM. The results obtained with linseed meal suggest a specific effect of type of feed protein on beef carcass composition and meat quality.