Characteristics of steers of six beef breeds fattened from eight months ofage and slaughtered at a target level of intramuscular fat - I. Growth performance and carcass quality

Growth performance and carcass quality of 132 steers originating from six b eef breeds, Angus (AN), Simmental (SI), Charolais (CH), Limousin (Li), Blon de d'Aquitaine (BL), and Piedmontese (PI), fattened under the same conditio ns on the same diet, were compared at a target level of 3.5% intramuscular fat (IMF) in the M. longissimus dorsi. This target level was set on basis o f the results of a preliminary study investigating, with 784 persons, the v isual preference of marbling using photographs. The total mix ration, provi ded at ad libitum access, consisted of maize silage, grass silage and conce ntrate (52%, 26% and 22% of DM, resp.). Series 1 was performed in a tie-sta ll barn while a loose-housing system with straw bedding was used in series 2. The animals were assigned to slaughter either when the target IMF conten t was reached according to the estimation with a real-time ultrasound syste m applied in the live animals or when 15 months of fattening had passed. AN , SI, CH and LI reached 3.5% IMF on average at final weights of 501 +/- 43, 628 +/- 60, 693 +/- 117 and 668 +/- 65 kg, respectively. BL and PI did not reach this target, although the average fattening period was about three t imes longer for BL and PI than for AN and the final weights were 758 +/- 93 and 647 +/- 64 kg, respectively. Under the conditions of this experimental approach, daily gains were highest in AN, followed by CH, SI, LI and BL an d lowest in PI. The daily feed intake was significantly lower for PI than f or CH, SI and AN. The AN expressed the best feed conversion efficiency in t erms of DM expenditure per kg gain over the complete fattening period while this efficiency was lowest in the PI group followed by BL. Among the four breeds, which reached the target IMF content, LI steers showed the greatest proportion of premium cuts and the highest lean to fat and lean to bone ra tio in the sirloin, followed, in descending order, by CH, SI and AN. Howeve r all four groups were graded around 4 in fatness score (high to very high) . The present results revealed for all breeds the difficulty to reach the d esired extent of marbling and at the same time favourable carcass conformat ion, carcass size (except AN) and fat cover which meet market demands.