TYPE OF FEEDING OF STRAW IN A FATTENING DIET FOR BEEF BULLS - DYNAMICS OF DIGESTION, RUMEN FERMENTATION CHARACTERISTICS, ANIMAL PERFORMANCES AND MEAT CHARACTERISTICS

The type of feeding of straw in concentrate fattening diets was studie d in two trials for both the metabolic aspects and the animal performa nces. The metabolic study was conducted with two groups of four Belgia n Blue bulls, dual purpose type, fitted with a rumen fistula and penne d in metabolism stalls for two consecutive periods of 56 days. During the first period the bulls of the first group received separately stra w and a fattening concentrate composed of dried sugar beet pulp (40.8% ), cereals (37%), oil cakes (18%), molasses (3%) and a mineral supplem ent (1.2%). The second group received the same concentrate diet mixed with chopped straw at a rate of 91 to 9% respectively. During the seco nd period the diets were changed. In the production trial the same die ts were given to two groups of six 10-month-old bulls, maintained in a free stanchion barn with straw as bedding. Both diets were given duri ng the whole fattening period, which lasted for 153 and 144 days in th e groups offered the straw separately or mixed, respectively. Apparent digestibility was systematically higher in the mixed diet group. Nylo n bag incubations in the rumen for different feedstuffs indicated high er degradability with the mixed diet for feedstuffs high in starch (P < 0.001) and with slowly degradable fibre (P < 0.05). Rumen pH was sys tematically higher in the mixed diet indicating a buffering capacity o f chopped straw. The length of the rumen papillae and the number of ke ratinized cell layers were higher with the mixed diet. In both trials feed intake was higher when concentrate and straw were given separatel y. The feed conversion ratio was lower (7.0 vs 7.4 kg/kg) while the da ily growth rate (1.5 vs 1.4 kg/day) and carcass weight (402.7 vs 371 k g) were higher with the mixed diet. Similarly, a tendency towards a hi gher dressing percentage (65.8 vs 62.6%) and muscle proportion (83.7 v s 78.3%) was also observed with the mixed diet.