INCORPORATION OF RAPESEED MEAL EXTRACTED BY PRESSURE IN A DIET FOR GROWING FATTENING BULLS .1. INTAKE, DIGESTIBILITY AND FERMENTATION IN THE RUMEN

Intake, digestibility, degradation kinetic and fermentation were studi ed with bulls offered fattening diets with four different incorporatio n rates of rapeseed meal obtained by pressure; the ether extract conte nt was 8.6% and the glucosinolate content 17,6 mu molg. The control di et was made of sugar beet pulp, cereals, soya bean meal and linseed me al. In the three other diets, nitrogen from rapeseed meal provided 33, 66 or 100% of nitrogen from soya bean meal or linseed meal. The intak es of the control diet were 94.3 +/- 7.3 g/kg metabolic body weight. I ntakes were maintained high in the diet with 33, 66 or 100% of protein from rapeseed meal at 93.5 +/- 7.7; 93.0 +/- 5.0 and 93.5 +/- 7.7 g/k g, respectively. The apparent digestibility of rapeseed meal in the ra tion containing only rapeseed meal was high at 74.9 +/- 1.9% for dry m atter, 76.5 +/- 2.1% for organic matter, 69.9 +/- 3.9% for nitrogen, 5 9.1 +/- 4.8% for ADF and 74.6 +/- 6.9% for ether extract. Dry matter o f rapeseed meal was less degradable (57.8 +/- 5.0%) than that of soya bean meal (65.5 +/- 2.6%) or of linseed meal (61.6 +/- 4.2%) but was n ot as well protected than that of protected soya bean meal (43.6 +/- 2 .6%) (P < 0.001). Similar trends were observed for the degradability o f nitrogen (P < 0.001). Ether extract of rapeseed meal was more degrad able than that of linseed meal (P < 0.001). There were no significant effects of the incorporation rate of rapeseed meal on the pH in the ru men. The fermentations were mainly of the acetate type with usual conc entrations of propionate, butyrate, total volatile fatty acids, glucos e or alpha amino nitrogen. Ammonia concentration was higher with the c ontrol diet and lower with the diet with 100% of protein from rapeseed meal. Fatty acids of rapeseed meal were more protected against satura tion by the rumen microorganisms than in linseed meal.