OPTIMIZATION OF RAPESEED MEAL USE FOR FATTENING BULLS

Two experiments were conducted in order to optimize the incorporation of rapeseed meal
(RPM) in diets for growing and fattening of bulls. In a first experiment, the effects of 20% of a low glucosinolate (LG) RPM (3.14 mmoles/g DM of concentrate) were studied. In a second experiment, various proportions (0, 10, 20, 34%) of an LG- industrial RPM were tested in order to determine the optimal level in diet of young bulls. Thirty six young Belgian White Blue bulls were used. In the two experiments, large amount of industrial RPM (20 - 34%) did not reduce animal performance whatever the parameter considered (liveweight, daily weight gains, food intake, feed conversion, carcass weight, dressing percentages). Values did not also vary with the level of LG-RPM in the diet. Any effects were observed on the thyroid weight and the size of thyroid follicles. The secretion of thyroid hormones was not affected by RPM except for a decrease (P < 0.05) in the production of thyroxin by thyroid tissue decreased (P < 0.05) with 34% in the diet in Experiment 2. Results concerning plasma testosterone and cortisol contrasted between the two experiments with negative effects or no influence of LG-RPM. It was concluded that levels 20 ≤ A < 34% of double 00 – RPM in diet may be used for fattening bulls but investigations are still needed to outline the long-term effects on steroids and reproductive performance