OPTIMAL LEVEL OF RAPESEED MEAL IN DIETS OF LAMBS.

Two experiments were carried out in order to improve the strategy of rapeseed meal (RPM)
incorporation in the diets of lambs. In a first experiment, the effects of RPM obtained from either a high-glucosinolate (HG) cultivar (Honk RPM) or a double-low strain (Samourai RPM) were studied.
Two types of concentrates containing 25% of RPM were compared to a Control concentrate. In a
second experiment, the effects of various proportions (0 – 40%) of an industrial low glucosinolate (LG)-RPM were studied in order to determine the disorder-threshold in diets for young ruminants. One hundred forty six Texel, Suffolk or crossbred lambs ranged in age from 1 to 2 months were used.
Neither the Samourai nor the Honk RPM did affect negatively animal performance whatever the
parameter considered (growth, food intake and conversion, slaughter performances). Low (P < 0.05) proportions of C10:0, C12:0 and C14:0 and high contents of C18:1trans, C22:2 were determined in the perirenal fat of lambs receiving the Honk RPM. The industrial LG-RPM had no negative effects on animalperformance, best results were obtained with 25 and 30% of RPM. The Samourai RPM had no effect on the thyroid weight, whereas, the Honk RPM modified (P < 0.05) the histology of this organ; the percentages of large thyroid follicles being higher (P < 0.05) in the Honk group than in the Control and Samourai groups. High levels of Canola industrial LG-RPM(from 20%) induced also an hyperthyroidism. The Samourai and Honk RPM decreased (P < 0.05) the secretions of thyroid hormones while the industrial LG-RPM did not affect these hormones in any way. RPM had no significative effects on other hormones. It was concluded that disturbance in thyroid histology and activity induced by the ingestion of RPM did not affect the physiology and performance of lambs and that the levels between 25 to 30% of a LG-RPM were optimal for growing and fattening lambs.