EFFECTS OF THERMAL-PROCESSING ON DIGESTIBILITY AND PROTEIN-UTILIZATION OF RAPESEED MEAL OF MEDIUM AND LOW GLUCOSINOLATE TYPE IN DIETS FOR GROWING PIGS

The nutritive value of rapeseed meals (RSM) from Brassica campestris, 0 and 00-cultivars, with medium (25-55-mu-g/g defatted meal) and low (< 25-mu-g/g) level of glucosinolates (GL), normal solvent extracted meal or thermal treated in order to decrease protein ruminal degradability (Opex-process) or followed also by treating for GL-reduction, was investigated in three digestibility and balance trials with growing pigs. The GL-reduction treatment used removed 0.68 of the original GL, while Opex treated RSM's had 0.33 to 0.45 lower total GL-content than untreated RSM's. The various cultivars or differently processed RSM's were close to each other in their proximate composition. However, thermal treated 0-RSM had a slightly reduced lysine content compared to untreated meal. The efficient degradability of dry matter in the untreated RSM's was on average 0.532 and that of the Opex-treated 0.485. The digestibility of CP in different RSM's varied from 0.677 to 0.842 with no significant difference between 0 and 00-RSM's or to the RSM treated for GL-reduction (P > 0.05), although 00-RSM's tended to have higher OM and CP digestibilities compared with 0-RSM; pooled mean values being 0.638 vs. 0.715 for OM and 0.715 vs. 0.775 for CP. RSM treated for ruminant escape protein had the same or better digestibility than untreated RSM; pooled average values being 0.669 vs. 0.680 for OM and 0.746 vs. 0.757 for CP. This observation has practical importance since the same treatments of RSM could be employed for meals to be used in diets of both ruminants and pigs. In these experiments, the protein utilization was efficient and differences between the dietary treatments were small and insignificant. Heat treatment (Opex) did not decrease protein utilization despite a small reduction in lysine content.