THE EFFECT OF HEAT TREATMENT AND ENZYME HYDROLYSIS OF RAPESEED MEAL ON THE PERFORMANCE OF BROILER CHICKENS

An experiment was conducted on the effect of heat treatment and conditions of enzyme hydrolysis of Tower and Midas rapeseed (Brassica napus) meal (RSM) on the concentration of nitriles and goitrin in the meals and their biological effect when fed to broiler chickens. Autolysis of raw meals resulted in a high level of nitriles in Midas RSM and a low level of nitriles in Tower RSM. In heated meals, goitrin was the principal hydrolysis product being high in Midas and low in Tower RSM. An increase in incubation time and freeze-drying after hydrolysis reduced the total nitriles. Non-hydroxy epithionitriles were most susceptible to treatments imposed and a hydroxy nitrile, 1-cyano-2-hydroxy-3-butene, was least affected by freeze-drying. Feeding 20% raw or heated Tower RSM hydrolyzed in different ways had little effect, compared to the soybean control, on rate of growth, feed efficiency, mortality or incidence of perosis. Thyroid gland weights in the treated groups were two to three times greater than the controls. Feeding 20% raw or heated Midas meal decreased rate of growth and increased feed required per unit of gain. The growth depression was greater with raw Midas RSM than with the heated meal. Thyroid gland weights in the groups fed Midas RSM, either raw or heated, were larger than for Tower RSM. Thyroid gland weights were 4–20 times as large as the controls. Raw or heated Midas RSM prepared by pre-hydrolysis and freeze-drying (PHFD) caused a greater decrease in rate of gain than other Midas meals in which 2% raw or heated ground Midas rapeseed was included in the rations fed.