Further studies on the sources of thiocyanate ion in the excreta of poultry fed low‐glucosinolate rapeseed (Brassica napus) meal

Balance trials utilising intact (control) and caecectomised laying hens to emphasise hindgut fermentation were conducted to further investigate the sources of thiocyanate ion (SCN) in the excreta of poultry fed lowglucosinolate rapeseed (Brassica napus L) meal (LG RSM). Meals varying in amounts of indole glucosinolate degradation products were prepared from defatted low‐glucosinolate rapeseed by subjecting this meal to varying degrees of heat treatment and by solvent extraction. Final quantification of degradation products was conducted on commercial LG RSM. Lack of correspondence between indole glucosinolates decomposed and SCN released in hindgut fermentation indicated the presence of an unidentified thermal degradation product(s) of indole glucosinolates in defatted low‐glucosinolate rapeseed subjected to prolonged (60 min) heat treatment and in commercial LG RSM. The concentration of the degradation product(s) was estimated to be 1.4‐1.9 μmol g −1 in two samples of LG RSM. Fractionation experiments showed the compound(s) to be relatively insoluble in ethanol when compared with intact indole glucosinolates. Hindgut fermentation of hydroxybenzyl‐glucosinolate resulted in a low production of SCN, and laying hens were shown to excrete free SCN readily.