Abstract
In each of two experiments cattle were given diets based on (300 g kg −1) either high (60.7 mmol g −1) or low (29.0 mmol g −1) glucosinolate rapeseed meals (HgsRSM and LgsRSM, respectively), each untreated (UT), heat-treated (HT) or with formaldehyde added (FT), with untreated soyabean meal (UTSBM) used as a control in the second experiment. Concentrations of toxic moieties, released from hydrolysis of the glucosinolates present, in ruminal and in duodenal digesta (using heifers fitted with both rumen and duodenal cannulae), and in milk and in urine, and their effect on the liver as evidenced by concentrations of glutamate dehydrogenase (GLDH) in serum and glutathione (GSH) in blood, were determined. There were no significant protein source-processing treatment interactions or significant differences between the UT, HT and FT treatments for any of the variables studied ( P> 0.05), and only in urinary concentrations and total daily excretion in the urine of thiocyanate (SCN) were there significant differences between the diets containing the LgsRSM and HgsRSM (LgsRSM > HgsRSM; P < 0.01). In ruminal and duodenal digesta there were no detectable quantities of isothiocyanate (ITC), 5-vinyl oxazolididine-2-thione (OZT) or of the nitrile 1-cyano-2-hydroxy-3-butene (NCHB) from any of the diets, but SCN was found in ruminal, but not in duodenal, digesta from the LgsRSM and HgsRSM diets. Compared with giving diets containing the SBM, diets containing LgsRSM and HgsRSM gave significantly higher concentrations of GLDH in serum and significantly lower concentrations of GSH in blood. No detectable quantities of ITC or OZT were found in milk, and only traces of NCHB, but SCN was found from both the LgsRSM and HgsRSM diets, and concentrations and total daily secretions were significantly higher than from the SBM diet.
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