Effects of oral administration of brassica secondary metabolites, allyl cyanide, allyl isothiocyanate and dimethyl disulphide, on the voluntary food intake and metabolism of sheep

Glucosinolates, such as sinigrin, and S-methyl cysteine sulphoxide (SMCO), which are found in forage brassica species have been implicated in the low intakes observed among lambs consuming such diets. To test both the individual and interactive effects of these compounds in sheep, all combinations of the sinigrin breakdown products, allyl cyanide (ACN) and allyl isothiocyanate (AITC; 10 mmol/d), and the SMCO metabolite dimethyl disulphide (DMDS; 25 mmol/d) were orally administered twice daily for 5 weeks to forty sheep offered dried grass pellets ad lib. As well as measuring voluntary food intake (VFI), a number of haematological and clinical function tests were conducted to assess the physiological effects of the compounds. VFI was significantly depressed by both ACN and AITC but not by DMDS. DMDS significantly ameliorated the effects of ACN on VFI (P < 0.001). Concentrations of reduced glutathione in the blood were depressed by ACN and AITC and elevated by DMDS but no significant interactions were evident. Elevated plasma gamma-glutamyl transpeptidase (EC 2.3.2.1) activity on ACN and AITC treatments indicated possible liver damage. DMDS elicited a rise in Heinz bodies to 11% by week 2 but this was not reflected in packed cell volume and blood haemoglobin levels which were unaffected by treatment. The increased Heinz body count caused by DMDS was not further influenced by ACN or AITC. In conclusion, the depressive effects of sinigrin breakdown products on VFI were not compounded by the additional presence of DMDS which, on the contrary, lessened the depression of VFI caused by ACN.