RUMEN MICROBIAL-DEGRADATION OF ALLYL CYANIDE AS A POSSIBLE EXPLANATION FOR THE TOLERANCE OF SHEEP TO BRASSICA-DERIVED GLUCOSINOLATES

Previous studies have shown that sheep are relatively tolerant to the prop-2-enyl glucosinolate breakdown product, allyl cyanide (ACN). In order to examine the extent to which this is due to degradation of the toxin in the rumen, the in-vitro stability of ACN in sheep rumen fluid was determined. Gas chromatography of the volatiles in rumen fluid sequentially sampled following addition of ACN revealed a steady reduction in ACN concentration in the rumen fluid of cabbage-fed sheep (1.0-mu-mol ml-1 to 0.36-mu-mol ml-1 in 100 min) but not in that from sheep fed dried grass (1.0-mu-mol ml-1 unchanged after 160 min). In a further experiment the time taken to develop an adapted rumen microbial population was determined by switching sheep abruptly from a grass to a cabbage diet and measuring the 'ACN-degrading potential' of rumen fluid over 29 days. Adaptation was rapid (< 6 days) and could confer tolerance to the effects of ACN to sheep consuming forage brassica crops.