Rumen microbial degradation of allyl cyanide as a possible explanation for the tolerance of sheep to brassica‐derived glucosinolates

Abstract

AbstractPrevious 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 μmol ml−1 to 0.36 μmol ml−1 in 100 min) but not in that from sheep fed dried grass (1.0 μmol 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.