The effect of plant alkaloids on in vitro rumen microbial fermentation

Crude alkaloid extracts from green Italian Ryegrass differed from those extracted from the ensiled grass with particular respect to the perloline moiety. Free perloline and crude alkaloid extracts from both silage and grass inhibited the production of volatile fatty acids in the fermentation of glucose by rumen microbes. With silage as fermentation substrate alkaloid extracts from silage and from grass (0.200 mg/l) caused a decrease in both substrate utilization ( P< < 0.01) and proportion of methane in the gas phase ( P< < 0.01). Molar proportions of acetate were also significantly decreased ( P < 0.01) with a corresponding increase in the proportion of propionate ( P < 0.01). These effects were not observed when grass nuts were used as the fermentation substrate. The results suggest that it is not the alkaloids per se that affect rumen microbial metabolism.