Rumen responses to dietary supplementation with cashew nut shell liquid and its cessation in sheep

Rumen responses to cashew nut shell liquid (CNSL) were evaluated in a feeding study. Four wethers were fed a hay and concentrate diet for 4 weeks (pre-CNSL period), and then fed the same diet supplemented with low and high levels of CNSL for 2 weeks each (L-CNSL and H-CNSL periods respectively). The diet was then reverted to the unsupplemented control diet for another 2 weeks (post-CNSL period). Rumen parameters were monitored in each feeding period. CNSL, regardless of the two levels tested, did not show any adverse effects on total short chain fatty acid concentration and dry matter digestibility in the rumen. Propionate proportion increased in the H-CNSL period, while methane production potential, acetate and butyrate proportions, viscosity, foam formation and its stability, and ammonia concentration decreased. Values of these parameters returned to those in the unsupplemented control period after cessation of CNSL supplementation. Clone library analysis of 16S rRNA genes revealed the following shifts in the H-CNSL period. For bacteria, Firmicutes was frequently detected, while Bacteroidetes and Spirochetes were not. For archaea, Methanobrevibacter wolinii was predominant. These results indicate that CNSL could be a methane inhibitor and propionate enhancer by altering the rumen microbial community.