Physicochemical stressors and mixed alkaloid supplementation modulate ruminal microbiota and fermentation in vitro.

The drop of ruminal pH and heat are common physicochemical stressors challenging ruminal microbiota, nutrient digestion and cattle performance. We characterized the ruminal microbiota and digestive activity in response to different pH (6.0 and 6.6) and temperature (39.5 and 42 °C), as well as established the effective dose of alkaloid supplementation (0, 0.088 and 0.175% of feedstock DM) to modulate ruminal fermentation under these conditions. The acidotic condition decreased microbial diversity and abundances of minor bacterial families whereas most of the highly abundant families like Lactobacillaceae, Prevotellaceae, and Bifidobacteriaceae thrived under the stress. Abundances of all three methanogenic archaea taxa detected increased with heat, as did methane production. However, while Methanomassiliicoccaceae benefited from the low pH, Methanomicrobiaceae diminished and methane production decreased. The low dose of alkaloid addition shifted the fermentation to more propionate and less acetate and the high dose decreased methane and ammonia concentration under the low pH. In conclusion, physicochemical stressors shape the microbial community and function. Mixed alkaloid supplementation facilitates the activity of rumen microbial community under acidotic stress.