Original article Propionate uptake by rumen microorganisms: the effect of ruminal infusion

Abstract — We assessed the ability of rumen microbes to significantly incorporate propionate when they are subjected in vivo to no infusion, long-term infusion of minerals, and short- and long-term in-fusion of high amounts of propionate. Four ruminally cannulated sheep fed 1000 g hay (8 meals per d) were used in a 4 × 4 Latin square design. The treatments consisted of no infusion (C), ruminal infu-sion of propionate (86 g·d–1) for 1 (P1) and 7 d (P7), and of minerals for 7 d (M7). The infusion of pro-pionate increased its ruminal molar percentage from 19 (C, M7) to 32 % (P1, P7). Ruminal pH, osmolality, ammonia concentration, and protozoa counting were not or were poorly affected by the treatments. Rumen contents (100 mL liquid + 100 g solid) were incubated at 39 oC in anaerobic flasks containing artificial saliva, (NH4)2SO4, ground hay, and 0.45 µCi [2-14C] propionate. After 6 and 16 h, clarified fermenter fluid, liquid-associated protozoa, and liquid-associated bacteria considered as representative of total bacteria were separated by fractional centrifugations. Microbial pellets were washed with saline before 14C determination. In flasks, pH, osmolality, gas, volatile fatty acid (VFA) production, ammonia concentration, protozoal counting and the amount of 14C in clarified fermenter fluid, liquid-associated protozoa and liquid-associated bacteria were similar among the treatments. Between 6 h and 16 h, the amount of 14C decreased in the clarified fermenter fluid, and increased i