Does humate supplementation affect ciliate population and fermentation parameters in the sheep rumen?

. The objective of the study was to examine the effect of supplementing sheep diets with humic substances (HS) on the number of protozoa and short chain fatty acid and methane concentrations in the rumen. The experiment was carried out in three rumen-fistulated sheep. The control (CON) ration was composed of 59.70% hay and 40.30% concentrate. Two experimental diets consisting of the same components were supplemented with two doses of humic substrates, 10 (HS10) or 20 (HS20) g/day/animal. The population of total protozoa and the genera Entodinium and Isotricha in the rumen was the most abundant before feeding (0 h) and decreased 2 and 4 h after receiving the diets. The populations of total protozoa and the genus Entodinum in the rumen were more abundant 2 h after administration of HS10 and HS20 compared to CON. The counts of these groups of protozoa increased 8 h after feeding HS10 compared to CON and HS20. An interaction trend (sampling time × treatment) was detected in terms of the number of Isotricha spp. in the rumen. The postprandial (2 and 4 h) pH of the rumen was lower than 0 h and 8 h after feeding CON and HS. Short chain fatty acid concentration was higher 2 and 4 h after feeding compared to 0 h and 8 h postprandial. An interaction trend was as assessed based on acetic acid levels; the highest was observed 4 h after feeding HS20 and the lowest 8 h after feeding HS10. Butyrate concentration was lower 8 h after feeding compared to 2 and 4 h postprandial levels for sheep fed the CON and HS10 diets. Branched chain acid production was the lowest 8 h after feeding compared to 0 h and 2 h after HS10 administration. An interaction trend was observed for methane levels; the highest was showed 4 h after feeding HS20 and the lowest 8 h after feeding HS10 diets. HS supplemented to sheep diets increased the abundance of total protozoa and the genera Entodinium and Isotricha in the rumen. It seemed that humates could modify the production of acetate and methane in the rumen, as slight increases in these parameters were observed. This suggests that humic substances can intensify methanogenesis in the rumen.