Effect of abomasal carbohydrates and live yeast on measures of postruminal fermentation.

Two studies were conducted to evaluate the effects of abomasal carbohydrate infusion on nutrient digestibility and fecal measures. In Exp. 1, 5 Holstein steers were assigned to a Latin square with 1-wk periods and were abomasally infused on a single day at the end of each period with water alone, a single pulse dose of water with 1 g/kg BW oligofructose or cornstarch, or 4 pulse doses of water with 0.25 g/kg BW oligofructose or cornstarch administered every 6 h. Total tract nutrient digestibility was not affected by treatment except for a tendency for a decrease in starch digestibility in response to the 1 g/kg BW dose of cornstarch ( < 0.10). Compared with the control, both oligofructose and starch infusions caused similar decreases in fecal pH ( < 0.05) and increases in fecal short-chain fatty acids ( ≤ 0.01) measured 12 h after the first infusion, with the single 1 g/kg BW infusions causing a greater magnitude of pH change compared with the four 0.25-g/kg BW infusions ( < 0.01). All treatments increased concentration of fecal lipopolysaccharide compared with the control for at least 1 time point following the infusion ( < 0.05), with a greater increase observed for the 0.25 g/kg BW infusions of oligofructose compared with the other treatments ( < 0.05). Results of Exp. 1 indicate that both oligofructose and cornstarch infusions increased carbohydrate fermentation in the intestines and can be used as a method to evaluate the impact of excessive intestinal fermentation on intestinal health. In Exp. 2, 6 Holstein steers received abomasal pulse doses of 0 (control) or 10 g/d live var. (SB) according to a crossover design with 18-d periods. Abomasal infusions of 4 pulse doses of 0.25 g/kg BW oligofructose administered every 6 h were conducted on d 16 of each period. During the baseline period prior to the oligofructose challenge, there were no effects of SB on fecal measures except for an increase in apparent total tract NDF digestibility ( < 0.05), suggesting that SB increased intestinal fiber fermentation. During the oligofructose challenge, SB increased fecal score ( = 0.03) and tended to reduce fecal short-chain fatty acids ( = 0.10). Results of Exp. 2 suggest that abomasal SB modestly stabilized the intestinal environment during increased carbohydrate fermentation.