High grain diets in ruminants: Acidosis and starch digestion

Three experiments were conducted to elucidate the effects of ruminal acidosis on rumen and pancreatic tissue function, and to determine if feeding wet corn gluten feed would alleviate acidosis. An additional experiment was conducted to determine if glucose absorption was a limiting factor of starch digestion in the small intestine in ruminants. In Experiment 1, increasing severity of ruminal acidosis resulted in a decrease in ruminal pH, and an increase in ruminal concentrations of D($-$) and L(+) lactate. Concentration of total organic acids in the rumen increased with increasing severity of acidosis. Blood pH decreased and plasma concentration of D($-$) lactate increased with increasing severity of ruminal acidosis. However, plasma concentrations of L(+) lactate were unchanged. Plasma activities of amylase and lipase were not influenced by increasing severity of acidosis indicating pancreatic tissue damage did not occur. Fractional rates of acetate, propionate and butyrate absorption and liquid passage rate were numerically lower in acutely acidotic lambs versus control lambs for up to 6 months following the acidosis insult. Steers fed wet corn gluten feed had lower dry matter intake variation than steers fed dry rolled corn during days 19 to 24. Over a 132-day feeding period, steers fed 86.5 or 94.5% wet corn gluten feed had lower intakes and daily gains than steers fed dry-rolled corn or 35% wet corn gluten feed, although feed efficiency was not different among treatments. In a metabolism experiment, area below ruminal pH 6.0 was greater over a 24-h period for steers dosed with 100% dry-rolled corn compared with steers dosed with 50% dry-rolled corn:50% wet corn gluten feed, or 100% wet corn gluten feed. In addition, more ruminal VFA accumulated over 24 h for steers dosed with 100% dry-rolled corn. In steers with chronic indwelling catheters, glucose concentration in ileal fluid was greater when glucose was infused into the midjejunum and increased as glucose infusion in both duodenum and midjejunum increased from 0 to 18 g/h. Portal minus arterial concentration difference and net portal flux of glucose were greater when glucose was infused duodenally. When increasing concentrations of glucose were infused duodenally, net portal glucose absorption accounted for 100% of small intestinal glucose disappearance. However, when increasing glucose was infused into the midjejunum, decreasing net portal utilization of glucose was observed and no net portal absorption occurred