Abstract
Three German Holstein cows with ruminal and duodenal cannulas (Trial 1) and four non-lactating Slovakian White and Black cows with an additional ileal re-entrant cannula (Trial 2) were used to determine the effects of prolonged adaptation periods on rumen fermentation and starch digestibility in the digestive tract. In Trial 1, the cows received a starch rich diet and in Trial 2, either 1.0 or 2.0 kg corn or wheat starch per cow and per day were continuously infused into the duodenum. In Trial 1 feces, rumen fluid and duodenal digesta were sampled after 14, 16 or 21 days and after 35, 37 or 42 days of adaptation, respectively. In Trial 2, the duodenal and ileal nutrient flow as well as fecal excretion were measured without starch infusion in a preperiod, as well as 9 or 23 days after starting starch infusion. In Trial 1, the rumen pH was increased (5.4 versus 5.9; P≤0.05) and the total volatile fatty acid (VFA) concentration was decreased (144.1 mmol/l versus 134.3 mmol/l; P≤0.01) with prolonged adaptation period. The ruminal digestibility of nearly all nutrients increased numerically, but only that of OM for the diet containing corn increased significantly (45.8% versus 48.3%; P≤0.05) after longer adaptation time. In Trial 2, starch digestion in the small intestine decreased with increasing amounts of starch in the intestine (corn starch: from 71.4 to 50.3%; P≤0.001; wheat starch: from 73.8 to 53.1%; P≤0.001) and was increased by 1.5–2.8 percentage units ( P≤0.05) after prolonged adaptation period. The decreased starch digestibility in the small intestine with increased amounts of starch in the duodenum was not totally compensated for in the large intestine. The high amounts were still 16.4 percentage units (corn starch) and 18.1 percentage units (wheat starch) less digested than the small amounts. The longer adaptation period had small but significant ( P<0.05) effects on the starch digestibility in the total intestine.
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