Effect of Ration upon the Intestinal Distribution of Ca, Mg, Na, K and N in Calves

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Abstract
The intestinal distribution of Ca, Mg, Na, K and N was compared in 3-month-old calves fed semipurified, concentrate and concentrate + hay rations. Unabsorbed markers (Cr2O3 or 144Ce) were used to determine net secretion or absorption, or both, of Ca, Mg, Na, K and N along the gastrointestinal tract. All calves were fed constant amounts of their respective ration and an unabsorbed marker for at least 8 days before killing. Calves were killed 4 hours after feeding and their gastrointestinal tracts tied off, removed, divided into sections, and the contents weighed and sampled. A net secretion of Ca, Mg, Na, K and N occurred in the upper small intestine in all calves. Absorption of these constituents was greatest in passage through the small intestine. Few changes occurred in the intestinal concentrations of Ca, Mg and N in passage through the cecum and large intestine. Minimal values of Na and K secretion and absorption were calculated for the lower gut. It was estimated that an average of 133 g of Na were secreted into the upper small intestine daily. During passage through the lower gut, 87% of the net Na absorption occurred in the small intestine and 13% in the cecum and large intestine. The minimal value of K secretion into the upper small intestine was estimated to be 36 g daily. Absorption of K from the small intestine accounted for 90% of the net K absorption from the lower gut. Differences attributable to ration were observed in the ruminal concentrations of Mg and K in the calves fed the semipurified ration. Few concentration differences were evident in the small intestine that could be attributed to ration.