Absorption of zinc from small and large intestine of calves.

Calves fed a high-zinc diet were used to study zinc absorption from various sections of the small intestine. Absorption was determined by measuring zinc-65 in various tissues and plotting the tissue concentrations against dosing site, expressed as percentage of intestinal length. Zinc absorption, per unit of intestinal length, was similar throughout the small intestine and was as great in the distal as in the proximal end. Apparently, early researchers using isolated loops and everted sac techniques failed to recognize rate of digesta passage and tissue homeostasis as major factors associated with zinc uptake when they concluded that the duodenum was the primary site of zinc absorption. The data show that the duodenum is not the major site of zinc absorption in calves regardless of dietary zinc. In a separate experiment, zinc-65 was injected directly into the large intestine of calves fed a low zinc diet. Only about 2% of total zinc absorption was from the large intestine.