Rate of Passage of Calcium-45 and Yttrium-91 along the Intestine, and Calcium Absorption in the Laying Fowl

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Abstract
The passage of 45Ca and yttrium-91 (91Y) along the gastrointestinal tract of the laying fowl was compared by dosing either the crop or the duodenum with a double tracer dose. Passage time in the crop and along the intestinal tract was similar for both isotopes but 45Ca appears to have moved more rapidly than 91Y out of the stomach. The passage rate was highest in the duodenum and decreased progressively down the intestine. Outflow of 45Ca from the intestine to the blood was rapid during the first 30 minutes after the duodenal administration, by which time the isotope hardly reached beyond the jejunum. The outflow appears to have slowed down considerably after 30 minutes, as also indicated by the specific activity of 45Ca in blood plasma. It was concluded that the most effective site of calcium absorption in the laying hen is the jejunum. The possible errors in the determination of absorption with the aid of unabsorbed markers, are discussed.