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Endogenous Secretion and Reabsorption of ⁶⁵Zinc in Ruminants as Affected by Zinc Deficiency and Feeding of Ethylenediaminetetraacetate or Cadmium¹

Dairy Science Department and School of Veterinary Medicine, University of Georgia, Athens

ABSTRACT

Using chromic oxide as a nonabsorbed marker, endogenous secretion and reabsorption of ⁶⁵Zn in various segments of the gastrointestinal tract were studied in seven zinc-deficient and six normal calves and in eight deficient and eight normal goats. All were fed a highly digestible low zinc purified diet. The animals were euthanatized 14 days following a single oral dose of ⁶⁵Zn, at which time all the gastrointestinal ⁶⁵Zn was assumed to be of endogenous origin, though the amount present would be reduced by reabsorption. Dry matter digestibility, ⁶⁵Zn, and chromic oxide were determined in each section. Dry matter was absorbed in the rumen of both species with large amounts of secretion into the upper small intestine and reabsorption in the lower small intestine. Zinc-65 was secreted into the rumen and reticulum followed by variable amounts of reabsorption in the abomasum. Large amounts of ⁶⁵Zn were secreted into the anterior section of the small intestine with nearly all of it reabsorbed farther down the small intestine. The feeding of EDTA and cadmium did not have a clear-cut effect on ⁶⁵Zn or dry matter secretion or reabsorption in most sections. Likewise, a zinc-deficiency did not have a marked and consistent influence in most sections. There were appreciable differences in apparent dry matter and ⁶⁵Zn secretion into the upper small intestine between calves which fasted overnight and goats fed three hours prior to sacrifice. It is believed that this effect was due primarily to difference in the length of time since feeding the low residue diet.

¹ Journal Series Paper no. 116, University of Georgia College of Agriculture Experiment Stations, College Station, Athens, and Institute of Comparative Medicine Paper no. 692. Supported in part by Public Health Service Research Grant no. AM 07367 NTN from the National Institute of Arthritis and Metabolic Diseases.