Zinc Absorption, Metabolism, and Endogenous Excretion in Zinc-Deficient and Normal Calves over an Extended Time

¹ Department of Animal and Dairy Science, University of Georgia, Athens 30602

Zinc metabolism was studied in Zn-deficient and control Holstein calves over a 2-mo period following a single oral or i.v. ⁶⁵Zn dose. In both orally and i.v. dosed animals, all gastrointestinal tissue sections from Zn-deficient animals contained more ⁶⁵Zn than comparable tissues of controls. Contents of proximal small intestinal sections of Zn-deficient calves contained more ⁶⁵Zn 8 to 10 wk after dosing than did those from controls; however, the reverse occurred in the distal small intestine, cecum, and large intestine. With both dosing methods, Zn-deficient calves retained more ⁶⁵Zn throughout the study. Daily ⁶⁵Zn, excretion rate as a percentage of that retained declined for 6 wk after dosing, indicating a constantly increasing biological halflife. For deficient calves, the biological half-life was about 500 d in the later weeks of the experiments. In orally dosed, Zn-deficient animals, specific activity of fecal ⁶⁵Zn exceeded that of serum Zn throughout the study. This shows a shortcoming in the basic assumption of measuring endogenous Zn loss from fecal and serum specific activities and total fecal stable Zn. Thus, endogenously excreted Zn is not representative of that remaining.

Key Words: zinc metabolism • endogenous zinc excretion

Submitted on February 28, 1991
Accepted on May 31, 1991