Uptake of zinc from zinc sulfate and zinc proteinate by ovine ruminal and omasal epithelia

¹ Department of Animal Science and Interdepartmental Nutrition Program, North Carolina State University, Raleigh 27695-7621
² Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061-0306

^* To whom correspondence should be addressed. E-mail: Jerry_Spears{at}ncsu.edu.

	Abstract

Uptake and transport of Zn from ⁶⁵Zn-labelled ZnSO₄ and Zn proteinate (ZnProt) by ruminal and omasal epithelium were examined using a parabiotic chamber system. Uptake was measured during a 4-h incubation with 10, 20, or 200 µM Zn as ZnSO₄ or ZnProt in the mucosal buffer (pH 6.0, Krebs-Ringer phosphate). Zinc uptake and transport were also evaluated following simulated ruminal digestion. Buffered ruminal fluid contained a feed substrate and 10 or 200 µM added Zn as ZnSO₄ or ZnProt. In a preliminary experiment, uptake of Zn by omasal tissue was very low, thus remaining experiments were conducted solely with ruminal epithelium. Incubations to determine the effect of time on Zn uptake from mucosal buffer containing 20 µM added Zn as ZnSO₄ or ZnProt resulted in increased (P < 0.01) Zn uptake as incubation time increased from 30 to 240 min. Zinc uptake was also greater (P = 0.02) from mucosal buffer containing ZnProt compared to ZnSO₄. Zinc uptake from incubations containing 10 or 200 µM was affected by source x concentration (P = 0.05) and concentration x time (P < 0.01) interactions. With 10 µM Zn, uptake was not influenced by Zn source, whereas when 200 µM Zn was added, Zn uptake from ZnProt was greater than from ZnSO₄. Increasing incubation time resulted in increased Zn uptake with 200 µM Zn in the mucosal buffer; however with 10 µM Zn, uptake did not change after 30 min. Following simulated ruminal fermentation, the proportion of Zn in a soluble form was influenced by a source x concentration interaction (P = 0.03). After 18 h of incubation, the proportion of Zn that was soluble was not different between ZnProt and ZnSO₄ in buffered ruminal fluid that contained 10 µM added Zn, but was greater for ZnProt with 200 µM Zn in the incubation. Zinc uptake from the aqueous fractions of simulated ruminal digestions containing 200 µM added Zn was greater (P < 0.01) than from those containing 10 µM added Zn. Zinc transport, based on detection of ⁶⁵Zn in serosal buffer, did not occur in any of the experiments. Results of the current experiments suggest that absorption of Zn into the bloodstream does not occur from ruminant forestomach; however, Zn uptake occurs in ruminal tissue and is greater from ZnProt than from ZnSO₄.

Key Words: rumen, omasum, parabiotic, proteinate, zinc