Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Animal Science (Animal, Dairy, and Poultry Sciences)

First Advisor

L. Dwain Bunting

Abstract

Steers fed a conventional diet were utilized to determine the effects of various Zn supplements on ruminal distribution of Zn. Treatments consisted of a basal (B) diet (no Zn supplementation) and B supplemented with equal parts of Zn from either a polysaccharide complex of Zn (PC-Zn) or zinc oxide (ZnO). Samples were fractionated into four fractions: a cell-free fraction, a particulate fraction and two microbial fractions. After PC-Zn or ZnO were dosed intraruminally, relative distribution of Zn from each Zn source within each fraction was evaluated up to 8 h postdosing. Cannulated growing lambs were used to study the effects of dietary concentrate level on utilization of Mg and Zn. Treatments consisted of concentrate:forage (C:F) ratios of 14:86, 43:57 and 71:29. Changes in ruminal absorption of Mg and Zn, and intestinal flow of these minerals associated with various fractions of ruminal contents were evaluated across treatments. Harvested ruminal fluid bacteria from cannulated cattle fed diets with normal and high Zn levels were subjected to two treatments, a strong detergent or a protease-acid, to estimate the amount of bacterial Zn released into solution as a result of these treatments. Dietary Zn appeared to become rapidly associated with the microbial and particulate fractions. Further, Zn concentrations in all fractions of whole ruminal contents were higher (P $<$.05) in the PC-Zn supplemented steers compared with the ZnO supplemented steers. Bacterial intestinal Mg and Zn flow increased (P $$.05), but ruminal Zn absorption declined (P $<$.05) with increasing C:F. Results suggest that dietary Mg and Zn became associated with the microbial matter in the rumen to a great extent and that PC-Zn was ineffective in lowering Zn uptake by ruminal microorganisms. Further, microbial incorporation of Zn may lower the amount of Zn available for ruminal absorption and that the extent of this incorporation may increase as dietary concentrate level increases. The availability of microbial Zn postruminally is less certain; although a great proportion of Zn may be released from bacteria when subjected to the acid conditions of the abomasum.

Pages

117

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