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⁶⁵Zn Tissue Distribution in Lactating Holstein Cows Fed Normal and Low-Zinc Practical Diets^{1, 2,}

University of Georgia, Athens 30602

Abstract

Following oral dosing, tissue distribution of ⁶⁵Zn and zinc specific activity were studied in first-lactation Holstein cows fed a low-zinc diet (16.6 ppm Zn) and the same diet supplemented with ZnO to provide 39.5 ppm total zinc in the ration dry matter. Low dietary zinc increased (P<.05–P<.01) ⁶⁵Zn and zinc specific activity in all body tissues studied, except rib cartilage, 17 days after dosing with the effects greater in the biologically more active tissues. A part of the increased retention was due to higher ⁶⁵Zn absorption. All sections of the gastrointestinal tract tissues and digestive tract contents from the low-zinc fed cows contained more ⁶⁵Zn and had higher zinc specific activity than in controls (P<.01). The ⁶⁵Zn content of whole blood, plasma, red blood cells (RBC) and the zinc specific activity in plasma and RBC of the low-zinc fed cows were more than twice that of controls. Peak ⁶⁵Zn blood levels were reached on or prior to day 2 after dosing, then declined moderately until day 14. In RBC, ⁶⁵Zn of the low-zinc cows increased sharply to day 7 then leveled off, whereas, that in RBC of control cows was considerably lower and remained at a constant level.

¹ This study was supported in part by Public Health Service Grant No. AM-07367-NTN from the National Institute of Arthritis and Metabolic Diseases.

² The authors thank Kraft Foods Company of Garland, Texas, for the dried whole whey and Dawe's Laboratories, Inc., of Chicago, Illinois, for the vitamins A and D₃. Appreciation is extended to J. C. Brown, Mrs. D. E. Fowler, P. Randall Fowler, D. M. Futch, A. L. Glenn, Jr., S. O'Steen, K. R. Roberts, R. C. Watson, Jr., and H. R. Young, Jr. for technical assistance.

³ Department of Dairy Science.

⁴ Department of Medicine and Surgery.