There have been recent reports of the efficacy of adding more bioavaili­able zinc compounds in a chelatedform to swine rations to enhance treatment of porcine enteropathies, and to improve performance (1)(2). When correctly used, there is little, if any toxic hazard from inorganic or chelated zinc compounds. (8)

Most species are relatively toler­ant to zinc. Rats, pigs, and poultry tolerate dietary levels of 1000 'to 2000 ppm without adverse effects (3). Rats, poultry, pigs, sheep, cattle and man exhibit considerable toler­ance depending on the nature of the diet, particularly its content of Ca, Cu,Fe,Cd with which it interacts to affect utilization. Toxic levels of dietary Zn are only meaningful with respect to these interacting elements when the status of the diet and the animal is known and defined (4).

"Ruminants are more susceptible to Zn intoxication than mono-gastric animals (6)."

Toxicity is also dependent on the form of zinc; greater than C.1°o die­tary zinc as lactate or carbonate is toxic and greater than 0.5% zinc as oxide is toxic.  Ruminants are more susceptible to Zn intoxication than monograstric animals (6).  Weanling pigs fed for several weeks on diets containing 1000 ppm zinc, either as the sulfate or carbonate suffered no obvious toxic effects.  At higher zinc levels there was depressed growth and appetite, arthritis and internal hemorrhages.  At dietary levels of 4000 to 8000 ppm, mortality was high, raising the dietary Ca lev­el from 0.7 to 1.1% had a protective effect against toxic effects at 4000 ppm of Zn0(5).  Zinc induced hemolyt-ic anemia and internal hemorrhage has been reported in dogs that consumed pennies containing high levels of zinc alloy minted since 1983(3)(7)(9).

Signs of toxicity include growth depression, gastrointestinal inflam­mation, arthritis and hemorrhage in auxiliary spaces.  There is an in­creased incidence of osteochondrosis. Serum Ca and liver Felevels are re­duced.  Serum alkaline phosphataseactivity is elevated.  Increased Ca supplementation raises the Zn re­quirement and storage in the liver. Increased Zn supplementation reduces Cu storage in the liver.  High Ca, soy-protein and phytate enhance Zn deficiency (5).

Diagnoses of zinc toxicosis is based on elevated zinc levels in se­rum or liver.  At least 2 ml of clear serum, separated from the clot in a screwcapped glass tube should be sub­mitted to the laboratory.  Since rub­ber contains high levels of zinc, it is important to not let the serum come in contact with rubber tipped syringe plungers or rubber stoppered tubes either during the collection or shipping.  Ten grams of liver can be submitted from necropsied animals suspected of zinc toxicity or deficiency.

1. Daniels, G.M. Porcine Enteropa-thies-Relationship of Pathogenesis to Zinc.  In brochure "The Performance of ZINPRO, Zinc Methionine in Swine Production, ZINPRO Corp. Edina, Minn., 1990, Pg. 5.

2. Schagel,L.M.Zinpro Zinc Methio­nine: Its Role in Swine Rations. Proceedings, American Assn. of Swine Practitioners, 1990.pg. 99.

3. Ogden,L., Edwards, W.C., Nail, N.A. Zinc Intoxication in a Dog From the Ingest ion of Copper Clad Zinc Pennies. Vet. Hum. Toxicol.30 (6) Dec. 1988, 577.

4. Underwood, E.J. Zinc Toxici­ty. In Trace Elements in Human and Animal Nutrition, 4th ed. Academic Press, New York, 1977.230-232.

5. Puls,R. Mineral Levels in Animal Health; Diagnostic Data. Sherpa In­ternational, P.O. Box 2256.Clear-brook British Columbia, V2T, 4X2, Canada. (Trinity Western University Press, Canada). 1988.

6. Venugopal,B.,Luckey,T.D.In Metal Toxicity in Man-Trials, 2. Plenum Press, New York, 1979. 72-76.

7. Latimer,K.S., Jain, A.V., Inglesby,N.B.,Clarkson,W.D., John-son, G.B. Zinc Induced Hemolytic Ane­mia Caused by Ingest ion of Pennies by Pup. JAVMA, 195, (1) July 1, 1989, 77.

8. Pritchard,G.E., Lewis, G., Wells, A.H.,Stopforth, A. Zinc Toxicity, Copper Deficiency and Anemia in Swell-fed Pigs. Vet. Rec., Nov. 23, 1985, 545-548.

9. Robinson, F.R., Mason, P.M., Ful­ton, R.H., Martinez,B.S.,Everson, R.J.,Jrni Small Animal Medicine. 1990. Publication pending.

Lewis J. Runnels, DVM,ADDL Veterinary Diagnostic