REVIEW OF ZINC TOXICITY WITH SPECIAL REFERENCE
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,
2. Schagel,L.M.Zinpro Zinc Methionine: Its Role in Swine
Rations. Proceedings, American Assn. of Swine Practitioners,
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
5. Puls,R. Mineral Levels in Animal Health; Diagnostic Data.
Sherpa International, P.O. Box
Columbia, V2T, 4X2, Canada.
6. Venugopal,B.,Luckey,T.D.In Metal Toxicity in Man-Trials,
2. Plenum Press, New York,
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.J.,Jrni Small Animal Medicine. 1990. Publication pending.
Lewis J. Runnels, DVM,ADDL Veterinary Diagnostic