Page 232 - Small Animal Clinical Nutrition 5th Edition

Food Safety 235

Most foodborne metal toxicities in dogs and cats involve cult to correlate with onion ingestion because it occurs several
VetBooks.ir lead, zinc, cadmium and arsenic.These agents cause a variety of days postingestion. Clinical signs related to moderate Heinz
body anemia have occurred in dogs consuming relatively small
clinical syndromes depending on age, dose ingested and length
amounts (5 to 10 g of onions/kg body weight) of raw, cooked
of exposure. The specifics of metal toxicities are well described
in several veterinary toxicology textbooks and are beyond the or dehydrated onions (Harvey and Rackear, 1985; Ogawa et al,
scope of this chapter. 1986). In one study, consumption of approximately 30 g of raw
The tendency of metals to accumulate in plants and animals onions/kg body weight for three consecutive days produced
has ramifications for the manufacture of commercial pet severe anemia, erythrocyte Heinz bodies and hemoglobinuria
foods. Several studies have been conducted to quantify such in all dogs fed onions (Ogawa et al, 1986). One animal devel-
accumulations. In one study, researchers analyzed 28 brands oped severe icterus and died on Day 5.
of commercial dog food and seven brands of cat food and Cats are prone to developing erythrocyte Heinz bodies after
found that average levels of lead, arsenic and cadmium were exposure to many chemicals in food (Jain, 1993; Hickman et al,
1.26, 0.37 and 0.22 ppm, respectively (Edwards et al, 1979). 1990; Christopher et al, 1989). Likewise, Heinz body anemia
A later study of 35 dog foods and 13 cat foods found the aver- has occurred in cats after consumption of onions (Kobayashi,
age levels of lead, cadmium and zinc were 0.88, 0.80 and 1981). Baby food or other foods containing similar amounts of
122.0 ppm, respectively (Mumma et al, 1986). These studies onion powder should not be fed to cats because of Heinz body
confirm that nontoxic levels of metals may be present in some formation and the potential for development of anemia, espe-
pet foods; however, their presence at these levels would not cially with high food intake.Cats with concurrent oxidative dis-
support a diagnosis of metal toxicity. Instead, a definite diag- eases may develop additive hemoglobin damage when fed baby
nosis must be based upon finding toxic levels in the food that food containing onion powder (Robertson et al, 1998).
correspond to elevated levels in the patient’s tissues, such as Garlic (Allium sativum) is also a member of the onion fami-
blood, liver and kidney. ly. Long-term exposure to garlic and garlic extracts caused ane-
mia, contact dermatitis and asthmatic attacks in dogs
Other Sources (Poppenga, 1995). Eccentrocytosis appears to be a major diag-
SUPPLEMENTS nostic feature of garlic-induced hemolysis in dogs. The con-
Many people supplement their own food with vitamins, stituents of garlic have the potential to oxidize erythrocyte
herbal remedies and other items purchased at health food membranes and hemoglobin, inducing hemolysis associated
stores. Well-meaning pet owners likewise think that what is with the appearance of eccentrocytes in dogs.Thus, foods con-
good for them is also good for their pets. Unfortunately, this taining garlic should not be fed to dogs (Lee et al, 2000).
practice fails to consider species and dose differences. Cats, in
particular, may be adversely affected by medications considered CHOCOLATE
safe for people. Certainly, vitamin A and D toxicity is well doc- Pets today are often fed “people” food. One delicacy that has
umented. It is also known that many herbal remedies cause potential to cause toxicity is chocolate. Chocolate products con-
adverse effects in people and animals (Poppenga, 1995; tain variable amounts of theobromine, a potent cardiovascular
Remillard and Wynn, 2005). Therefore, the safety of other and central nervous system stimulant (Clark et al, 1981).
“natural” supplements such as aloe, ginseng root, eucalyptus, Although pet owners might believe that chocolate is innocu-
ginger and oil of wintergreen has yet to be established for dogs ous, one poison control center documented six cases of choco-
and cats. As the investigation of the clinical case proceeds, the late poisoning in dogs during a single year (Hornfeldt, 1987).
veterinarian should ask the owner how and why the animal’s Signs such as vomiting, diarrhea, panting, nervousness, excite-
food is being supplemented with these substances. ment, tremors, tachycardia, cardiac dysrhythmias, coma, con-
vulsions and sudden death may appear in four to 15 hours after
ONIONS AND GARLIC ingestion (Hornfeldt, 1987; Gauberg and Blumenthal, 1983;
Owners may also supplement a pet’s food with onions or gar- Hooser, 1984; Sutton, 1981). Renal damage may occur in
lic. Onions derive part of their flavor from n-propyl disulfide, severe cases.
which is toxic to the erythrocytes of several species (Jain, 1993). The toxic dose of theobromine has been reported to be greater
In 1990, a phenolic compound was extracted from onions that than 200 mg/kg body weight (Hornfeldt, 1987). However, a
increased methemoglobin concentrations and caused the for- springer spaniel died after ingestion of two lb of milk chocolate,
mation of Heinz bodies in canine erythrocytes (Miyata, 1990). corresponding to a dose of only 92 mg of theobromine/kg body
Onions may injure the lipid membranes of erythrocytes and weight (Gauberg and Blumenthal, 1983). Based on this case,
irreversibly denature hemoglobin (Jain, 1993). These changes consumption of one typical 1.55-oz. milk chocolate bar (93 mg
result in Heinz body formation, hemolytic anemia and hemo- theobromine)/kg body weight could produce clinical signs and
globinuria. The most common cause of Heinz body hemolysis possibly death (Hooser, 1984). Unsweetened baking chocolate
in dogs is related to ingestion of onions. Although the toxicity also contains high levels of theobromine (450 mg/oz.) and has
has been known for more than 50 years, animal owners still been implicated in cases of toxicity (Hooser, 1984). Finally, dogs
unknowingly feed onions to dogs as part of table food or inten- have also been poisoned by ingesting cocoa powder (1 to 3%
tionally as a supplement. The hemolytic episode may be diffi- theobromine) (Sutton, 1981).