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OCR for page 34
FO OD ADDITIVE S
Information on the effects of food additives in cats is
scarce because routine toxicity testing is rarely con-
ducted on this species. Where a nonroclent mammal is
required for testing, usually the dog or pig (or possibly
ferret) is chosen rather than the cat. Avoidance of the cat
as a test animal is probably partly due to its reputation as
a finicky eater. More important, however, is the cat's
unusual sensitivity to some chemicals because of differ-
ences in the pathways of metabolism of these com-
pounds in the cat compared with other animals. Conse-
quently, results obtained from screening tests might not
be readily applicable to other mammals (including
man) and could give an unrealistically severe assessment
of the toxicity of an additive.
BENZOIC ACID AND RELATED
COMPOUNDS
Benzoic acid and its salts are used in human foods as
preservatives, particularly as antifungal agents. Cats
are much more susceptible than other mammals to these
compounds because of their reduced ability to detoxify
them. In most species benzoic acid derivatives are me-
tabolized by dual pathways of conjugation with glycine
and glucuronic acid to produce hippuric acid and ben-
zoyl glucuronate, respectively (Bridges et al., 1970~.
The glucuronide pathway, which has the greater capac-
ity, is defective in the cat and only the glycine pathway
is operative (Williams, 1967~. This defect is responsible
for cats' hypersensitivity to other phenolic compounds,
including aspirin. Bedford and Clarke (1972) found that
the highest continuous daily intake of benzoic acid that
could be tolerated for 15 days was 200 mg/kg body
Other Food
Constil;uents
weight (BW). An intake of 300 mg/kg BW/day caused
mild hyperesthesia from which the cat recovered, but
higher doses caused aggression, hyperesthesia, and
death. Although it is theoretically possible to stipulate a
safe concentration of benzoic acid on the basis of these
results, in practice the use of this additive in cat foods is
not advisable because of the low margin of safety, the
possibility of overdispensing or inadequate mixing re-
sulting in high concentrations in certain batches, and its
relatively poor preservative action at the concentrations
permitted by the observed no-adverse-effect level. Ben-
zyl alcohol poisoning has also been reported in cats (Cul-
lison et al., 1983) that had received lactated Ringer's
solution containing benzy! alcohol as a preservative. In
the body the alcohol is rapidly oxidized to benzoic acid
and hence is toxic to the cat. Because of the problems
associated with benzoic acid in the cat, safer and more
effective alternatives to this chemical are recommended
for use in pet foods. Sorbic acid produced no adverse
effects in cats when fed at concentrations up to 2 percent
of a canned meat-based diet (Bedford and Clarke,
1973~. The effective antifungal concentration Is only
about 0.2 percent. Phillips et al. (1978) found that ra-
dioactively labelled p-hydroxybenzoic acid, when fed to
cats at doses up to 130 mg/kg, was rapidly excreted in
the urine. Only one major metabolite was identified, p-
hydroxyhippuric acid. The same results were obtained
in animals pretreated with the compound in the diet for
28 days. Studies with the ethyl and n-propyl esters
showed a similar route of metabolism except that in this
case two major metabolites were identified, p-hydroxy-
hippuric acid and free p-hydroxybenzoic acid. As with
sorbic acid, the tested intakes of these compounds are
sufficient to allow their use in foods. The concentrations
used are typically up to 0.2 percent on dry matter or
about 50 mg/kg BW/day for an adult cat.
34
OCR for page 35
COLOR
Cats appear to possess limited color perception (De
Reuck and Knight, 1965); however, a variety of artificial
and natural colorants are added to cat foocis to enhance
human appeal for such products. Many colorants (e. g.,
caramel) are used on the basis of work carried out in
other species (CRC, 1972~. Therefore, this section only
considers colorants where direct data on the cat are
available.
One of the few long-term toxicity tests conducted in
the cat is a teratogenicity study of the food color ama-
ranth (F. D, and C Red No. 2) reported by Khera et al.
(1976) . Cats were given doses of amaranth up to 265 ma/
kg BW/day for a time period extending from 0 to 22 days
before conception to days 61 to 62 of gestation. Kittens
were then delivered by Caesarean section. There was no
evidence of embryotoxicity at any dose level. Maternal
indices (including incidences of pregnancy, nonpre-
gnancy, and abortion) also showed no adverse effects
related to amaranth. For this color the cat study gave
results similar to those obtained in other species, includ-
ing the dog.
Amaranth is one of the azo group of colors that, on
reduction in the body, yield aniline compounds. These
are well-known inducers of Heinz body formation in an-
imals. Heinz bodies are small inclusion particles in
erythrocytes that result from the oxidative degradation
of hemoglobin, and the cat erythrocyte is reported to be
particularly sensitive to the induction of these inclu-
sions. Cats have therefore been used to test the effects of
several azo colors on Heinz body induction, namely am-
aranth (JECFA, 1975), tartrazine (JECFA, 1964),
azorubine, also known as carmoisine JECFA, 1974b),
and sunset yellow (Khera and Munro, 1979~. Doses up
to 1 g/day were given for periods up to 35 days. Negative
results for Heinz body formation were obtained for all
colors tested.
Another color that has been tested in cats is titanium
dioxide. This is a white pigment possessing considerable
"coloring power," which is used widely throughout the
food industry. Two cats were fed 3 g/day of technical
gratle titanium dioxide for 390 days. Two other cats re-
ceivec] the same intake for 175 and 300 (lays. No adverse
effects were seen during the trial or on histopathological
examination RECTA, 1970~.
SODIUM NITRITE
Sodium nitrite is a widely employed human food ad-
ditive used particularly as an antimicrobial agent and
also as a color stabilizer or fixative, especially in meat
Nutnent Requirements of Cats 35
products, where it reacts with the heme pigments
myogiobin and hemoglobin to form stable nitrosyl de-
rivatives. A considerable amount of research has been
conducted on this additive, and there is a report of a
feeding trial in one cat that received an average of 39 mg
of sodium nitrite daily over 105 days without ill effects
RECTA, 1974a). This is equivalent to an intake of ap-
proximately 105 mg/kg body weight/day for an adult (4
kg) animal.
PROPYLENE GLYCOL
(1,2 PROPANEDIOL)
Propylene glyco! is a low-molecular-weight alcohol
used in the control of water activity in human and pet
foods. The biological effects of propylene glycol have
been the subject of general reviews (Morris et al., 1942;
RucIdick, 1972), but no direct studies have been pub-
lished for cats. However, it is known that the lipids in
cat erythrocyte are sensitive to oxidants and increased
numbers of Heinz bodies have been observed in cats
given diets containing propylene glyco} (K. C. Hayes,
Brandeis University, personal communication, 1985~.
Thus, the use of high levels of propylene glyco] might be
expected to decrease the life of the erythrocyte resulting
in hemolytic anemia in cats.
OTHER FOOD ITEMS
There are few incidences in which food itself has been
reported to cause adverse effects in cats. An obvious ex-
ception to this is liver, but this has already been dis-
cussed in the section on vitamin A. Allergic reactions to
food have been reported in the cat, but even here the
scale of the problem is difficult to assess and incidences
between 1 and 30 percent have been suggested. The sites
usually affected are the skin and alimentary tract. A1-
though a detailed discussion of the problem is outside
the scope of this publication, the subject has been re-
viewed recently by Stogdale et al. (1982~.
Onion poisoning has been described in the cat by Ko-
bayashi (1981), who reported a hemolytic anemia and
an increase in Heinz bodies in cats that had consumed
onion soup. Hemoglobinuria also occurred when large
quantitites of soup were ingested. Clinical signs disap-
peared with the cessation of onion feeding and the poi-
soning was not considered to pose a clinical problem un-
less consumption was excessive or prolonged.
One further item worth mentioning under this head-
ing is the possible risk of poisoning from cocoa and re-
lated products. Although this has not been reported in
OCR for page 36
36 Nutnent Requirements of Cats
cats, it is well documented in dogs and presents a risk of
intoxication from what would normally be consiclered a
harmless material. The toxic principle is the methylxan-
thine derivative theobromine and the signs of poisoning
are vomiting, diarrhea, sudden collapse, and death.
The oral LDso for cats is 200 mg/kg BW and, as cocoa
.
contains 1.5 to 2.0 percent theobromine (Sutton, 1981),
it would theoretically need only 40 to 50 g to provide a
potentially lethal dose. Chocolate has a much lower
theobromine content of around 0.2 percent (Glauberg
and Blumenthal, 1983) and is therefore less of a hazard.
Representative terms from entire chapter:
heinz body
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