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The role of dietary omega-3 and omega-6 essential fatty acids in the nutrition of dogs and cats: A review

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Omega-3 and omega-6 fatty acids are essential in all mammalians for normal growth and prevention of several diseases. Because of the seed oil production tendencies and the feeding techniques of farm animals, in the Western countries, diets for humans as well as homemade diets for dogs and cats are usually very high in omega-6 and low in omega-3 fatty acids. Several studies have shown that an optimal omega-6/omega-3 fatty acid ratio (about 6 to 1) in the diet of dogs and cats may reduce the incidence of some diseases, such as cancer and sudden cardiac death. Furthermore, the use of fatty acid supplements has proved to be beneficial in the treatment of several pathogenic conditions, such as chronic inflammatory diseases, atopy, chronic renal insufficiency, and some types of cancer. Therefore, particular attention should be paid to the type and quantity of fat sources that are used when diets for dogs and cats are formulated, in order to assure the optimal amount and balance of omega-3 and omega-6 fatty acids in the food.
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1
The role of dietary omega-3 and
omega-6 essential fatty acids in the
nutrition of dogs and cats: a review
1 DIMORFIPA, Università di
Bologna, Ozzano Emilia, Italy
2 Scottish Agricultural College,
Edinburgh, United Kingdom
Indirizzo per la corrispondenza:
Dr. Giacomo Biagi
DIMORFIPA
via Tolara di Sopra 50
40064 – Ozzano Emilia (BO), Italy
Tel: +39-051-2097363
Fax: +39-051-2097373
E-mail: gbiagi@vet.unibo.it
MONOGRAFIA
B
IAGI
G.1,M
ORDENTI
A.L.1,
C
OCCHI
M.2,M
ORDENTI
A.1
PROGRESS IN NUTRITION
VOL.6,N.2,000-000,2004
TITOLO
Il ruolo degli acidi
grassi essenziali
omega-3 e omega-6
nell’alimentazione del
cane e del gatto:
una rassegna
KEY WORDS
Dog, cat, essential fatty acids,
omega-3, omega-6
PAROLE CHIAVE
Cane, gatto, acidi grassi essenziali,
omega-3, omega-6
Summary
Omega-3 and omega-6 fatty acids are essential in all mammalians for nor-
mal growth and prevention of several diseases. Because of the seed oil pro-
duction tendencies and the feeding techniques of farm animals, in the
Western countries, diets for humans as well as homemade diets for dogs
and cats are usually very high in omega-6 and low in omega-3 fatty acids.
Several studies have shown that an optimal omega-6/omega-3 fatty acid
ratio (about 6 to 1) in the diet of dogs and cats may reduce the incidence
of some diseases, such as cancer and sudden cardiac death. Furthermore,
the use of fatty acid supplements has proved to be beneficial in the treat-
ment of several pathogenic conditions, such as chronic inflammatory dis-
eases, atopy, chronic renal insufficiency, and some types of cancer. There-
fore, particular attention should be paid to the type and quantity of fat
sources that are used when diets for dogs and cats are formulated, in order
to assure the optimal amount and balance of omega-3 and omega-6 fatty
acids in the food.
Riassunto
L’apporto alimentare di acidi grassi della serie omega-3 e omega-6 è essen-
ziale nei mammiferi al fine di assicurarne il corretto accrescimento e ridur-
re l’incidenza di alcune patologie. A causa delle odierne tendenze produtti-
ve nel settore delle piante oleaginose e delle moderne tecniche di alimenta-
zione degli animali da reddito, nei paesi occidentali, le diete dell’uomo, così
come quelle preparate in casa per cani e gatti, sono generalmente ricche di
acidi grassi omega-6 e povere di omega-3. Numerose ricerche hanno di-
mostrato che un rapporto ottimale tra acidi grassi omega-6 e omega-3 (in-
torno a 6 a 1) nella dieta di cani e gatti può ridurre l’incidenza di alcune
patologie, quali alcuni tumori e la morte cardiaca improvvisa. Inoltre, l’im-
piego di supplementi alimentari contenenti acidi grassi essenziali può risul-
tare di aiuto nel trattamento di diverse condizioni patologiche, quali malat-
tie infiammatorie a decorso cronico, atopia, insufficienza renale cronica ed
alcuni tipi di tumore. È pertanto molto importante tenere conto del tipo e
della quantità delle fonti lipidiche che si impiegano nella formulazione del-
le diete di cani e gatti, al fine di assicurare la giusta quantità ed il corretto
rapporto di acidi grassi essenziali nell’alimento.
Introduction
Over the past 30 years, many stud-
ies have been conducted to investi-
gate the metabolism of polyunsatu-
rated fatty acids (PUFA) in hu-
mans and animals. Today, it is well
known that both omega-3 and
omega-6 fatty acids are essential in
mammalians for normal growth
and prevention of several diseases,
such as cardiovascular diseases, dia-
betes, hypertension, chronic in-
flammatory and autoimmune dis-
orders, and cancer.
The recommendations to increase
omega-6 fatty acids uptake to re-
duce plasma concentration of cho-
lesterol in humans have strongly
influenced seed oil production and
feeding techniques of farm animals.
The large use of grains and oils rich
in omega-6 fatty acids as feedstuffs
for farm animals has led to the pro-
duction of meat and eggs rich in
omega-6 and poor in omega-3 fatty
acids. Furthermore, modern aqua-
culture produces fish containing
less omega-3 fatty acids than wild
fish (1). As a consequence, diets for
humans as well as homemade diets
for dogs and cats are very likely to
be high in omega-6 and low in
omega-3 fatty acids.
The metabolism of omega-3 and
omega-6 essential fatty acids
The omega-3 and omega-6 fami-
lies consist of several fatty acids de-
rived from two precursors, linoleic
acid (LA, C18:2 n-6) and α-
linolenic acid (LNA, C18:3 n-3).
These two fatty acids can not be
synthesized by animals and must be
obtained from the diet. Once in-
gested, LA and LNA undergo the
action of two enzymic systems,
known as desaturase and elongase,
and are metabolised in other acids
of the same series. The desaturases
act by replacing a saturated bond
with a double one, the elongases
exert their action adding carbon
atoms to the acid in order to extend
the chain. The metabolic pathway
of the omega-3 and omega-6 fatty
acids is shown in figure 1.
Omega-3 and omega-6 fatty acids
compete for the same desaturase
enzymes (2). As a result, the pro-
portions of omega-6 and omega-3
2
VOLUME 6
Figure 1 - Metabolic pathway of the omega-3 and omega-6 fatty acids
AA = arachidonic acid; EPA = eicosapentaenoic acid; DHA = docosa-
hexaenoic acid
fatty acids that are available to
these enzymes directly affect the
quantity and proportions of arachi-
donic acid (AA, C20:4 n-6), eicos-
apentaenoic (EPA, C20:5 n-3) and
docosahexaenoic acid (DHA,
C22:6 n-3) that are formed.
Like other obligate carnivores, cats
show only little d-6 desaturase ac-
tivity and require foods of animal
origin as a source of AA, EPA and
DHA (3). Conversely, dogs are able
to convert LA and LNA to the
long-chain PUFA by desaturase
and elongase systems (4, 5).
The biological role of omega-3 and
omega-6 fatty acids
Long chain PUFA can have both a
functional and a structural role.
Arachidonic acid is found in fairly
high proportions in the membranes
of most cells, where it is bound as a
component of phospholipids. Upon
cellular stimulation AA is released
and becomes the substrate for the
synthesis of eicosanoids. Eicosa-
noids are polyunsaturated metabo-
lites of fatty acids which include
prostaglandins, thromboxanes,
leukotrienes, and hydroxylated
eicosatetraenoic acids (lipoxins).
DHA is an essential component of
cell membranes. DHA is particu-
larly present in the phospholipids
of retina, cerebral synaptosomes,
and sodium intra-membranous
channels (6). DHA seems to play a
very important role in:
1) brain development and growth
2) reproductive apparatus develop-
ment and growth
3) retinal tissue development and
growth
EPA is mainly a precursor of
eicosanoids. When the diet is rich
in omega-6 and poor in omega-3
fatty acids, eicosanoids are mainly
produced from AA, but when ani-
mals ingest enough omega-3 fatty
acids, EPA and DHA partially re-
place the omega-6 fatty acids (es-
pecially AA) in cell membranes.
When the cell is injured, EPA and
AA are released from the mem-
brane by a phospholipase and
metabolised to eicosanoids by two
main enzymatic systems, ciclooxi-
genase and lipoxygenase. The
metabolic pathways for the produc-
tion of eicosanoids from AA and
EPA are shown in figure 2.
Eicosanoids that are derived from
AA are pro-inflammatory and pro-
aggregatory, and act as potent me-
diators of inflammation in type I
hypersensitivity reactions. Eicosa-
noids from EPA are less inflamma-
tory, vasodilatory, anti-aggregatory,
and prevent cardiac arrhythmia (6).
These actions resist those produced
by the eicosanoids from AA. The
main actions of EPA and AA are
summarized in table 1.
Dihomo-γ-linolenic acid (DGLA,
C20:3 n-6) is produced through
elongation from γ-linolenic acid
(GLA, C18:3 n-6). The eicosa-
noids (group 1 prostaglandins and
group 3 leukotrienes) that derive
from DGLA suppress the synthesis
of tumor necrosis factor-a which is
a strong proinflammatory cytokine.
Dietary sources of PUFA
Omega-6 fatty acids are widely dis-
tributed in food of vegetable and
animal origin. Most oils consumed
in the Western countries (particu-
larly corn, peanut, and sunflower
oil) are very rich in LA and contain
only little LNA. Among vegetable
oils, flaxseed oil is the one showing
the highest content in LNA; signif-
icant amounts of LNA are present
also in rapeseed and soybean oil,
and in walnuts. A major source of
EPA and DHA is oily fish, such as
sardine, salmon, mackerel, and
fresh tuna. The fatty acid composi-
tion of some foodstuffs is reported
in table 2.
Deficiency of PUFA in dogs and
cats
Deficiencies of PUFA are not very
common in dogs and cats. Com-
mercial diets usually contain ade-
quate PUFA; nevertheless, products
that contain significant amounts of
PUFA must be protected from oxi-
dation with the inclusion of natural
or synthetic antioxidants and
avoiding all the factors that may
activate lipids oxidation during
production and storage, such as
light, high temperature, and hu-
midity. Deficiencies of PUFA may
PROGRESS IN NUTRITION 2/2004
3
occur when animals are fed for a
prolonged time inadequate home-
made diets or diets that have un-
dergone oxidation of lipids.
A PUFA deficiency in dogs is char-
acterized by dull dry hair, hair loss,
and skin lesions (7). Hansen and
Wiese (8) reported cases of external
otitis in PUFA-deficient dogs.
Because of their inability to convert
LA into AA (as well as LNA into
EPA and DHA), cats are more
likely to develop a PUFA deficien-
cy.When cats are fed a diet lacking
LA, they show signs of deficiency,
such as poor growth, skin lesions,
increased loss of water through the
skin, reduced platelet aggregation,
reproductive failure, and fatty liver.
These signs of deficiency may be
prevented by including LA into the
diet. Nevertheless, cats fed diets
containing adequate LA but lack-
ing AA showed reproductive failure
and impaired platelet aggregation
(9-11). Interestingly, male cats fed
LA-adequate AA-deficient diets
show normal reproduction func-
tions. This finding suggests that
some conversion of LA into AA
may take place (11). The existence
of some δ-6 desaturase activity in
cats was later confirmed by
Pawlosky et al. (12).
In rats, δ-6 desaturase activity in
the liver decreases at a rate propor-
4
VOLUME 6
Figure 2 - Metabolic pathways for the production of eicosanoids from AA and EPA
AA = arachidonic acid; EPA = eicosapentaenoic acid; DGLA = Dihomo-g-linolenic acid
tional to the animal age (13). Even
if there are no specific studies in
the dog, it seems reasonable that
also in old dogs the liver δ-6 desat-
urase activity may be lower and, as
a consequence, the conversion of
LA and LNA to their derivatives
may be decreased. Therefore,
adding a source of AA, EPA and
DHA to the diet of old dogs may
be helpful in preventing a deficien-
cy of these PUFA.
Excessive intake of PUFA in dogs
and cats
Cases of vitamin E deficiency in
cats receiving diets very high in
PUFA have been reported. Diets
with a very high fish content may
cause steatitis (“yellow fat disease”)
in cats if they are deficient in vita-
min E (14, 15). Momoi et al. (16)
observed that healthy cats receiving
a raw fish diet had a significant in-
crease of plasma lipid peroxide lev-
el. When a cat diet is very rich in
PUFA, the NRC (17) suggests a 3-
4 fold increase of vitamin E inclu-
sion in the food. Feeding dogs with
a diet with a very low omega-
6/omega-3 fatty acid ratio (1.6:1)
reduced plasma concentration of α-
tocopherol and increased lipid per-
oxidation (18).
The role of PUFA in the
development of the nervous system
of dogs and cats
The mammalian brain is very rich
in PUFA, especially DHA and AA
(19). In the retina, the rod outer
segment membranes of the pho-
toreceptors are very rich in DHA
(20). Essential fatty acid deficiency
during early brain development
may produce permanent and dele-
terious effects (21). Therefore, ade-
quate PUFA dietary levels in the
mother are very important both
during foetal and early postnatal
period. Ward et al (20) observed
that dietary supplementation with
different levels of DHA and/or AA
in neonatal rats increased deposi-
tion of PUFA in the brain but also
affected tissue levels of the other
acid.
In dogs, the retinal tissue is able to
synthesize DHA from docosapen-
taenoic acid (DPA, C22:5 n-3)
which can be obtained from LNA
(4). However, because the quantity
of LNA that is needed to optimise
neural tissue development is not
known, feeding bitches and puppies
with a source of dietary DHA is
the best approach to provide the
puppies with this nutrient.
In cats, brain DHA levels increase
during the last weeks of pregnancy
PROGRESS IN NUTRITION 2/2004
5
Arachidonic acid Effect EPA Effect
PGE2Platelet aggregation PGI3Platelet aggregation,
vasodilation
LTB4Inflammation LT B 5Inflammation
TXA2Platelet aggregation, TXA3Platelet aggregation
vasoconstriction vasoconstriction
TNF-α↑Inflammation IL-2b
IL-1β↑Inflammation Nitric Oxide Vasodilation
PAF Platelet aggregation
PAF = Platelet activating factor
Table 1 - Main actions of arachidonic and eicosapentaenoic acid (EPA)
and keep increasing during early
life. Sources of DHA and AA must
be present in the diet of the queen
to assure the correct development
of brain and retina of the kittens
(22).
The influence of PUFA on the
immune system of dogs and cats
As previously mentioned, dietary
lipids may modulate the immune
system influencing eicosanoids pro-
duction. Kearns et al. (23) showed
that, despite the antiinflammatory
properties of omega-3 PUFA, re-
ducing the omega-6/omega-3 fatty
acid ratio in the diet of dogs to 5:1
did not negatively affect the im-
mune function of old animals and
had some positive effect on the im-
mune system of young animals.
Feeding dogs with a diet rich in fish
oil reduced the production of
leukotriene B4,a strong proinflam-
matory eicosanoid derived from
AA, by neutrophiles (24, 25). In
another study (26), when dogs were
fed a diet with an omega-6/omega-
3 fatty acid ratio of 1.4:1, CD4+ T
lymphocyte count after vaccination
was lower than in control animals,
showing that a very low omega-
6/omega-3 fatty acid ratio reduced
immune response to vaccination. A
diet with an omega-6/omega-3 fat-
ty acid ratio of 1.4:1 reduced cell-
mediated immune response and
PGE2production in aged dogs (18).
6
VOLUME 6
Foodstuff Total Saturated Monouns. Polyunsaturated FA
FatFAFAC18:2 C18:3 C20:4 C20:5 C22:6 TOT
Beef, rib 6.1 2.03 1.99 0.57 0.11 0.16 0.14 0.07 1.21
Chicken, breast 0.9 0.29 0.23 0.11 0 0.07 0 0.02 0.25
Lamb, leg 2.5 1.01 0.86 0.24 0.01 0.09 0 0 0.35
Pork, loin 7.0 2.23 2.38 1.68 0 0.03 0 0 1.82
Mackerel 11.1 2.61 4.13 0.16 0.15 0.16 0.73 1.26 2.46
Salmon, fresh 12.0 2.97 4.60 0.15 0.09 0.05 0.89 1.19 3.05
Sardine 15.4 4.71 2.89 0.18 0.69 1.05 1.73 2.35 6.29
Tuna, fresh 8.1 3.35 1.51 0.15 0.09 tr. 0.80 2.15 3.20
Egg, whole 8.7 3.17 2.58 1.06 0.04 0.16 0 0 1.26
Butter 83.4 48.78 23.72 1.57 1.18 0002.75
Margarine 84.0 26.43 36.78 16.62 1.02 0 0 0 17.64
Corn oil 99.9 14.96 30.66 49.83 0.60 0 0 0 50.43
Flaxseed oil 99.9 9.40 20.20 12.70 53.30 0 0 0 66.00
Olive oil 99.9 16.16 74.45 7.85 0.99 0008.84
Peanut oil 99.9 19.39 52.52 27.87 000027.87
Rapeseed oil 99.9 6.31 61.52 20.54 9.08 0 0 0 29.62
Soybean oil 99.9 14.02 22.76 51.36 7.60 0 0 0 58.96
Sunflower oil 99.9 11.24 33.37 49.89 0.33 0 0 0 50.22
Walnuts 68.1 5.57 9.54 34.02 6.64 0 0 0 40.66
*Data from Marletta L, Carnovale E: Composizione degli alimenti. Aggiornamento 2000. Istituto Nazionale di Ricer-
ca per gli Alimenti e la Nutrizione. 2000. CDROM.
FA = fatty acids
Table 2 - Fatty acid composition of some foodstuffs (g per 100 g of edible portion)*
Because of the antiinflammatory
properties of the omega-3 PUFA,
many studies have been conducted
in animals and humans to investi-
gate the influence of dietary PUFA
on chronic diseases, such as arthro-
sis, dermatitis, and autoimmune
diseases.
In human patients with rheuma-
toid arthritis, clinical improvement
is achieved with the consumption
of fish oil (27). Simopoulos (28)
has reviewed the beneficial effects
of omega-3 PUFA in human pa-
tients with inflammatory and au-
toimmune diseases.
In dogs with experimental and in-
fectious arthritis, leukotriene B4is
increased in synovial fluid (29, 30),
as it is in human patients with
rheumatoid arthritis (31). The re-
duction of the omega-6/omega-3
acid ratio in the diet of dogs with
osteoarthrosis of the elbow joint did
not reduce lameness during a 12
week study (32). At the present
time, considering the lack of litera-
ture, it is not possible to assess the
effects of dietary omega-3 PUFA on
chronic arthritis of dogs and cats.
In dogs, omega-3 PUFA have been
successfully used to treat a claw
disorder called symmetrical lupoid
onychodystrophy, usually charac-
terised by pain and lameness (33,
34).
The role of PUFA in the treatment
of allergic dermatitis in dogs and
cats will be discussed in the next
paragraph.
The role of PUFA in the treatment
of atopy in dogs and cats
Many studies have investigated the
efficacy of PUFA in the manage-
ment of canine and feline atopy (al-
lergic inhalant dermatitis). It has
been estimated that 10-15% of the
canine population is affected by
atopy (35). Other types of allergies
that may be responsible for an al-
lergic dermatitis are flea bites and
food ingredients. The main clinical
sign of allergic dermatitis is pruri-
tus with secondary skin lesions
mainly resulting from self-trauma.
Depending on the presence of the
responsible allergens, pruritus may
or may not be seasonal. Otitis ex-
terna is noted in about 55% of the
dogs with atopic dermatitis (36).
Scott et al. (37) observed that a
commercial diet with an omega-
6/omega-3 fatty acid ratio of 5.5:1
reduced pruritus in almost 50% of
the atopic dogs used for the trial.
The favourable response was ob-
served after 7 to 21 days on the di-
et, and was lost 3 to 14 days after
the diet was withdrawn. During
another study with atopic dogs,
Harvey (38) observed that skin
condition was improved in animals
receiving a combination of fish oil
(rich in EPA and DHA) and bor-
age seed oil (rich in GLA) com-
pared to the control animals receiv-
ing olive oil as a placebo. During
another study, skin condition im-
provement was observed in 19 of
26 atopic dogs receiving a mixture
of fish oil and evening primrose oil
(also rich in GLA; 39). Another
source of GLA is blackcurrant seed
oil. When fed to atopic dogs,
blackcurrant seed oil reduced pruri-
tus, erythema and skin lesions (40).
Conversely, other researchers did
not notice any significant benefits
from feeding fish oil and evening
primrose oil to atopic dogs (41,
42). In another trial (43), changing
the dose of omega-3 PUFA and
the omega-6/omega-3 ratio did not
produce any benefit on clinical
signs in dogs with pruritus.
In cats with crusting dermatosis,
Harvey (44) observed that a mix-
ture of evening primrose oil and
fish oil was more effective than fish
oil alone in improving skin condi-
tion. During a precedent study
(45), six of eight cats with pruritus
showed some benefit from dietary
supplementation with PUFA.
Feeding an omega-3 fatty acid sup-
plement to non-pruritic cats with
miliary dermatitis lead to the com-
plete disappearance of clinical signs
in three animals of five (46). Con-
versely, in another study, feeding
primrose oil to 15 pruritic cats did
not improve their skin condition
(47). When used together with an
antihistamine, an omega-3/omega-
6 fatty acid supplement was effec-
tive in reducing pruritus in 6 cats of
11 (48). Interestingly, no benefit
was observed when the antihista-
mine or the fatty acid supplement
PROGRESS IN NUTRITION 2/2004
7
were used alone, suggesting a syn-
ergistic action of the two antiin-
flammatory agents tested.
The lack of clear benefits from
feeding PUFA to dogs and cats
with dermatitis and the sometimes
controversial results obtained may
be due to different causes, such as
inadequate duration of treatment,
lack of a control diet, different
composition of diets and supple-
ments used in the experiments, dif-
ferent doses of PUFA fed to the
animals, and different etiology of
disease.
Cardiovascular effects of PUFA in
dogs
The beneficial effects of omega-3
fatty acids on coronary heart dis-
ease have been shown in hundreds
of experiments in animals and hu-
mans (49). Dietary omega-3 fatty
acids prevent heart disease through
several actions, such as prevention
of arrhythmias, production of
prostaglandins and leukotrienes
with antiinflammatory properties
and inhibition of the synthesis of
cytokines and mitogens that aug-
ment inflammation, stimulation of
nitric oxide release, antithrombotic
properties, reduction of plasmatic
triacylglycerols and VLDL, and in-
hibition of atherosclerosis (50).
Despite the fact that atherosclerosis
is not a major clinical problem in
dogs and cats, it is known that sled
dogs like trained human athletes
may develop pathological alter-
ations of the heart conduction sys-
tem (fibrosis and fat infiltration)
that can eventually lead to sudden
death (51). Billman et al. (52, 53)
showed that omega-3 PUFA have
antiarrhythmic effects also in dogs
and can prevent sudden cardiac
death. Kang and Leaf (54) ob-
served that omega-3 PUFA stabi-
lize electrically every myocyte in
the heart of dogs by increasing by
approximately 50% the electrical
stimulus required to elicit an action
potential and prolonging the rela-
tive refractory time by approxi-
mately 150%.
Freeman et al. (55) showed that
fish oil supplementation can im-
prove the health status of dogs with
heart failure, reducing Interleukin-
1β(IL1) production and improving
the cachexia that is often associated
with heart failure. IL1 is correlated
with higher mortality rates and this
may be the consequence of the
negative inotropic effect of IL1 or
of the fact that IL1 increases skele-
tal muscle protein turnover and re-
duces cardiac myocyte protein syn-
thesis (56).
The role of PUFA in the treatment
of chronic renal disease in dogs and
cats
Despite the fact that renal disease
is a very common cause of death in
dogs and cats, the causes of renal
disease and its progression are only
poorly understood. In dogs and
cats with renal insufficiency,
glomerular hypertension and hy-
pertrophy are observed (57, 58).
These findings are supposed to
represent the adaptive renal re-
sponse to the injury. Frequently, re-
nal failure with glomerular hyper-
tension is associated with elevation
of systemic arterial pressure of dogs
and cats (59, 60). In dogs with re-
nal failure, preglomerular vessels
are dilated and even transient ele-
vations of systemic pressure are
transmitted to the susceptible
glomerular capillary bed causing
further progression of the disease
(61).
Intrarenal hemodynamics are influ-
enced by vasoactive renal eicosa-
noids, such as Prostaglandin E2and
I2and Thromboxane A2(62, 63),
both deriving from AA. While
PGE2and PGI2are powerful va-
sodilators and help maintain renal
blood flow and glomerular filtra-
tion, TXA2reduces renal blood
flow and glomerular filtration and
induces aggregation of platelets
(64). Intrarenal platelet aggregation
may lead to proteinuria due to
higher capillary permeability and to
intraglomerular coagulation with
subsequent fibrosis and sclerosis
(65). Conversely, TXA3,which is
derived from EPA, does not cause
platelet aggregation (66).
Brown et al. (67) fed dogs with re-
nal insufficiency different sources
of fat. Feeding the animals with
8
VOLUME 6
safflower oil (rich in omega-6 fatty
acids) enhanced renal injury while
feeding fish oil prevented deterio-
ration of renal function. Dietary
supplementation with beef tallow
(a source of saturated fatty acids)
also produced a progressive decre-
ment of renal function but the rate
of function decline was slower than
in animals receiving safflower oil.
During another study (68), dogs
with early renal insufficiency were
fed safflower oil, fish oil or beef tal-
low. Compared to feeding beef tal-
low, feeding fish oil decreased
serum cholesterol concentration
and PGE2and TXA2excretion,
while dietary supplementation with
safflower oil increased eicosanoids
excretion, glomerular capillary
pressure and glomerular enlarge-
ment.
The role of PUFA in the
prevention and treatment of
neoplastic disorders in dogs and
cats
In humans, there is evidence that
omega-3 fatty acids may have some
beneficial effect on some neoplastic
diseases, such as breast, colorectal,
and prostatic cancer, preventing de-
velopment and growth of tumors
and reducing the incidence of
metastatic disease (69-72).
Cachexia is a very common conse-
quence of malignancy and it is
caused by a number of derange-
ments in carbohydrate, lipid and
protein metabolism that are ob-
served in humans (73, 74) as well
as in dogs (75, 76). Since TNF and
interleukin-6 are supposed to play a
role in the pathogenesis of cancer
cachexia (77), feeding fish oil to
cancer patients may reduce the pro-
duction of these eicosanoids and
consequently the incidence of
cachexia (78, 79).
In dogs with lymphoma, dietary
omega-3 fatty acids significantly
increased disease free interval and
survival time (80).
Conclusions
There is evidence from the litera-
ture that the omega-6/omega-3
fatty acid ratio of the diet influ-
ences growth and health status of
dogs and cats. Essential fatty acids
are very important for the develop-
ment of the nervous system and an
optimal dietary omega-6/omega-3
fatty acid ratio (about 6 to 1) re-
duces the incidence of some dis-
eases, such as cancer and sudden
cardiac death. Furthermore, the use
of fatty acid supplements has
proved to be beneficial in the treat-
ment of several pathogenic condi-
tions, such as chronic inflammatory
diseases, atopy, chronic renal dis-
ease, and some types of cancer.
Therefore, particular attention
should be paid to the type and
quantity of fat sources that are used
when diets for dogs and cats are
formulated, in order to assure the
optimal amount and balance of
omega-3 and omega-6 fatty acids
in the food.
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