Dr Liesel van der Merwe, BVSc MMedVet(Med)Small Animals
University Of Pretoria , Department of Companion animal Clinical Studies
Fat is a source of energy, fat soluble vitamins and essential fatty acids. The type of fatty acids can have significant effects on immune function and production of inflammatory mediators. Polyunstaurated fatty acids (PUFAs’) can be divided in omega-3 and omega-6.
Most canine diets contain mainly omega-6 (LA, γ-LA (GLA) and AA) fatty acids. Omega-3 fatty acids (α-LA, EPA and DHA) have a first double bond at the 3C instead of the 6C region, hence the names, and this confers a very different structure and function to the molecule. Structural and metabolic differences exist between omega-3 and omega-6 fatty acids and they do not metabolically interconvert. Blood plasma levels usually contain a low level of omega-3 which can be increased by diet or supplementation.
• LA (linoleic acid) is found in most vegetable oils it represents more than 70% of the fatty acids in evening primrose oil and more than 50% in sunflower oil, wheat, corn and soy.
• ALA (α-linoleic acid) is found in green vegetable, grasses fruits and plankton, and is found in concentrated forms in the oils from soy and flax.
• GLA (γ-linoleic acid) – safflower oil, hemp oil and borage oil.
• EPA (eicosapentaenoic acid) and DHA (docosapentaenoic acid) are long chain omega-3 fatty acids are found in the oils of fish from cold waters. Shorter chain omega-3 fatty acids are found in linseed oil.
PUFAs’ fulfil four main functions:
• Incorporation into the cell membrane giving flexibility and permeability
• Production of eicosanoids (less inflammatory ones)
• Maintenance of skin barrier permeability
• Cholesterol metabolism and transport
The omega-3 fatty acids, EPA and DHA, modulate eicosanoid synthesis as they compete with arachidonic acid for the cyclo-oxygenase and 5-lipo-oxygenase enzymes involved in the arachidonic acid cascade leading to the production of less inflammatory 3-series eicosanoids. Oxidative stress and inflammation can thus be altered by dietary factors in various species.
Dogs easily convert linoleic acid (LA) into arachidonic acid (AA) and related pro-inflammatory eicosanoids. The conversion of α-LA to EPA and less inflammatory eicosanoids occurs at a lower rate. Conversion of α-LA to DHA is even lower. The metabolism of LA and α-LA depends on the same enzyme systems and is thus competitive. Thus to avoid excessive omega-6 (LA) metabolites, inclusion of omega-3 fatty acids (α-LA) to balance dietary LA is recommended.
Omega 3 fatty acids are probably “conditionally essential” nutrients given the low conversion rates of α-LA to EPA and DHA. Thus long chain omega-3 fatty acids are generally conditionally essential for growth, development metabolic balance and possibly healthy ageing.
Feral dogs are likely to obtain both α-LA and DHA from the liver and nervous tissues of small mammalian prey and birds which more readily convert dietary omega -3 precursors in plants to the longer chain omega-3 fatty acids.
DHA is well conserved in tissues and in adult dogs at maintenance may not require long chain fatty acids as the small amounts converted from α-LA may be sufficient, however inclusion in the diet is still recommended due to individual variations in synthesis. DHA is present in large amounts in the brain and retina and it is essential for the development of the nervous system and visual acuity.
Role of DHA in dogs
Cognition and healthy ageing
Antioxidant enriched diets containing a small amount of DHA have been found to be potentially beneficial in dogs. In addition a few reports have found associations between DHA and seizure treatment and possible aggression in dogs.
Development of puppies
Puppies appear to synthesize DHA from α-LA in early life when still suckling, but lose this ability after weaning. Thus when the demand for DHA is especially high they can meet this demand. Puppies with proper omega -3 supplementation before and after weaning, had better visual and cognitive function than those without, which were however still considered normal.
Skin conditions: Canine Atopic Dermatitis (CAD)
Omega-3 fatty acids favour the production of less inflammatory eicosanoids as well as stabilise the epidermal lipid barrier. PUFAs’ are insufficient as a sole therapy for canine atopic dermatitis. Lower omega 6:3 ratios are more effective. A recent publication used a supplement with a ratio of omega -3:6 of 1:3.75 to evaluate its cyclosporine sparing effects and found that the dose of Atopica ® could decrease from 4.1 mg to 2.6mg/kg and the median pruritis score decreased significantly in the patients receiving supplementation. ( Müller MR et al Vet Journal 2016 (210) 77-81)
Management of primary hyperlipidaemia is achieved by ultra-low fat diets with or without the administration of lipid lowering drugs such as omega 3 fatty acids, fibrates, niacins and statins. Synthesis of triglycerides and VLDL in the liver is decreased by omega-3 acids.
Congestive heart failure
Omega-3 fatty acids are known to decrease the production of inflammatory cytokines, TNF and IL-1, which are elevated in CHF. Fish oil supplementation reduces cachexia and increase appetite is some dogs with CHF.
Arachidonic acid (AA) forms the pro-inflammatory series -2 eicosanoids, whereas EPA is converted to the less inflammatory series-3 eicosanoids. By altering the amounts of omega-3 and omega- 6 in the diets production of less inflammatory eicosanoids is favoured. GLA is an omega-6 fatty acid which also converts into less inflammatory eicosanoids, however omega-3 fatty acids seem to provide superior results.
EPA and DHA can have a profoundly suppressing effect on cancer cachexia.
Remnant kidney studies in dogs have reported that long chain omega- 3-fatty acid supplementation reduces inflammation, lowers systemic arterial pressures, alters plasma lipid concentrations, and preserves renal function.
LA – linoleic acid
ALA / α-LA – alpha linoleic acid
GLA / γ-LA – gamma linoleic acid
EPA – eicosapentaenoic acid
DHA – docosapentaenoic acid
AA – arachidonic acid