Fish Oil Dosing in Pet Diets and Supplements

Commercial pet food production uses an array of animal and vegetable fats and oils to supply energy and, when applied topically during manufacturing, as palatability enhancers.¹ Fats are composed of fatty acids with carbon chains of various lengths and are described as “unsaturated” or “saturated” (no double bonds in the carbon chain). Fatty acids with the first double bond occurring between carbons 3 and 4 from the methyl group comprise the omega-3 family, whereas the omega-6 family has the first double bond between carbons 6 and 7. Fatty acids from both families that are not synthesized by the body are considered essential fatty acids (EFAs) for dogs, cats, and other mammals.

Omega-6 EFAs include linoleic and arachidonic acid. The omega-3 EFAs are α-linolenic acid, eicosapentanoic acid (EPA), and docosahexaenoic acid (DHA). Linoleic acid is known to be a dietary requirement for adult dogs and cats; adult cats also require dietary arachidonic acid. DHA is required for growing puppies and kittens, and there is growing consensus that it, along with EPA, should be considered an essential nutrient for all life stages of dogs and cats, but the optimal amount and form to be included in pet diets are still unknown.

Animal fats used in pet diets are high in omega-6 fatty acids, whereas fish oils, dried algae, marine microalgae, fish meals, or whole fish are used specifically as sources of omega-3 fatty acids. Fish oil supplements with concentrated amounts of EPA and DHA should therefore be considered as providing a “therapeutic or even pharmacological effect,” rather than simply supplying an essential nutrient in pet foods.²

Essential Fatty Acids in Pet Foods

Recommended Levels

Studies in growing puppies have identified DHA’s role in developing neurologic tissues with improved retinal development and cognitive function testing.³ The Association of American Feed Control Officials (AAFCO) uses these types of studies, as well as published data by the National Research Council (NRC), to recommend nutrient levels for pet food manufacturers. The NRC states adequate intake and recommended allowances of EPA and DHA for growth as well as adult maintenance of dogs and cats.⁴

Currently, AAFCO has no minimum EPA or DHA requirements for adult canine or feline maintenance diets. However, AAFCO does recommend that diets for canine growth and reproduction contain a combination of EPA and DHA at 0.05% dry matter basis or 10 mg/100 kcal, and that feline growth and reproduction diets contain 0.012% EPA and DHA or 3 mg/100 kcal.⁵ AAFCO recommends a safe upper limit of omega-6:omega-3 fatty acids at 30:1 for dog foods, but as a ratio of the total grams of linoleic and arachidonic acid (omega-6s) to total grams of α-linolenic acid, EPA, and DHA (omega-3s). The NRC’s safe upper limit for dogs, and specifically for total EPA and DHA content, is 280 mg/100 kcal.

Functions

Dietary fats in pet diets supply 2.25 times the metabolizable energy of protein and carbohydrates. EFAs also have a structural role in the bilipid membranes of cells. Here, they are used by the lipoxygenase and cyclooxygenase enzyme systems to form prostaglandins and leukotrienes, which mediate inflammation. Prostaglandins and leukotrienes derived from arachidonic acid (omega-6) are proinflammatory, whereas those derived from EPA and DHA (omega-3) result in a reduced inflammatory response with decreased platelet aggregation and immunologic stimulation. The resolution of inflammation is an active process involving resolvins and protectins derived specifically from EPA and DHA.⁶ These endogenous mediators form in the resolution phase of the inflammatory response and serve to stop inflammation and to reduce leukocyte-mediated tissue injury.

Supplementation EPA and DHA

As the market for human and pet supplements continues to grow, clients are increasingly aware of the numerous reported health benefits of cold-water fish oil supplements containing EPA and DHA. Some of the benefits of these supplements may be explained by the decrease and resolution of inflammatory responses by EPA- and DHA-derived resolvins and protectins.

Therapeutic Uses in Dogs

The “anti-inflammatory effects” of EPA and DHA in dogs with various diseases—including hyperlipidemia, kidney disease, cardiovascular disorders, osteoarthritis, atopy, and inflammatory bowel disease—have been evaluated.⁷ In dogs, recommended doses of EPA and DHA supplements for therapeutic purposes range from 50 to 220 mg/kg body weight. The highest dose is recommended for osteoarthritis. These therapeutic doses are based on adding the milligrams of EPA and DHA per supplement capsule or milliliters of liquid, which is meant to be the “active ingredient” in many common pet fish oil supplements (TABLE 1).^7-10

Pet supplements for joint, skin, and gastrointestinal problems are increasingly popular, and supplements containing EPA and DHA are common. As the EPA and DHA in fish oil supplements are being used for their pharmacologic effects, their potential adverse effects should be considered. Supplement–drug interactions, altered platelet function, gastrointestinal disturbances, detrimental effects on wound healing, nutrient excess/weight gain, altered immune function, and effects on insulin sensitivity have the potential to make fish oil supplementation problematic.¹¹ In a study of 31 dogs with reticulocytosis in the absence of anemia (RAA), more than 90% of dogs regularly consumed omega-3 EFAs and/or glucosamine, either in the diet or as a separate supplement. Furthermore, RAA dogs were often administered nonsteroidal anti-inflammatory drugs (NSAIDs). The authors speculated on the potential role of NSAIDs in gastric ulceration and enhanced chronic blood loss with concurrent omega-3s and/or glucosamine, which can interfere with normal platelet function, as being a potential cause of RAA in this population of dogs.^12-17

Cats and Omega-3s

Data on omega-3 therapeutic supplementation in cats are scarce. One retrospective study of survival of cats with chronic kidney disease compared cats consuming a maintenance diet with those eating 1 of 7 commercially available renal diets. The renal diet with the highest EPA content (200 mg/100 kcal) was associated with the longest survival.¹⁸ Another randomized, controlled, blinded prospective study that evaluated 40 client-owned cats with osteoarthritis fed a feline diet containing 188 mg EPA + DHA/100 kcal and supplemented with green-lipped mussel extract (a source of glucosamine/chondroitin sulfate) noted improved objective measures of mobility.¹⁹ Using the milligrams of omega-3s per kilocalorie in these studies would suggest a dose of approximately 112 or 120 mg of combined EPA + DHA per kilogram of body weight for cats with chronic kidney disease or osteoarthritis, respectively.

Combining EPA And DHA in Pet Foods and Supplements

Practitioners should be aware of the benefits and potential for adverse events when using fish oil supplementation in conjunction with diets containing EPA and DHA. Manufacturers should provide information to allow practitioners to easily assess the milligrams of EPA and DHA in pet supplements, over-the-counter diets, and veterinary therapeutic diets (VTDs).

EPA and DHA Content of Commercial Diets

For this article, the authors contacted 5 pet food companies by email to obtain the current total omega-6, omega-3, EPA, and DHA content of their bestselling canine VTDs (joint, novel protein, hydrolysate, renal, gastrointestinal, and weight loss, if available) and 3 top-selling over-the-counter diets. Two companies complied, 2 referred to their current product guides, and 1 did not provide guidance. Only 2 companies provided specifics on diet sales; therefore, fatty acid analysis and comparisons were restricted to selected VTDs. TABLE 2 summarizes the information obtained. While the amount of EPA and DHA varies by category of diet and company, in general, the highest amounts are in the joint diets, ranging from 160 mg to 340 mg/100 kcal. Noteworthy among the other diets are Purina’s (purina.com) novel protein (240 mg/100 kcal), Blue Buffalo’s (bluebuffalo.com) renal (190 mg/100 kcal), and Rayne’s (raynenutrition.com) weight loss (160 mg/100 kcal) diets. TABLE 3 provides therapeutic doses of EPA + DHA for specific disease conditions.

Example: Diet Plus Supplementation

Using the data in TABLE 2, the authors calculated the total daily intake of EPA and DHA for a 20 kg dog consuming its daily energy requirement of 927 kcal of the VTD in each category that contained the highest amounts of EPA + DHA/100 kcal (TABLE 4). Next, the daily intake of EPA and DHA was compared to the recommended therapeutic dose of EPA + DHA for the corresponding disease state to determine the percentage of the therapeutic dose that would be met by VTD intake. In most cases, a 20 kg dog consuming a veterinary joint, novel, hydrolyzed, renal, or weight loss therapeutic diet containing high levels of EPA and DHA would likely obtain the recommended therapeutic dose from the diet alone; therefore, additional omega-3 supplementation may be unnecessary or, at least, should be carefully assessed.

Because the canine joint VTDs assessed for this article contained the highest amounts of EPA and DHA, it may be prudent to avoid omega-3 supplements or at least assess their dosing for safety and economics when recommending a canine joint VTD. In the TABLE 4 example of the 20 kg dog consuming 3152 mg of EPA + DHA per day in its joint diet, the addition of a daily capsule of a typical omega-3 pet supplement containing 500 mg of EPA +DHA (TABLE 1) would result in a total daily intake of 3652 mg. This amount exceeds the NRC safe upper limit of 3499 mg of EPA + DHA for this patient (TABLE 3).

Conclusion

Based on the data provided in TABLE 2, when considering the use of a canine novel, hydrolysate, renal, gastrointestinal, or weight loss VTD, the authors recommend determining total EPA and DHA intake provided by the diet to ensure safe and economic omega-3 supplementation. This may require contacting the manufacturer. Question clients about current diet and all supplements that they may be feeding. In summary, EPA and DHA may be beneficial in disease states, but because of their pharmacologic effects, care should be used when recommending EPA and DHA–containing VTDs and pet supplements concurrently.