Krill – The Other Fish Oil

There is currently quite a craze in the dog world regarding omega-3 fatty acids. I reviewed this important family of fatty acids and their role in canine health in a recent blog (see Facts about Flax).

In short: As a recap, it is probably beneficial to increase the proportion of omega-3 fatty acids in our dogs’ diets. This is best accomplished by feeding foods with a reduced proportion of omega-6 fatty acids (NOT eliminating them altogether…..remember, linoleic acid, the parent omega-6 fatty acid is an essential nutrient for dogs), and containing an increased proportion of omega-3 fatty acids. Because foods produced with our current agricultural systems result in high levels of dietary omega-6 fatty acids, focus generally centers on increasing the omega-3 fatty acid family.

Not Flax: We also know that adult dogs are inefficient converters of alpha-linolenic acid (the parent omega-3 fatty acid) to the long-chain omega-3 fatty acids (EPA and DHA) that are most associated with health benefits. Therefore, flax is not considered to be an enriched source of the long-chain omega-3 fatty acids for dogs. Rather, certain types of fish oils (and microalgae) are identified as good sources.

Which brings us to krill.

Why Krill? The long-chain omega-3 fatty acids can be supplied by a variety of cold-water marine organisms and fish. Commonly used enriched sources include salmon, mackerel, sardines, and herring. Another source that is gaining attention is krill. Krill are small crustaceans that are found in all the world’s oceans and include more than 80 species. The species that is used commercially is the Antarctic krill (Euphausia superba). Krill feed on phytoplankton (microscopic algae) and are a primary food source for many larger animals, including baleen whales, penguins and seals. Commercially, krill are used in the aquaculture industry and to produce fishing bait. In recent years, krill meal and krill oil have been studied as sources of protein and long-chain omega-3 fatty acids in pet foods.

Form differences: As omega-3 fatty acid sources, there is an important difference between fish oils and krill. Fish oil fatty acids are found primarily in the form of triglycerides – three fatty acids attached to a molecule of glycerol.

Conversely, the fatty acids present in processed krill are primarily in the form of phospholipids. These structures differ in the presence of a phosphate group in one of the fatty acid positions on the glycerol molecule (Note: We examine omega-3 and omega-6 fatty acids and their use in the body in detail in “Basics of Canine Nutrition”). For our purposes here, it is important to know that phospholipids are the form of fatty acids that are incorporated into cell membranes. This means that they are already present in the form that the body uses, when supplied as krill.

Does this difference matter? This is the question at hand. There is some evidence in human subjects and laboratory animals that the long-chain fatty acids found in krill oil, because they are in the form of phospholipids, may be more efficiently utilized – incorporated into cell membranes – than those supplied by fish oils in the form of triglycerides. The practical implication of this is that the dose that is needed to increase omega-3 fatty acid levels in the body may be significantly lower when supplied as phospholipids (from krill) compared with the dose needed when supplied as triglycerides (fish oil).

As always, the question we ask in The Science Dog is:

“What About Dogs?”

The Study: Researchers at Aker BioMarine Antarctic in Norway asked exactly this question. The researchers designed a study to evaluate the ability of krill meal versus fish oil to increase omega-3 fatty acid status in a group of healthy adult Alaskan huskies (1). A group of 20 dogs was divided into two groups of 10 dogs each. All of the dogs were fed the same complete and balanced commercial dog food throughout the study period. Group 1 was fed a krill meal supplement providing 1.7 grams of EPA/DHA per day. Group 2 was fed a fish oil supplement providing the same amount of EPA/DHA per day. Dog were fed the supplements for a six-week period and Red Blood Cell (RBC) fatty acid levels were measured at baseline, 3 weeks and 6 weeks. (RBC fatty acid levels are a validated and non-invasive method for measuring tissue levels and body status of omega-3 and omega-6 fatty acids).

Results: Several differences between the two supplemented groups of dogs were found:

Total omega-3 fatty acids: The omega-3 fatty acid index increased in both groups of dogs. However, this increase was significantly greater in dogs fed krill oil compared with those fed fish oil (62 % vs. 21 % increase from baseline).
EPA vs. DHA: The change in the krill meal group was driven primarily by EPA (eicosapentaenoic acid), rather than by DHA (docosahexaenoic acid). This occurred because krill provides a rich source of EPA but is lower in DHA than are most fish oil supplements. In contrast, dogs fed fish oil showed a slight by statistically significant increase in DHA levels compared with dogs fed krill meal.
Omega-6 fatty acids: The omega-6 fatty acids (specifically arachidonic acid and linoleic acid) found in RBC membranes decreased in both groups of dogs. For example, the pro-inflammatory omega-6 fatty acid that is incorporated into cell membranes decreased 8.1 % in the krill-supplemented group and 8.5 % in the fish oil-supplemented group.

Take Away for Dog Folks

So what do these results signify in a practical sense? First, these results show that, like fish oil, krill meal supplies a concentrated source of long-chain omega-3 fatty acids to dogs. These data also corroborated studies in other species demonstrating that omega-3 fatty acids were more efficiently supplied by krill oil compared with fish oil, resulting in higher levels of these fatty acids in body tissues. There was a concomitant reduction in omega-6 fatty acids, specifically in arachidonic acid (ARA), which suggests a potential shift towards reduced production of pro-inflammatory mediators.

However, remember that this last step has not yet been demonstrated, nor are there any clinical trials showing reduction in inflammatory disease in dogs fed krill meal or krill oil. (In other words, take care to not over-interpret these results, please…..).

Second, should you feed krill oil (or meal) rather than fish oil? Well, the jury is still out on this one. Both krill and fish oils can effectively increase omega-3 fatty acid status in dogs. Krill may accomplish this more efficiently.

Sustainable? Krill is often promoted as a more sustainable source of omega-3 fatty acids (and possibly an alternative protein source) for dogs due to the use of eco-friendly harvesting. However, others argue that these methods are offset by resource-heavy processing methods used with Krill.

At this point, take these data for what they tell us. Krill is a potentially more sustainable source of omega-3 fatty acids that may be more efficiently utilized by dogs when compared with fish oils.

And that phrase that everyone loves to hear……more research is needed……

Cited Study: Burri L, Heggen K, Storsve AB. Higher omega-3 index after dietary inclusion of omega-3 phospholipids versus omega-3 triglycerides in Alaskan Huskies. Veterinary World 2020; 13:1167-1173. (Note: Authors are employees of Aker BoiMarine Antarctic AS, a Norwegian company that produces krill meal).