Dr A C Beynen* was professor of veterinary nutrition at the Faculty of Veterinary Medicine, Utrecht University, The Netherlands in the period of 1993-2007.
Microalgae are single-celled, aquatic organisms. They use sunlight or nutrient calories as energy source for growth and are cultivated in open-pond or closed-tank systems. Spirulina and chlorella, light-absorbing microalgae, can be found in supplements, treats and complete foods for dogs and cats. Alternatively, such products may contain a macronutrient-burning alga as source of DHA (docosahexaenoic acid).
Spirulina in nutritional products for pets is often positioned as a superfood, thus appealing to nutrient-rich and health-giving. Superfood as qualification is redundant for spirulina in complete food, which by definition meets the target-animals’ nutrient needs. That also holds for spirulina in a supplement or treat fed alongside complete food. Spirulina is frequently touted as immunity and skin supporter, but these and other health claims are unsubstantiated for dogs and cats.
Marketed chlorella tablets and powders for dogs and cats assert to be nutritious, support immunity and detoxify the body. The first claim can be dismissed by grounds for redundancy and the second by lack of research evidence. Chlorella is believed to cleanse dog’s and cat’s body of accumulated, toxic chemicals coming from the environment, processed foods, preventive and therapeutic drugs (1-3). There is neither a theoretical nor experimental basis for ingested chlorella as detoxifier.
Supplements, treats and complete foods featuring DHA-rich algae promise improvements in skin, coat and joint health, immunity, trainability of puppies and brain function of aged dogs. There is no evidence that extra intake of DHA, as sole omega-3, polyunsaturated fatty acid, meets the claims. Particularly, addition of algal DHA to the diet of older dogs did not convincingly enhance their performance in cognitive ability testing.
Dried algae, algal oil, algae meal and extract are listed in the European catalogue of feed materials (4). As a rough guide, autotrophic spirulina and chlorella contain 57% crude protein in the dry matter, 11% crude fat, 8 % ash, 6% crude fiber and 18% soluble carbohydrates (5-11). For the heterotrophic, DHA vehicle, Schizochytrium sp, the values are 11, 51, 9, 2 and 27% (12-15).
Dried spirulina and chlorella reportedly hold about 1% chlorophyll and 0.1% carotenoids (6, 9), but there is a wide variation. Apart from chlorophyll, spirulina also has some 10% phycocyanin as photosynthetic pigment (6, 16). Dry spirulina contains about 2% GLA (gamma-linolenic acid), which is absent in chlorella, while both algae have negligible contents of EPA (eicosapentaenoic acid) and DHA (5, 9, 17). Dry, DHA-rich algae contain about 22% DHA, EPA making up less than 0.6% (12-15).
The soluble polysaccharides in Spirulina platensis mainly comprise glucose and rhamnose (18), but there are species differences (19). Spirulina platensis and Chlorella pyrenoidosa have a high-molecular weight polysaccharide, comprising about 0.75% of microalgal dry weight, differing in glycosyl composition, but sharing high water solubility (20).
The large polysaccharide from Spirulina platensis activated cultured, human monocytes (20), pointing to immunostimulatory capacity. Adding the polysaccharide to the diet of mice, or an algal hot-water extract or phycocyanin to their drinking water, enhanced the production of immunoglobulin A by Peyer’s patches ex vivo (21-23).
In the mouse studies, the administered amounts of spirulina components were equivalent to whole-dried algae contents in dry food of 0.2-1.3%. Four out of 10 complete, dry dog foods with spirulina as ingredient, declare inclusion levels of 0.015-0.1%, while a cat food communicates 0.2%. It is unknown whether the amounts of spirulina in commercial petfood, which presumably concern dried, whole algae, promote immunity and visible health in dogs and cats.
The range of spirulina levels in commercial petfood might be appraised by a specific dog study. Single gamma irradiation lowered white-blood cell counts in dogs. That effect was partly reversed by feeding high-molecular weight polysaccharide from Spirulina platensis at a level equivalent to 0.08% in dry food, but was unaffected by 0.02% (24). Those dietary concentrations correspond with 10.7 and 2.7% whole, dried spirulina.
Some petfoods have added chlorella. A complete, dry dog food declares an inclusion level of 0.2%. In rodents, oral administration of a hot-water extract from Chlorella vulgaris augmented the resistance against an intra-peritoneal infection with Escherichia coli or Listeria monocytogenes (25, 26). The extract dosage was equivalent to 0.9 or 2.8% dried, whole chlorella in dry food.
A small-scale, non-blinded, controlled study suggests that ingestion of chlorella powder may reduce the severity of canine dermatitis (27). The chlorella dosage corresponded with 0.6% in dry food.
Intake of fish oils, providing both EPA and DHA, may ameliorate atopic dermatitis (28) and osteoarthritis (29-31), and modulate immunity indicators in dogs (32). There is no solid proof that dietary DHA improves trainability of puppies (33). In aged dogs experienced on cognitive testing, incorporation of 0.4% dried, whole-cell Schizochytrium sp into dry food inconclusively influenced the outcomes of four different cognitive ability tests (14). The control diet was DHA-free.
Inclusion of 0.4% of DHA-rich algae in dry food has been reported to increase apparent protein digestibility and palatability in dogs (34), but confirmation is desirable. Oil from an undisclosed species of Schizochytrium contains 40% DHA and 12% EPA. That algal oil, included at levels up to 2.9% in extruded dry food, was safe in a gestation-lactation-growth study in dogs (35). Its value as functional ingredient is intriguing.
* List of references is available on request from the author (firstname.lastname@example.org)