Beynen AC, 2019. Microalgae in petfood

Abstract

Microalgae in petfood 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. Composition 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).

Full text

Creature Companion 2019; November: 40, 42.
Anton C. Beynen
Microalgae in petfood
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.
Composition
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).

Spirulina
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% (Note 1). 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.
Chlorella
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 (Note 2).
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
(Note 3).
DHA-rich algae
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, Note 4). 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.
Note 1
In the mouse studies, the administered spirulina fractions contained the high-molecular-weight
polysaccharide (21), water-soluble substances (22) or phycocyanin (23). Immune effects of the
water-soluble substances (22) and phycocyanin (23) were determined in mice immunized by oral

administration of a crude shrimp extract or ovalbumin-entrapped microparticles. Immune
stimulation by the water-soluble fraction was much greater for lymphoid cells from spleen and
mesenteric lymph nodes than for those from Peyer’s patches (22).
The applied doses of the spirulina fractions can be converted into equivalents of dietary levels of
whole, dried spirulina. However, the microalga may also contain immunomodulatory components
other than those captured in the tested fractions. Dose dependency of the immune effects was not
addressed, implying that the calculated spirulina equivalents likely do not represent the lowest
effective dietary concentrations for mice. Compared with mice, dogs and cats may be more or less
sensitive to the spirulina fractions. Thus, the calculated dietary equivalents of whole spirulina only
provide a rough orientation towards the immunostimulatory impact of petfoods featuring the
microalga.
In one study (21), the high-molecular-weight polysaccharide fraction from spirulina was fed at a level
of 10 mg/mouse.day. That amount is equivalent to dry food containing 1.3% whole, dried spirulina.
The calculation is as follows: 10 (mg extract/mouse.day) x 100/15 (extract represented 15% of
whole, dried spirulina) x 1000/5 (dry food intake = 5 g/mouse.day) = 13333 mg/1000 g = 1.3 g/100 g.
Another feeding study with mice (22) used a hot-water extract of Spirulina platensis. The diluted
fraction was supplied in place of drinking water. The amount drunk was 3.4 ml/mouse.day, which is
equivalent to consumption of dry food containing 0.7% whole, dried spirulina. The calculation is as
follows: 3.4/60 (60-fold diluted extract) x 1000/1.55 (1000 mg dry spirulina matched 1.55 ml extract)
x 1000/5 (dry food intake = 5 g/mouse.day) = 7312 mg/1000 g = 0.7 g/100 g.
Phycocyanin was extracted from spray-dried Spirulina platensis, dissolved in water to a
concentration of 0.05% and given to mice as drinking water (23). The intake of phycocyanin was
equivalent to the feeding of a dry food containing 0.2% whole, dried spirulina. The calculation is as
follows: 0.5 (mg phycocyanin powder/ml) x 3 (fluid intake, 3 ml/mouse.day) x 80/100 (purity of
phycocyanin powder was 80%) x 100/10 (phycocyanin content of dry spirulina is 10%) x 1000/5 (dry
food intake = 5 g/mouse.day) = 2400 mg/1000 g = 0.2 g/100 g.
Note 2
Through stomach tube, mice and rats received daily, per kg body weight, 1000 mg lyophilized, hot-
water extract from Chlorella vulgaris (25, 26). The dry extract contained 39.5 g carbohydrates/100 g.
Thus, 1 g dry extract is equivalent to 2.2 g (39.5/18) whole, dried chlorella. It is assumed that a 20-g
mouse and 250-g rat consume 5 and 20 g dry food/day. The dosages in mice (20/1000 x 2.2 x 100/5)
and rats (250/1000 x 2.2 x 100/20) correspond with 0.88 and 2.75% whole, dried chlorella in dry
food.
Note 3
The dogs received 0.1 g chlorella powder per kg body weight (27). This amount corresponds with
0.6% in dry food, assuming an intake of 16.7 g dry food per kg body weight.
Note 4

Dogs fed a diet without or with 0.4% dried, whole-cell Schizochytrium sp were subjected to
assessment of cognitive function (14). After a wash-in period of 51 days, the two diet groups
underwent five tests over the next 124 days. The tests were as follows: a retest on delayed-non-
matching-to-position, (RDNMP), concurrent discrimination learning (CDL), contrast sensitivity
learning (CSL), variable contrast discrimination (VCD) and retention of concurrent discrimination
learning (RCDL). Each dietary group had 12 dogs aged 9-11 years.
All cognitive function tests use a food reward to motivate dogs to learn the tasks. The DNMP test
measures the ability to learn discriminating between different objects and their positions. The CDL
test addresses the dog’s ability to learn recognizing different pairs of objects. The CSL test was used
to measure contrast sensitivity as an index of visual processing ability. The dogs were tested at
progressively lower contrasts (CSL) or at variable contrasts (VCD).
The RDNMP test did not show a diet effect. Repeated measurements within the CDL tests produced
unsystematic diet differences for the dog’s responses. Two out of the 7 CDL sessions yielded a
significant diet effect, but the multiple comparisons were not taken into account by reducing the
preset P value. The RCDL test did not reveal a diet effect. The algal-fortified diet was found to reduce
the number of errors in the CSL test, but only after the removal of so-called non-responders. That
approach may have introduced selection bias, especially because it was unknown whether a
response or non-response was caused by random within-animal fluctuation or by true/repeatable
differences in responsiveness between individual animals. There was no convincing evidence for a
diet effect in the VCD test; there seemed to be diet effects at two intermediate contrast levels, but
not at the lower and three higher contrast levels.
Note 5
Analysed concentrations of heavy metals in spirulina products were low (36).
Note 6
In cats fed a high-cholesterol diet, administration of concentrated Spirulina plantensis by oral gavage
lowered serum cholesterol levels (37). The spirulina doses were 0.5 and 1.0 g/kg body weight.day.
Those doses would be 3.3 and 6.6% dried spirulina in dry food for a 4-kg cat consuming 60 g
food/day. In feline, bronchoalveolar lavage macrophages, a water-soluble extract from Spirulina
platensis enhanced phagocytic function (38).
Note 7
In dogs fed dry diets containing either 13% beef tallow or 13% of soybean oil plus DHA-rich algae,
oxidative stress markers were not different (39). The composition of the oil-algae mixture is
undisclosed. A communication in abstract form concludes that feeding unextracted
Aurantiochytrium limacinum microalgae for 15 days was without negative effects on health in
mature dogs (40). The dietary inclusion percentage is not reported. A paper suggests that dietary
DHA induces beneficial changes in the canine electroretinogram (41). The study was uncontrolled
and involved three dogs fed a diet containing 0.4% DHA-rich algae for 30 days.
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