Creature Companion 2019; October: 44-45.
Anton C. Beynen
Seaweed (gum) in petfood
Seaweeds are macroalgae, plant-like organisms without specialized tissues. Production involves
cultivated crops and some wild seaweed. Marine vegetables can be found in foods, treats and
supplements for dogs and cats. They are declared on the label as seaweed, kelp or
rockweed/Ascophyllum nodosum. Seaweed is lauded as micronutrient powerhouse, but this is
subservient when used alongside or in complete petfood, which by definition meets the target-
animals’ nutrient needs. Some dental treats feature rockweed.
As ingredient listed on petfood, the term seaweed is unspecific, while kelp refers to a mixture of
brown algal species or actually denotes rockweed. The health claims made on seaweed in dog and
cat foods are unsubstantiated. However, rockweed-enhanced treats may moderately slow the
buildup of plaque and calculus, thus reducing the necessity for frequent brushing and/or
elongating the interval between professional teeth cleanings.
Quite some wet petfoods contain seaweed-derived gums that act as thickeners for optimum fluid
stickiness and particle distribution. Those gums are carrageenan, agar and alginate, consisting of
different, heterogeneous carbohydrate chains. Carrageenan is thought to cause bowel
inflammation and cancer in dogs and cats (1-6). This has inspired some manufacturers to market
petfoods with a “no carrageenan” claim (7, 8).
In dry and wet petfood applications, that is at inclusion levels below 0.5%, dried seaweed (gum)
has no known, negative effects on dogs and cats. Testing showed that dietary alginate is harmless
in dogs. Agar and carrageenan most likely are safe petfood additives. Poligeenan, a research
chemical in the form of degraded carrageenan, produces bowel inflammation and cancer,
explaining the confusion and unnecessary concerns over whole carrageenan in petfood (9, 10).
European legislation designates alginate, agar and carrageenan as technological additives in
feedingstuffs, falling within the subclass of emulsifying and stabilizing agents, thickeners and gelling
agents (11-13). Seaweed meal is listed in the catalogue of feed materials (14).
Both kelp and rockweed roughly contain 8% protein in the dry matter, 3% fat, 30% ash, and 60%
carbohydrates. Up to half of the carbohydrates is alginate, while both fucoidan and laminaran
account for one seventh (15-18). Noteworthily, kelp is high in iodine (0.14% in dry matter, 16) and
rockweed in arachidonic acid (0.6%, 17).
Within and between seaweed gums, structurally different polysaccharides are present (15).
Alginates are extracted from brown seaweeds. They are made up of methylated and sulfated, D- and
L-galactose units. Red seaweeds provide agars or carrageenans, which comprise either β-D-
mannuronic and α-L–guluronic acids or sulfated D-galactose and (3,6)-anhydro-D-galactose units.
Fucoidan is a fucose-containing polysaccharide; laminaran is a branched beta-glucan.
In two-bowl, preference tests, dogs received extruded, wheat-based foods without or with 0.3 or
1.0% powdered rockweed (19). The low dose did not affect food intake, but the high dose had a
pronounced, lowering effect. A supplier of rockweed recommends 0.25% as inclusion rate (20) and
maintains that there is no negative effect on palatability (21). The product would also support gut
health, immunity and de-stress in pets (21), but experimental designs and outcomes are undisclosed.
After 50 participants had given their dogs a macroalgae blend for 2-4 weeks, 15 out of the 17
respondents reported improved digestion, coat and skin for the recipients (22). In open,
uncontrolled trials, 60-days oral administration of a kelp mixture to dermatitic and osteoarthritic
dogs was associated with improvement (23). In the two before-and-after comparisons, the seaweed
doses were presumably equivalent to 1.5 and 0.6% in dry dog food.
Rockweed and teeth
Oral administration of Ascophyllum nodosum, versus no treatment or placebo, statistically
significantly reduced progression of dental plaque, calculus, gingivitis and halitosis in dogs (24-26),
but the effect sizes were relatively small. Outcomes in cats were similar (25). In a small-scale,
uncontrolled trial with dog patients given rockweed, regression of plaque and calculus was seen
The control and test dogs (n = 6-30/treatment) were either kennel- or privately-owned, subjected to
baseline dental cleansing or not, and fed the same diet or not, for 42-90 days (24-26). Rockweed, in
powdered or tablet form, was dosed at 33-50 mg/kg body weight per day. Fucoidan might be the
active principle as it inhibits dental-plaque bacteria in vitro (28). It may not survive high-temperature
processing (29, 30).
Gums and digestion
Data for dogs and cats are lacking, but seaweed-gum polysaccharides likely raise the viscosity of
intestinal contents and resist both digestive enzymes and bacterial breakdown (cf. 31-33). Ingested
carrageenan may appear in feces intact (33). The outcomes vary widely (34, 35, Note 1), but it may
be assumed that 0.5% carrageenan in wet food (2.5% in dietary dry matter) reduces apparent
protein digestibility in dogs and cats by no more than 3.5% units. Then, the additive would not
jeopardize the animals’ protein supply in practice (36). Alginate was found to increase protein
digestion in dogs (37, Note 1).
Dried seaweed and seaweed-derived gums are included in (wet) petfood at levels up 0.5%. There is
no evidence for negative effects in dogs and cats. Dogs that ingested tableted rockweed, for 90 days
in an amount equivalent to 0.3% in dry food, gained body weight (26). Feeding dogs on dry food with
15% alginate for 1 year was without adverse effects (38, 39). Such a dog study with agar or
carrageenan appears unperformed.
High agar intakes did not induce negative, chronic effects in rats (40). Rats fed diets containing up to
15% carrageenan did not develop abnormalities, including colonic cancer (41, 42). Poligeenan, made
by harsh acid degradation of carrageenan, produced colonic cancer and ulceration (43-45).
Effects of dietary carrageenan and alginate on apparent food digestion and fecal characteristics in
dogs and cats
% of intake
Ref = reference; D/C = dogs or cats; D = days, duration of feeding (nr = not reported); n = dogs/cats
per dietary treatment; C/A = carrageenan or alginate; C/A, % = % of diet (34) or of dietary dry
matter (35, 37); OM = organic matter; Prot = protein; Fecal characteristics: g/day as is; DM = dry
matter; Score = fecal score on a 1-5 scale, with 1 = hard, crumbly and 5 = diarrhea, liquid.
Control = control diet: 1, not reported; 2, wet diet containing 24.3% dry matter and 0.4%
carrageenan; the other diet contained 41.0% dry matter and 0.8% carrageenan and had almost the
same macronutrient composition of the dry matter, but it is not explicitly stated (35) that the dry
matter of the unsupplemented diets was identical; 3, enteral formula containing 23.8% dry matter
and 0.71% of 1:1 mixture of oat fiber and soy polysaccharide; to produce the test formula, the
mixture was replaced by alginate.
Reference 37 concerns dogs with an ileal cannula. Dietary alginate raised group-mean apparent ileal
digestibilities of organic matter and crude protein from 91.4 to 94.6 and from 80.5 to 90.2% of
Note 2. In a food preference study with dogs, the dry diets, which were based on either animal or
vegetable ingredients, contained 1.5% kelp (46), or rather Ascophyllum nodosum (20).
Note 3. Oral administration of fucoidan and fucoxanthin to aged dogs has been reported to improve
cardiac function (47).
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