Seaweeds for animal health

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Seaweeds and kelps are proving to be powerful tools for skin, hoof and coat health, digestive improvements, and more.

Seaweeds have been an important component of mammalian diets throughout evolutionary history. They provided the one sure way for humans to avoid the goiter and cretinism caused by iodine deficiency – and they have proven useful for companion animal health as well. Knowing why, when and how to use quality seaweeds can you help best deliver the benefits of the powerful nutrients they contain.

“Seaweed” is a general term for marine macro-algae. Most of the earth’s oxygen comes from seaweeds.1 Phycologists, the scientists who study macro-algae, divide them into three groups: brown algae, red algae and green algae, which together comprise over 20,000 different seaweeds. Names for marine ocean macro-algae mentioned in recent IVC Journal articles include “sea vegetable”, “kelp”, “bladderwrack” and “fucus”. Most of the seaweed used in pet foods and supplements are brown algae from the Laminaria and Fucus families.

How seaweeds differ from land plants

Land plants draw only on the limited resources of the footprint of soil in which they are growing. In contrast, seaweeds collect nutrients through their fronds from the abundant resources in circulating seawater. The fronds of seaweeds are like plant leaves and the holdfasts are like the roots of terrestrial plants. While land plants use roots to absorb nutrients, sea plants use their fronds. This absorption method gives seaweeds a nutrient profile advantage because they are such powerful collectors of the minerals and phytonutrients in the areas where they grow. Ocean water is literally the lifeblood of the planet, containing all essential nutrients in similar ratios to those in the mammalian bloodstream.2

Thus, seaweeds can deliver a very consistent and powerful mineral profile. In turn, there are vast differences in the minerals and biochemicals each species of seaweed collects and stores. The difference between land and sea plants makes seaweeds a more powerful source of micronutrients and phytonutrients, providing they are properly selected, harvested and processed to retain the targeted nutrient profile.

Knowing the genus and species of the “kelp” or “seaweed” you are using can guide you to its nutrient content. However, feed labeling laws do not require species identification and allow broad terms like “seaweed” and “kelp” in ingredient panels. The term “seaweed” can refer to any marine macro-algae, while the term “kelp” is permitted to include any Laminaria or Fucus species, according to feed control officials.

Evaluating quality

What about ocean pollution, radiation, heavy metals, sustainability and quality? How do you know what you are getting? Look for sources harvested from clean waters in remote locations, and that are quickly processed and dried. USDA Organic certification is one way to assure site and processing have been inspected for cleanliness and sustainability.  Kosher certification of the original harvest is another way to assure third party inspection for purity.

Some harvest sites are richer in baseline nutrients; these include bays with geothermal vents and mineral-rich estuaries or rivers. This converts to higher nutrients in the harvestable seaweed. Rapid collection and drying are important because many of the minerals, including iodine, are freshwater soluble and can be washed away if improperly handled.3 Carefully reducing the moisture content to less than 10% helps assure stability and deliverability to animals.

Ascophylum nodosum, a brown Fucus seaweed growing in the tidal zones of the North Atlantic from New England to Canada, Iceland and northern Europe, is the most common species harvested for animal nutrition. Harvest methods range from hand-cutting with a seaweed knife, to custom vacuum cutters, to mowing (like cutting hay) at mid-tide.  Thousands of tons of wet wild harvested Ascophylum are dried using methods such as outdoor windrowing (similar to drying hay in the field), high-temperature drum drying, and lower temperature conveyor belt drying using geothermal heated air. The highest quality, most consistent, effective and sustainable products rely on mapping the beds, mowing on a four to five-year cycle, and converting geothermal energy to hot air for controlled drying.

What’s in seaweed?

Interestingly, macro-algae or seaweeds are most notable as a source of micro-nutrients, including over 60 mineral elements.

Iodine: Seaweeds are historically known as a rich source of iodine, an essential nutrient for thyroid and metabolic health. Iodine content can range from 50 ppm in some of the fast-growing seaweeds, such as red algae of the genus Pyropia (used for sushi nori), to 7,500 ppm in true deep-water kelps like Laminaria digitata. The range for Ascophylum is 300 to 1,200 ppm. Consistent and reliable delivery of a uniform quantity of iodine depends on careful harvest and post-harvest handling and drying. Some suppliers provide detailed specifications and analysis as well as custom blending and formulations to uniformly target iodine delivery levels. Iodine in kelp is present as iodide,4,5 which is easily absorbed.

Too much or too little iodine in the diet can cause a range of problems, including goiter, hyperthyroidism and hypothyroidism, infertility, and cognitive dysfunction.6

Iodine is an essential nutritional element required in very small amounts by animals. It is a constituent of the thyroid hormones thyroxine (T4) and tri-iodothyronine (T3), which play a major role in cell differentiation, growth and development in growing animals and in the regulation of metabolic rates in adult animals. Clinical signs of iodine deficiency include goiter (enlargement of the thyroid gland), alopecia (hair loss), dry sparse hair coat, and weight gain. An all-meat diet can produce iodine deficiency.7

Too much iodine can be toxic. Clinical signs may include excessive lacrimation, salivation, nasal discharge, and a flaky dry skin. Paradoxically, goiter can be a sign of iodine excess as well as deficiency. High plasma concentrations of iodine can inhibit the production of thyroid hormones by the thyroid gland.

Seaweed supplements should be correctly dosed to obtain the most benefits from their nutrient content (see below). Routine inclusion of seaweed is easiest when it is used as an ingredient in a reliable prepared food. But it can also be added, top-dressed, or in limited cases, provided as a free-choice supplement. Assuming a guaranteed and consistent analysis of 750 ppm, kelp should make up a very small amount of the total dry ration. For dogs and cats, we are talking about 0.25% of their dry matter intake, 0.1% for horses, and 0.5% for goats and chickens. Eggs from chickens fed kelp show darker yolks and higher nutrition including iodine.8 Rabbits are special, with a minimum iodine requirement of only 0.2 ppm of diet.9 The iodine requirement for any animal will be higher if the diet includes substantial amounts of cabbage or other Brassica species, which contain natural goitrogens and increase the need for iodine.10

Trace minerals and complex phytonutrients: The vast array of 60 other trace minerals and complex phytonutrients found in seaweeds is incredibly valuable to animal health. Complex bioactive compounds such as polysaccharides promote digestive activity and immune function. Trace levels of vitamin E have been attributed to improved conception rates.

Along with iodine, seaweeds can help with subtle dietary deficiencies, providing very trace quantities of a range of micronutrients. Consider selenium. Kelp accumulates selenium from seawater, and converts as much as 85% of it into organic selenium species11 of high biological activity. In animal studies, kelp has been found to protect against the mammary carcinogenic effect of dimethylbenz[a]anthracene (DMBA).12 These findings suggest that selenium may be responsible for the low incidence of breast cancer in Japanese women, who consume a diet containing iodine-rich and selenium-containing seaweed.13,14

Seaweed is most useful as a baseline preventative nutrient source in the diet. In some cases, it is also an effective treatment when specific problems indicate thyroid iodine deficiency.

Reports from clinical practice15

Kelp, specifically A. nodosum, is recommended by leading holistic veterinarians as a supplement in homemade diets for dogs and cats, and by large animal vets as a nutritional supplement for poultry, cattle, goats, alpacas and horses.  It is one of the few dietary ingredients that contains essential iodine for the thyroid gland and immune system. Many commercial and raw food diets, including The Honest Kitchen, Sojos, and Fresh Pet, use kelp as a source of natural iodine rather than the synthetic sources such as calcium iodate or potassium iodide found in commercial kibble.

Many practitioners realize that seaweeds are different than other green supplements because they deliver different nutrients from land vegetation and microalgae grown in fresh water. Because of their concentrated trace minerals, only a small quantity is needed, and seaweeds are appropriate for daily use. Freshwater microalgae and land plants like alfalfa have their own health benefits and can be used along with seaweed species for veterinary patients.

  • Most practitioners recognize that low thyroid function is rampant in our canine population. Many of the problems we see daily, such as skin conditions, allergies, obesity and even seizures, are related to low thyroid function. The usual blood tests are poor at detecting early thyroid dysfunction. Dr. Jean Dodds notes that kelp can be used to aid in correcting hypothyroidism. Providing the essential nutrients of iodine and selenium for optimal thyroid gland function is critical for returning the animal to health before irreversible changes occur.
  • Practitioners also recognize that along with the benefits seaweed offers in the daily diet as a source of iodine and trace minerals, it can additionally be used to help treat disease conditions in veterinary patients. The salty taste is valued in Chinese Food Therapy for therapeutic support. For example, Dr. Connie Dinatale has used red algae seaweed yezoensis L (nori) to shrink lipomas in her food therapy practice. The salty taste of seaweed enhances palatability and is well accepted by patients of all species.
  • Cynthia Lankenau states that kelp is a balanced supplement with a strong Yin quality, but also a strong Qi moving ability. In particular, it is a Kidney Qi mover with a Spleen Qi mover, and cleanses lymphatics. She finds it beneficial for dogs with lymphoma, congestive heart failure, diabetes, renal dropsy and poor coats. Horses with founder benefit from an improvement in the lamina of the hoof. Dr. Lankenau’s alpaca clients have stated that kelp species such as Ascophyllum nodosum improves the fiber quality of the alpaca diet.
  • Other practitioners like kelp because of its benefits to cancer patients. As holistic practitioners, we know that giving patients the fuel they need for a fully functioning immune system is critical to managing every disease, including cancer.
  • Rick Palmquist shares the case of an aged dog that was mauled by a coyote. After a protracted recovery, the dog’s coat was poor and his hair did not grow back. His thyroid tests were below normal. When a small amount of kelp was added to the dog’s diet, his hair began growing back darker and thicker, within two weeks.
  • Barbara Royal finds kelp especially useful in younger patients that tend to be overweight after spaying or neutering. She feels that removing the gonads, which are important endocrine organs, leads to a system-wide imbalance of many other organs and endocrine tissues, which must compensate for the rest of the patient’s life.

Holistic veterinarians want the purest available source of kelp for their patients. Kelp that is certified organic and carefully harvested from colder ocean waters is more likely to be a reliable product that does not vary in quality.

All in all, seaweeds and kelps are proving to be powerful and useful tools for skin, hoof and coat health, digestive improvements, and even improved conception rates. Supporting the thyroid gland with quality kelp allows the endocrine and immune systems to function at their best to maintain wellness and resist disease.


1Hall J. “The Most Important Organism?” 2011 [cited 2017 4 August]; Available from

2Thompson DJ. “Seawater: A blood plasma substitute?” Nexus Magazine, 2006. 13(6).

3Teas J, et al, “Variability of iodine content in common commercially available edible seaweeds”. Thyroid, 2004. 14(10): p. 836-41.

4Kupper FC, et al. “Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry”. Proc Natl Acad Sci U S A, 2008. 105(19): p. 6954-8.

5Lin L, Chen G, Chen Y, Determination of iodine and its species in plant samples using ion chromatography-inductively coupled plasma mass spectrometry” Se Pu, 2011. 29(7): p. 662-6.

6Office of Dietary Supplements National Institutes of Health. “Iodine — Fact Sheet for Health Professionals”. June 24, 2011 [cited 2017 August 3]; Available from

7National Research Council, Nutrient Requirements of Dogs and Cats. 2006, Washington, DC: The National Academies Press.

8Jacob J. “Seaweed in Poultry Diets” 2015  [cited 2017 4 August]; Available from:

9National Research Council Committee on Animal Nutrition, “Nutrient Requirements of Rabbits”, 1977, National Academy Press.

10Chesney AM, Clawson TA, Webster B. “Endemic goitre in rabbits. I. Incidence and characteristics”. Bull Johns Hopkins Hosp, 1928. 43: p. 261-277.

11Yan X, et al. “Enriched accumulation and biotransformation of selenium in the edible seaweed Laminaria japonica”. J Agric Food Chem, 2004. 52(21): p. 6460-4.

12Maruyama H, Watanabe K, Yamamoto I. “Effect of dietary kelp on lipid peroxidation and glutathione peroxidase activity in livers of rats given breast carcinogen DMBA“. Nutr Cancer, 1991. 15(3-4): p. 221-8.

13Smyth PP. “The thyroid, iodine and breast cancer”. Breast Cancer Res, 2003. 5(5): p. 235-8.

14Cann SA, van Netten JP, van Netten C. “Hypothesis: iodine, selenium and the development of breast cancer”. Cancer Causes Control, 2000. 11(2): p. 121-7.

15Clinical Practice Interviews: Dr. Constance Dinatale, Veterinary Acupuncture and Complementary Therapy, Winter Park, FL; Dr. Cynthia Lankenau, Holistic Center for Veterinary Care, Coldon, NY; Dr. Rick Palmquist, Centinela Animal Hospital, Inc., Inglewood, CA; Dr. Barbara Royal, The Royal Treatment Veterinary Center, Chicago, IL; Dr. Jean Dodds, Hemopet, Garden Grove, CA.

Kelp feed rates for companion animals

Based on a kelp product with an iodine content of 750 ppm

Ideal application is by inclusion in formulation, but controlled dosing is acceptable.

*⅛ oz = ¾ tsp; ¼ oz = 1½ tsp; ½ oz. = 1 tbspNational Research Council recommended iodine daily allowance range.

Generally not recommended for nursing young when the mother is already on kelp.

Dogs: Add kelp at 0.25% of Dry Matter Intake (DMI), sprinkle on or mix into food daily.

Cats: Add kelp at 0.25% DMI, or sprinkle a pinch of kelp on food daily. Reduce rates if the food or supplement already meets iodine requirements.

Horses: Mix in feed at 0.1% of Dry Matter Intake (DMI). Feed ¼ oz of kelp per 500 lbs of body weight, generally not to exceed ½ oz per head per day. Mix into grain ration or apply as top dressing. Reduce rates if your feed or feed supplement already meets iodine requirements.

Goats: Mix in feed at 0.5% of Dry Matter Intake (DMI). Feed 1/4 oz of kelp per 50 lbs of body weight. Kelp can also be fed free choice, alone or with salt.

Chickens: Mix in feed at 0.5% of Dry Matter Intake (DMI) or mix 4 oz of kelp into 25 lbs of grain ration, or apply as top dressing.

Bill Wolf began harvesting seaweeds in 1971 while studying renewable resources with Buckmoinster Fuller. Wolf founded and is president of Thorvin Kelp (, leading supplier of seaweed ingredients. Bill also operates an organic farm in Appalachia and is President of Wolf, DiMatteo+Associates (, which consults on organic projects with companies and governments. Wolf served as President of the Organic Trade Association (OTA) and is founding President of the Organic Materials Review Institute (OMRI).