Copper

Recent years have seen more regulation around copper levels in dog food. In Europe, a legal maximum limit now exists (2.8 mg per 100 g dry matter). Copper is crucial for many physiological processes, including enzymatic reactions, neurotransmitter production, collagen formation, and iron absorption. Both deficiency and excess must be avoided. Regulation in the body depends on absorption in the gut, excretion, and interactions with other nutrients. Certain breeds, like Labrador Retrievers, are genetically predisposed to copper accumulation in the liver (copper-associated hepatitis, CAH), leading to liver disease risk. Copper deficiency often manifests as loss of hair pigmentation, reduced fertility, weakened immunity, and connective tissue issues. Copper toxicity can impair liver function and cause hemolysis—breakdown of red blood cells.

Iodine

Iodine is essential for the synthesis of thyroid hormones, which regulate cell activity, growth, and brain development. Insufficient iodine can cause thyroid enlargement and developmental problems. Too much iodine can also lead to thyroid disease, so dog food regulations now impose upper limits. If your dog isn't eating commercial complete food, supplementing with seaweed can help meet iodine needs.

Iron

Iron is important for dogs, and deficiency commonly leads to anemia. Iron occurs naturally in meat and water, so most dogs receive enough in their diet. Vegetarian-fed dogs may need extra monitoring. Pale gums and lethargy could be signs of deficiency—and a vet can test iron levels via a blood test. As with other trace elements, excess iron is also undesirable.

Manganese

Manganese is a component of several enzymes and plays roles in carbohydrate and amino acid metabolism, bone formation, and growth. Sources include whole grains and green vegetables. Symptoms of manganese deficiency can include skin problems, bone weakening, metabolic disorders, and hypertension.

Selenium

Dogs (like all mammals) need the right amount of selenium—enough, but not too much—for proper body function. Selenium acts as an antioxidant, supports thyroid function, and helps in DNA synthesis. It may also play a role in cancer prevention. Selenium toxicity is rare in nature, but it can occur if dogs receive multiple selenium-containing foods or supplements, since the range between minimum and maximum recommended amounts is narrow. Young growing animals have higher requirements. A chronic deficiency is often subtle but may cause reproductive problems or slower recovery from worm infections.

Zinc

Zinc supports many body functions—healthy skin and coat, immune system, digestion, fertility, growth, development, and wound healing. Research shows that commercial dog food rarely falls below recommended minimum zinc levels, but homemade diets are at higher risk of deficiency. There is also an upper legal limit for zinc in dog food, which not all manufacturers always respect. Excess zinc can harm dogs and also contributes to environmental pollution (soil and water).

Sources:

Laura A Amundson, Brent N Kirn, Erik J Swensson, Allison A Millican, George C Fahey. Copper metabolism and its implications for canine nutrition. Translational Animal Science, Volume 8, 2024, txad147, https://doi.org/10.1093/tas/txad147 https://academic.oup.com/tas/article/doi/10.1093/tas/txad147/7505317

Robert A. Wilson, Enrique G. Yanes, Robert J. Kemppainen. Iodine speciation in dog foods and treats by high performance liquid chromatography with inductively coupled plasma mass spectrometry detection. Journal of Chromatography B, Volume 1022, 2016. Pages 183-190, ISSN 1570-0232, https://doi.org/10.1016/j.jchromb.2016.04.002. https://www.sciencedirect.com/science/article/abs/pii/S1570023216302124

J. H. Freeland-Graves, T. Y. Mousa, and N. Sanjeevi. Manganese in Health and Disease, ed. L. Costa and M. Aschner, The Royal Society of Chemistry, 2014, ch. 2, pp. 34-75. https://books.rsc.org/books/edited-volume/1880/chapter-abstract/2462894/Nutritional-Requirements-for-Manganese?redirectedFrom=fulltext

Zentrichová, V.; Pechová, A.; Kovaříková, S. Selenium and Dogs: A Systematic Review. Animals 2021, 11, 418. https://doi.org/10.3390/ani11020418 https://www.mdpi.com/2076-2615/11/2/418

Pereira, A.M.; Maia, M.R.G.; Fonseca, A.J.M.; Cabrita, A.R.J. Zinc in Dog Nutrition, Health and Disease: A Review. Animals 2021, 11, 978. https://doi.org/10.3390/ani11040978 https://www.mdpi.com/2076-2615/11/4/978