Sulfur - S

Sulfur is a macroelement which in the body of the dog and cat does not function on its own, but as part of other compounds — above all the sulfur amino acids (methionine and cysteine), from which keratin of coat and claws, glutathione (the main antioxidant), and taurine are formed [1] [2]. In practice, dogs and cats do not meet their sulfur requirement from inorganic forms — they get it mainly from animal protein. That is why sulfur supply is tracked not separately, but through the sum of sulfur amino acids (methionine + cystine) — see Methionine + cystine.

Where it's found: The best sources are red muscle meat, hearts, eggs and fish — raw materials with a high content of sulfur amino acids [2]. Connective tissues (stomachs, lungs, tendons, skins, cartilage) have a poor sulfur amino acid profile and should not form the protein base of the diet [3].

Deficiency: On a balanced meat diet it practically does not occur. A low sulfur amino acid result in the calculator almost always means too much connective tissue at the expense of real muscle meat — a clear signal of poor protein quality [1]. Symptoms include a dull, brittle coat, slower wound healing and weakened immunity. In the cat the deficiency is more serious than in the dog, because it additionally limits the already weak taurine synthesis [1] [2].

Excess: From natural meat raw materials it is unlikely. The risk concerns supplementation with synthetic methionine: sulfur amino acids are metabolized among others into sulfates, which acidify the urine [3]. In the cat on a raw meat diet the urine is already naturally acidic, so additional acidification with methionine is usually unnecessary and risky — with a predisposition to oxalate (calcium) stones it can aggravate the problem [1].

What to watch for

If the sulfur amino acid bar is low, don't reach for powder — first improve the protein quality in the recipe: increase the share of red skeletal meat, hearts and eggs, and limit collagenous connective tissues [2]. A good supply of sulfur amino acids does not replace the separate monitoring of taurine in the cat — these are related but distinct parameters [1].

Sources

1. National Research Council (2006). Nutrient Requirements of Dogs and Cats. National Academies Press. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
2. Dodd SAS, et al. (2023). Amino acid nutrition in cats and dogs. Journal of Animal Science and Biotechnology 14:19. https://doi.org/10.1186/s40104-022-00827-8
3. Hand MS, Thatcher CD, Remillard RL, Roudebush P, Novotny BJ (2010). Small Animal Clinical Nutrition, 5th Edition. https://www.markmorrisinstitute.org/sacn5.html