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Magnesium - Mg in dog and cat diets

A short guide to the role of Magnesium - Mg in dog and cat nutrition.

Magnesium - Mg

In the body it works closely with calcium and phosphorus — about 60% of magnesium is found in bones and teeth. While calcium is responsible for muscle contraction, magnesium enables their proper relaxation. It is a cofactor for hundreds of enzymatic reactions, supports nerve conduction, and plays a key role in energy metabolism at the cellular level (ATP production) [1]. The NRC standard for an adult dog is about 150 mg / 1000 kcal ME (minimum 45 mg) [1].

Where it's found: Red meat (beef, game, lamb), hearts (especially beef and lamb), kidneys, and fish. Raw meaty bones and cartilage tissue provide a certain amount, but their excess paradoxically lowers magnesium absorption.

Deficiency: Resulting directly from too little magnesium in a meat-based diet is rare; most often it is a secondary effect of chronic diarrhea or kidney disease. In the calculator, a magnesium deficiency with correct calcium and phosphorus almost always means that the diet has too little red meat and hearts relative to bone — this is a better "sensor" of recipe quality than the Ca:P ratio alone [2]. The solution is correcting the composition, not supplementation.

Excess: In animals with properly functioning kidneys, dietary excess does not occur — the body efficiently excretes magnesium in urine [1]. Excess is practically possible only from supplements: it then causes diarrhea, and in extreme cases lethargy.

Species difference — urine and stones

In cats, magnesium stirs more emotion than in dogs because of its role in the formation of urinary stones. The historical "magnesium = struvite" panic, however, concerns mainly dry foods — a raw meat diet naturally acidifies the urine, which drastically reduces this risk [3]. What's more, overly aggressive lowering of magnesium in a cat with acidic urine may paradoxically favor oxalate stones instead of struvite ones [4]. Don't cut magnesium by force — hydration, pH, and overall urine balance are more important; a check-up urine test 1–2 times a year is good practice regardless of diet.

What to watch for

Excess calcium from bone competes with magnesium for the same transporters in the gut (TRPM6/TRPM7), so a diet with a lot of bone (above 15–20%) can lead to a functional magnesium deficiency despite its presence in the bones themselves [1]. More on the proportion in the article calcium:phosphorus ratio. Diuretics (e.g. furosemide) increase magnesium excretion — with ongoing pharmacotherapy or kidney disease, the magnesium balance is worth consulting with the attending veterinarian. If supplementation is necessary, glycinate is better tolerated than citrate or magnesium oxide.

Sources

  1. National Research Council (2006). Nutrient Requirements of Dogs and Cats, Chapter 7 — Minerals. National Academies Press. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
  2. Hand MS, Thatcher CD, Remillard RL, Roudebush P, Novotny BJ (2010). Small Animal Clinical Nutrition, 5th Edition. https://www.markmorrisinstitute.org/sacn5.html
  3. Osborne CA, et al. (1984). Treatment and prevention of feline struvite urolithiasis. https://pubmed.ncbi.nlm.nih.gov/6377667/
  4. Lekcharoensuk C, et al. (2001). Association between dietary factors and calcium oxalate and magnesium ammonium phosphate urolithiasis in cats. JAVMA 219(9):1228-37. https://doi.org/10.2460/javma.2001.219.1228