Folic acid (Vitamin B9)

It belongs to the water-soluble vitamins and is responsible for DNA synthesis and rapid cell division — especially where tissues renew the fastest: in the bone marrow and the intestinal mucosa [1]. It forms a tight duo with vitamin B12 — the two are always interpreted together. The natural, active form present in tissues is folates; "folic acid" is the synthetic form from supplements. Vitamin B9 is very unstable — it is destroyed by heat, light and long freezing (cooking meat can destroy up to 90%) [2].

Where it's found: Brewer's yeast, liver (the richest source), kidneys and egg yolks.

Deficiency: Rare on a raw diet with offal. It causes macrocytic anaemia (large, immature blood cells). A deficiency in a pregnant bitch or queen drastically increases the risk of cleft palate and neural tube defects in the offspring [4]. An important diagnostic clue: if the diet contains offal and the result still comes out low, the problem usually lies not in the bowl but in the gut. High folic acid with simultaneously low blood B12 is the classic picture of small intestinal bacterial overgrowth (SIBO) [2].

Excess: Because it is a water-soluble vitamin, its excess is efficiently excreted in the urine [3].

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. Hand MS, Thatcher CD, Remillard RL, Roudebush P, Novotny BJ (2010). Small Animal Clinical Nutrition, 5th Edition. https://www.markmorrisinstitute.org/sacn5.html
3. Merck Veterinary Manual. Nutritional Requirements of Small Animals. https://www.merckvetmanual.com/management-and-nutrition/nutrition-small-animals/nutritional-requirements-of-small-animals
4. Domosławska A et al. (2013). Folic acid supplementation decreases cleft palate incidence in Pug and Chihuahua puppies. https://pubmed.ncbi.nlm.nih.gov/23691573/