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Vitamin A (Retinol) in dog and cat diets

A short guide to the role of Vitamin A (Retinol) in dog and cat nutrition.

Vitamin A (Retinol)

It is a fat-soluble vitamin, which means the body does not excrete its excess in the urine, but stores it in the liver and fatty tissue. It is essential for proper vision (it forms rhodopsin in the retina of the eye), for maintaining healthy skin and mucous membranes, and also for fetal development and the functioning of the immune system [1] [2].

Where it's found: Liver (the main and practically only source of retinol in BARF), egg yolks, full-fat saltwater fish, fish oil (oil from fish liver). The vitamin A content in liver is extremely variable — beef liver contains roughly 16,000–50,000 IU/100 g, poultry liver usually less, and the values fluctuate several-fold between batches [2]. The standard 5% liver in the diet is a starting point, not a rigid rule — what counts is the calculation of the whole mixture [1].

Species difference

Dogs (relative carnivores): They can obtain vitamin A from two sources. They can absorb ready-made retinol from meat, but they can also convert plant beta-carotene (e.g. from carrot) into the active form of vitamin A in their intestines. In practice, on a raw diet rich in retinol from liver, this pathway has only marginal significance, and its efficiency declines with age [2].

Cats (obligate carnivores): They do not possess the enzyme necessary to convert plant carotene. For the cat, carrot is completely useless as far as vitamin A is concerned. The cat must receive in its diet exclusively the ready-made, active form of vitamin A (retinol), which occurs only in animal tissues [3]. This is one of the reasons why liver in a cat's diet is absolutely essential.

Deficiency: In animals fed a properly balanced diet, deficiency occurs very rarely, because the reserves in the liver last for months. It appears most often when feeding muscle meat alone without the addition of liver for many weeks, or with severe intestinal diseases. Symptoms include deteriorating vision at dusk (night blindness), dry and flaky skin, weakened immunity, and in puppies and kittens disorders of bone growth [1].

Excess: In BARF practice this is a more frequent and more important problem than deficiency, because vitamin A accumulates in the liver and is not quickly excreted [1]. Chronic excess leads to painful, irreversible bone changes — especially fusions in the cervical part of the spine (deforming spondylosis), neck stiffness and reluctance to move. Cats are the classic model of this condition in veterinary medicine [4]. The most common cause is the accumulation of retinol sources: liver in the mixture + fish oil or fish liver oil + dried liver treats + supplements. A single larger portion of liver does not cause a catastrophe — the problem is repeated excess over weeks and months [5]. Dried liver treats are a trap: 30–40 g of dried corresponds to 200–300 g of fresh.

Interactions

Vitamin A and vitamin D are both fat-soluble and stored in the liver — a high level of one antagonizes the action of the other. This is another argument for not overdoing it with liver. Vitamin E protects vitamin A from oxidation, so with diets high in liver the requirement for vitamin E rises [2]. Pregnancy, puppies/kittens and liver diseases are situations in which it is worth consulting the recipe with a veterinarian.

Sources

  1. National Research Council (NRC) (2006). Nutrient Requirements of Dogs and Cats, chapter 5 — fat-soluble vitamins. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
  2. Shastak Y, Pelletier W (2024). Pet Wellness and Vitamin A: A Narrative Overview. Animals 14(7):1000. https://doi.org/10.3390/ani14071000
  3. Schweigert FJ, Raila J, Wichert B, Kienzle E (2002). Cats Absorb β-Carotene, but It Is Not Converted to Vitamin A. J Nutr 132(6):1610S-1612S. https://doi.org/10.1093/jn/132.6.1610s
  4. Seawright AA, English PB, Gartner RJW (1967). Hypervitaminosis A and deforming cervical spondylosis of the cat. J Comp Pathol 77(1):29-39. https://doi.org/10.1016/s0021-9975%2867%2980004-5
  5. Morris PJ, Salt C, Raila J et al. (2012). Safety evaluation of vitamin A in growing dogs. British Journal of Nutrition 108(10):1800-1809. https://doi.org/10.1017/S0007114512000128