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Vitamin A
Vitamin A occurs in three forms; retinol, retinal, and retinoid acid. It is most well known for retinol’s imperative role in ensuring normal vision in mammals however retinoic acid is important in altering the expression of genes through nuclear receptors. The precursors for vitamin A are beta-carotenes which get converted to vitamin A, predominantly in the liver. Cats rely on preformed vitamin A in the diet as they are unable to carry out the conversion of beta-carotenes to vitamin A. The AAFCO vitamin A recommendations are 6668 IU/kg for a feline in a growing or reproductive state and 3332 IU/kg for adult maintenance. There is a maximum vitamin A intake of 333,300 IU/kg which is to ensure toxicity doesn’t occur. Chronic vitamin A toxicity in felines is distinguished by the prevalence of new bone formation on already formed bone, specifically on the cervical vertebrae. This can cause stiffening of the joints, deformities as well as crippling within cats.