It is a fat-soluble vitamin, which means that the body stores its excess in the liver and fatty tissue. It is necessary for proper vision (forms rhodopsin in the retina), maintaining healthy skin and mucous membranes, as well as for the development of fetuses and the functioning of the immune system. [1].
What it contains: Liver, cod liver oil (fish liver oil), egg yolks, full-fat sea fish.
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 carrots) into the active form of vitamin A in their intestines.
Cats (obligate carnivores): They do not have the enzyme necessary to convert plant carotene. For a cat, carrots are completely useless in terms of vitamin A. The cat must receive in its diet only the ready-made, active form of vitamin A (retinol), which is found only in animal tissues [2].
Deficiency: In animals fed a properly balanced diet, deficiency is very rare. It most often occurs when feeding only muscle meat without the addition of liver or with severe intestinal diseases [1].
Excess: Most dangerous in cats, which are at high risk of hypervitaminosis A, most often due to feeding them too much raw liver, which leads to painful stiffening of the spine (spondylosis) and joints [3].
Sources
- 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
- 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
- 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