Vitamin A is a fat soluble vitamin which accumulates if overdosed. It has multiple functions within the body including Vitamin A helps in the formation and maintenance of healthy teeth, skeletal and soft tissue, mucous membranes, and skin.  Vitamin A is stored in the liver, and is released in small amounts as it is needed.

Plants don't actually contain vitamin A but carotin. Vegetables such as carrots are high in carotenoids & most animals, including  humans are able to convert carotene from plants into active vitamin A. Cats however are unable to do this as they lack the necessary enzyme, and therefore need to obtain vitamin A from animal tissue, especially liver.

Cats fed a diet containing too much  vitamin A can be harmful to cats & result in hypervitaminosis A.

What are the symptoms of vitamin A toxicosis?

Chronic cases can show ankylosis fusion of cervical vertebrae & elbow joints, making grooming painful & therefore cats may have an unkempt appearance.

Which foods are high in Vitamin A?

Liver, cod liver oil & vitamin supplements are all common causes of hypervitaminosis A in cats. According to Neils Pederson in his book Feline Husbandry - Diseases & Management in the Multiple Cat Household pet mixes obtained from butchers may also on occasion be a cause as they often contain high amounts of liver.

How is it diagnosed?

A diagnosis will be made by obtaining a dietry history & clinical signs. Your veterinarian may wish to take x-rays to check the condition of the cervical spine & forelimbs.

How is it treated?

Switching your cat to a nutritionally satisfactory diet. Bony changes are generally irreversible, however other symptoms should resolve once a proper diet is fed.

Placing food & water bowls on a platform may ease pain for your cat.

Your veterinarian may prescribe anti-inflammatories or analgesics.

References:

[1] The Feline Patient - Gary D. Norsworthy, Mitchell A. Crystal, Sharon K. Fooshee & Larry P. Tilley.