Hypervitaminosis A

Question 1

Explain why vitamin A is an essential nutrient in cats

Answer 1

Cats are able to absorb carotenoids but cannot convert them to the active form of vitamin A because they lack an enzyme
- preformed vitamin A occurs naturally in animal tissues where high levels occur within the viscera
- on a prey diet, it would be redundant to convert carotenoids when the preformed vitamin is already present in the diet

Question 2

What is vitamin A

Answer 2

Vitamin A is a lipid soluble vitamin and can become toxic if given in large doses

Question 3

What is the main cause for excess vitamin A

Answer 3

Vitamin A toxicity occurs in cats given mainly all liver diets or given high dosages of vitamin A supplements (e.g., cod liver oil)

Question 4

What are the cat’s mechanisms to protect himself against hypervitaminosis A

Answer 4

Cats have developed protective mechanisms for minimizing vitamin A toxicity, since animal viscera have a particularly high content of this:
- they transport vitamin A as retinyl esters and are able to excrete large amounts of these in the urine
- they are able to store higher concentrations of vitamin A in their liver, and a small amount in their kidneys

Question 5

What are the characteristic clinical signs of hypervitaminosis A

Answer 5

Hypervitaminosis A is characterized by:
- formation of exostoses on cervical vertebrae causing ankylosis (cervical stiffness and forelimbs lameness occur early)
- deformity
- crippling
- often sit on their hindlimbs in a “kangaroo” posture