Vitamin A, also known as retinol, has an incredible array of functions within the bodies of animals. One of its best-known purposes is to maintain eye health and night vision. However, it is also necessary for healthy teeth, skin, coats, hooves, bones, nerves, kidneys, mucus glands, and adrenal glands.
This vitamin is key to the proper functioning of nearly all immune cells, and it works as an antioxidant, removing substances that have the potential to harm cells. For this reason, vitamin A is important for preventing infections and parasite infestations.
Vitamin A also plays a vital role in reproduction. It is necessary for fertility and conception, as well as proper development of embryos. In mammals, vitamin A ensures healthy mammary glands. In poultry, the vitamin is necessary for a smooth hatch and for chick vigor. In all types of livestock, vitamin A is needed for proper growth.
Beta carotene is a plant pigment which is converted to vitamin A in the gut of many animals. Some animals, such as cattle, do not absorb vitamin A directly from their food, but rely on its precursor, beta carotene. Swine, poultry, and dogs, however, can also use the preformed vitamin A found in animal-derived foods. Cats cannot use beta carotene at all, but must rely solely on animal sources.
By far the best source of beta carotene for grazing animals is green, leafy forage. Hay (particularly legume hay) qualifies provided that it is properly grown and harvested. Beta carotene can be destroyed, however, by poor storage.
Yellow corn has more beta carotene than any other cereal grain. Other sources of vitamin A include organ meat (particularly liver), cod liver oil, egg yolks, and whole milk.
Causes of Deficiency
Because vitamin A is a fat-soluble vitamin, stored in the animal’s fat and in its liver, it takes approximately two to four months to build up a deficiency. Any type of prolonged stress can cause vitamin A deficiency, including disease, parasites, and abrupt changes of diet. Deficiencies in zinc and vitamin E can also lead to a deficiency in vitamin A.
Many animals suffer from vitamin A deficiency after receiving poor-quality diets. This may include extremely processed feeds and feeds that have been stored for long periods of time. Since green forage is the best source of vitamin A for grazing animals, a diet high in grain and low in roughage can lead to deficiency. So can a prolonged spell of drought, which reduces the beta carotene and increases the toxins present in grass.
Chemicals can also interfere with vitamin A synthesis. Common culprits include steroids and other hormone treatments, as well as nitrate contamination of pasture or drinking water.
Symptoms of Deficiency
Symptoms may vary widely.
- Lack of resistance to parasites and infections.
- Night blindness.
- Dry, watering, cloudy, or ulcerated eyes.
- Nasal discharge.
- Pale combs and wattles.
- Harsh coat.
- Ruffled feathers.
- Loss of appetite.
- Pneumonia in young animals.
- Genital and urinary tract infections.
- Infertility/drop in egg production.
- Abortions and stillbirths.
- Young animals born with serious defects leading to death.
- Slow growth.
- Excessive panting at high temperatures.
- Hard mucus membranes which accumulate a cheesy material.
- Difficulty swallowing.
- Swollen brisket, leg joints, and sometimes abdomen.
- Posterior paralysis in young swine.
Symptoms of Toxicity
There are no reported cases of beta carotene toxicity in livestock. Pets may temporarily develop darker coloring in their skin and fur.
When animals are given excessive vitamin A supplementation, however, the following symptoms may be observed:
- Loose teeth in kittens.
- Rough, unkempt coat.
- Fragile and/or malformed bones.
- Irreversible arthritis (particularly in the neck) due to fused joints.
- Appetite loss.
- Birth defects.
- Slow growth.
Vitamin A can be rather dangerous when supplemented on its own. However, its precursor, beta carotene, has been used with success to treat eye problems. Studies also indicate it may have potential in preventing mammary infections in dairy cattle.
Content regarding medical conditions and treatment is provided for general information purposes only, and is not to be construed as legal, medical, or professional advice. Please consult your veterinarian for advice regarding your specific animal’s needs.