What causes lack of vitamin A in animals? - The Environmental Literacy Council (2025)

A vitamin A deficiency in animals arises primarily from an insufficient intake of this essential nutrient, or when the body is unable to effectively absorb or convert it. Specifically, this deficiency occurs when the amount of vitamin A available doesn’t meet the animal’s physiological requirements. This inadequacy can stem from various factors, including dietary deficiencies, impaired absorption, and certain disease conditions. Understanding these causes is crucial for maintaining animal health and productivity.

Dietary Deficiencies: The Primary Culprit

Insufficient Intake of Beta-Carotene

The most common cause of vitamin A deficiency in animals is a lack of beta-carotene in the diet. Animals, unlike humans, obtain vitamin A primarily by converting beta-carotene, a pigment found in green plants, into retinol, the active form of vitamin A. When animals, particularly livestock, don’t have access to green pasture or high-quality forage, they miss out on this crucial precursor.

• Feedlot animals: Cattle and sheep in feedlots, especially those on high concentrate diets without access to green forage, are particularly susceptible.
• Drought conditions: During droughts, the scarcity of green vegetation makes it difficult for animals to meet their beta-carotene requirements.
• Winter months: Similar to drought situations, during the winter when fresh forage is unavailable, animals can experience deficiencies if they aren’t provided with appropriate supplementation or alternative feed sources that contain beta-carotene.

Lack of Preformed Vitamin A

While beta-carotene is the primary source, preformed vitamin A is found in certain animal products like liver, fish, eggs, and dairy products. Diets completely devoid of these products, especially in carnivores fed muscle meat (which is a poor source of vitamin A), can also contribute to deficiency. This is particularly relevant in domestic pets, or in rare cases, in livestock fed unusual or restricted diets.

Impaired Absorption and Conversion

Digestive Tract Issues

Even with adequate dietary intake, vitamin A deficiency can occur if the body cannot effectively absorb nutrients. Conditions like diarrhea and other gastrointestinal diseases can impair the absorption of fats, including fat-soluble vitamins like vitamin A.

Interference with Absorption

Certain medications or substances can also interfere with vitamin A absorption. Mineral oil, cholestyramine, and food products containing olestra can bind to vitamin A and prevent it from being absorbed into the bloodstream. Additionally, some weight-loss medications like orlistat can reduce the absorption of beta-carotene and other fat-soluble vitamins.

Conversion Problems

In addition to absorption, the actual conversion of beta-carotene to vitamin A can be affected by several factors. If the digestive system is compromised, animals might have trouble processing and converting beta-carotene, leading to a functional deficiency.

Disease and Physiological Conditions

Increased Physiological Demand

Certain physiological conditions can increase an animal’s requirement for vitamin A. During periods of growth, reproduction, and lactation, the need for vitamin A increases significantly. If dietary intake doesn’t keep pace with this heightened demand, a deficiency can develop.

Infection and Stress

Animals that are experiencing high rates of infection, especially those leading to diarrhea or diseases such as measles, have a reduced capacity to utilize available vitamins properly. In addition, physiological stress, often a common occurrence in intensive farming environments, can increase the breakdown of vitamin A, leading to a higher need for its replenishment.

Storage Issues

Depleted Liver Stores

Vitamin A is primarily stored in the liver. Healthy animals, particularly cattle, can store enough vitamin A in their livers to last for months. However, when an animal has been on a deficient diet for an extended period, these stores can become depleted, resulting in a deficiency. This becomes a significant issue during periods of inadequate beta-carotene intake, such as during winter or drought.

Frequently Asked Questions (FAQs)

1. What are the primary sources of vitamin A for animals?

The best source of vitamin A is beta-carotene from green vegetation. Animals convert this pigment into vitamin A. Liver, fish, eggs, and dairy products are also good sources of preformed vitamin A.

2. Can animals get too much vitamin A?

Yes, although it is rare in beef cattle. Vitamin A toxicity can occur from excessive supplementation, particularly with raw liver, cod liver oil, or other supplements, leading to symptoms such as drowsiness, vomiting, skin problems, and hair loss. Repeated dosing of cattle at short intervals with high injections of vitamin A should be avoided.

3. What are the signs of vitamin A deficiency in animals?

Signs of deficiency vary but can include night blindness, reduced growth, poor reproduction, impaired immune response, and skin issues. In severe cases, the eye can dry out, tissues may build up in the cornea, which may lead to blindness.

4. How is vitamin A deficiency treated in cattle?

Vitamin A deficiency in cattle is usually treated by injecting them with vitamin A supplements at a rate of 400 IU/kg, as advised by a veterinarian. It’s crucial to supplement when dietary sources are insufficient.

5. Why are feedlot animals prone to vitamin A deficiency?

Animals in feedlots are often fed high-concentrate diets lacking green pasture. This reduces their intake of beta-carotene, leading to deficiencies if not properly supplemented.

6. What role does beta-carotene play?

Beta-carotene is a precursor to vitamin A. Animals convert it into retinol, the active form of vitamin A, making it crucial for various bodily functions.

7. Can hay provide vitamin A to animals?

High-quality hay, especially if green in color, can still contain moderate levels of beta-carotene. This can provide some additional vitamin A, although not as effectively as fresh forage.

8. How do medications affect vitamin A absorption?

Some medications like mineral oil, cholestyramine, and orlistat can interfere with the absorption of vitamin A and other fat-soluble vitamins by binding to them and preventing their uptake.

9. Which animals are most commonly affected by vitamin A deficiency?

Vitamin A deficiency affects all species, but cattle and sheep are often the most susceptible due to their reliance on plant-based diets and intensive farming practices, which can restrict access to green pasture.

10. Is muscle meat a good source of vitamin A?

No, muscle meat (like steak) is not a good source of vitamin A. Liver and other organ meats are much richer sources.

11. What happens if vitamin A deficiency goes untreated?

If untreated, vitamin A deficiency can lead to vision problems, decreased immunity, reduced productivity, and overall poor health, including in severe cases, even death.

12. What are the first signs of vitamin A deficiency in animals?

Night blindness is often one of the first indicators of vitamin A deficiency in animals.

13. Where is vitamin A stored in animals’ bodies?

Vitamin A is primarily stored in the liver, but also in smaller quantities in the kidneys and lungs.

14. Can vitamin A deficiency be cured?

Yes, mild vitamin A deficiency can be treated effectively, often without lasting effects. Treatment typically involves supplementation and adjustments to the animal’s diet.

15. How can carnivores on a limited diet maintain proper vitamin A levels?

Carnivores on limited diets, such as a carnivore diet, should include sources of preformed vitamin A like liver in their diet, or source high-quality grass fed beef, which may contain higher levels of carotenoids, a precursor to vitamin A.