One of the best-known roles of vitamin D (calciferol) is its function in calcium and phosphorus absorption. These two minerals are essential for bone growth, so it naturally follows that vitamin D is key to skeletal health.
However, vitamin D is also necessary for proper hormone function. In this role, it helps regulate immune response, insulin secretion, and blood calcium levels.
Two other important functions of vitamin D are carbohydrate metabolism and gene expression, which translates into embryonic growth.
Vitamin D is the sunlight vitamin. Substances in the animal’s skin are converted to vitamin D when exposed to ultraviolet light. How much sunlight an animal needs in a day to supply its vitamin requirements depends on the intensity of the sun and on the amount of hair or fleece covering the animal. Dogs and cats are relatively inefficient at synthesizing vitamin D from sunlight.
Forages are actually a poor source of vitamin D when they are green and growing. When the plant dies, however, the vitamin is formed in the leaves exposed to sunlight, thus making sun-cured hay a good source of vitamin D for grazing animals.
For animals such as swine and poultry, an animal-derived source of dietary vitamin D is far more effective than a plant-derived source. Good sources include whole milk, cod liver oil, and freeze-dried fish meal. Irradiated yeast is also high in vitamin D.
Ideal sources of vitamin D for pets include eggs, liver, fish, fish oils, and dairy products. Seaweed is one of the few good plant sources.
Causes of Deficiency
A vitamin D deficiency is highly unlikely in animals kept outdoors, although it can happen in extremely high latitudes where there is less sunlight. Otherwise, a vitamin D deficiency is usually a sign that something else is wrong, such as parasite infestation, organ damage, or moldy or rancid feed. Long-term use of anticonvulsant drugs is also linked to vitamin D deficiency.
Animals housed indoors must receive vitamin D supplementation of some type. Standard corn and soy rations will not meet their requirements. Hay will only suffice if it is leafy and has been cured in the sun.
Also, recent discoveries suggest that there may be a number of genetic defects that would impair vitamin D synthesis in livestock. Little is known on this topic at present.
Failure to provide a dietary source of vitamin D is another cause of deficiency in cats and dogs—these animals cannot meet their nutritional requirements from sunshine. And for owners who are feeding vitamin D supplements, let the buyer beware! Not all supplements on the market are equally effective (natural sources of vitamin D are far safer, anyway).
Symptoms of Deficiency
- Reduced immune function.
- Lack of appetite.
- Inability to close mouth.
- Failure of adult teeth to appear in kittens.
- Weak teeth.
- Harsh coat.
- Poor feathering.
- Abnormal bands on feathers in colored breeds of poultry.
- Swollen, painful joints.
- Pliable beaks and claws.
- Bowed legs.
- Dragging hind feet.
- Muscle pain.
- Difficulty standing.
- Labored breathing.
- Reduced egg production.
- Dead, weak, or deformed offspring.
- Decreased milk production.
- Milk fever.
- Failure to grow.
Symptoms of Toxicity
Vitamin D toxicity in animals is typically due to oversupplementation (particularly with synthetic vitamins), although pets can also suffer from excess after eating some rodent baits, human medications, and unbalanced pet foods. Symptoms include:
- Bad breath.
- Loss of voice in swine.
- Rough hair coat.
- Muscular atrophy.
- Bone thinning.
- Arched back in swine.
- Irregular heartbeat.
- Heart failure.
- Weight loss.
- Decreased appetite.
- Abdominal pain.
- Vomiting, sometimes with blood.
- Increased thirst.
- Dark-colored feces.
- Excessive urination.
- Reduced egg production.
- Reduced milk production.
- Reduced growth.
The most common use of supplemental vitamin D in livestock is to prevent rickets and other bone deformities. Recent research, however, suggests that this vitamin also has great potential as a substitute for or complement to antibiotics. It can help animals combat a wide array of both bacterial and viral diseases, most notably mastitis. Careful supplementation may also prolong the lives of dogs with congestive heart failure.
Two other interesting uses of vitamin D are enhancing reproductive performance and increasing meat tenderness when fed before slaughter.
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.