Domestic animals provide their vitamin A needs from the vitamin A precursor "carotene" found in plants.

The main provitamin A's are alpha, beta, gamma carotonoids and cryptoxanthines. Not all provitamins show the effect of provitamin A. Xanthophyll gives colour to egg yolk.

Beta (β) - carotene is important in animal nutrition because it is abundant in plants and shows high vitamin activity. Vitamin A activity of beta (β) - carotene is higher than other carotenes.

Plants with very green leaves contain plenty of carotene. The degree of green colour in dried plants indicates the amount of beta (β) - carotene in the feed.

Cats cannot use beta (β) - carotene as vitamin A.

A significant portion of carotene is absorbed in humans, cattle, horses and fish. Absorbed carotene is stored in the liver and fats. This is why body and milk fats are yellow. The body fat of those who cannot absorb carotene is white.

Carotene absorption is different in cattle according to species. Holsteins convert carotene well, so their milk and milk fat are white. Jersey breeds, which absorb carotene in large quantities but cannot utilise it sufficiently, have more yellow milk.

Fats, especially unsaturated fatty acids, accelerate the absorption of carotene. Antioxidant compounds such as vitamin E prevent oxidative degradation of provitamin A and vitamin A in the intestinal villi and intermediate metabolism. In contrast, peroxides formed by the rancidity of fats cause rapid degradation of these compounds.

Insufficiency of protein and phosphorus or high amounts of nitrates in feeds adversely affect the utilisation of carotene in the body.

Carotene is found more in the leaves of plants than in other parts.

The amount of carotene in legumes is higher than in meadow grass. Carotene level in plants decreases after flowering.

During harvesting, drying and storage, most of the carotene in green plants and grasses is destroyed.

Carotene loss is very low in grasses mown at or before flowering and not exposed to excessive sunlight and rainfall.
     Almost all of the carotene is broken down in grasses mown during the seed-bearing period and exposed to sunlight and rainfall.

Feed additives containing calcium and phosphorus mineral mixtures and other trace elements accelerate the breakdown of vitamin A.

Liver is a good source of vitamin A as it accumulates in the form of palmitate in the liver.

Vitamin A absorption decreases in liver disorders.

Vitamin A absorption decreases in liver disorders, pancreatic secretion disorders, bile duct obstructions, mycotoxicosis, coccidiosis and chronic diarrhoea.

Pregnancy significantly affects the plasma vitamin A level.

The plasma vitamin A level decreases during 1/3 of the gestation, then increases and a steep decrease is observed at birth, after which the plasma vitamin A level rapidly normalises.

The placenta prevents the passage of vitamin A and carotenes to the offspring; the vitamin A level of the offspring remains significantly lower than the vitamin A level of the mother.

Colostrum is an important source of vitamin A for the foal.

When the amount of vitamin A in the feed is reduced, the body tries to replenish it from liver stores.

Retinol and carotenes are absorbed from the small intestine.

They are stored in the liver in the cuppiferous cells. vitamin A is stored as palmitate. In cells, vitamin A is usually stored in the endoplasmic reticulum (ER) and Golgi.

Vitamin A circulates by binding to proteins.

Since retinol binding protein (RBP) decreases in protein deficiencies, the concentration of vitamin A in plasma decreases even when sufficient vitamin A is present.
     In this case, treatment and nutrition should be applied to eliminate protein deficiency.

Vitamin A plays important roles in vision, growth, epithelialisation, growth, bone development, reproduction and embryo development.

Vitamin A affects spermatogenesis and thus fertility in all species.

Vitamin A has a positive effect on functions such as favourable development in the number and ratio of T and B lymphocytes, increase in the phagocytosis ability of peritoneal macrophages, development of immunoglobulin synthesising functions of plasma cells.

In vitamin A deficiencies, vitamin D synthesis in the liver is impaired.

Vitamin A has an indirect immunostimulatory effect by eliminating the immunosuppressive effect of corticosteroids on the immune system.

Kidney disorders, oestrus cycle irregularities, placental underdevelopment and reproductive disorders, foetal resorption, congenital disorders are the disorders seen in vitamin A deficiency.

Vitamin A deficiency causes night blindness. Night blindness may lead to blindness.

Vitamin A deficiency in dairy cattle;

Throwing offspring, weak vitality, muscle weakness, convulsions, staggering gait, weakening, drying and shedding of the skin around the neck, tail tip and nape, oedema are observed.

Vitamin deficiency leads to infertility in breeding animals, abortion in pregnant animals, and birth of dead, weak or blind offspring.  In milder cases, the offspring are born with vitamin A depots.

Vitamin A deficiency in beef cattle;

In male breeders, sexual activity decreases significantly due to results such as degenerations in sperm epithelium, decrease in sperm count and mobility, increase in abnormal sperm count.

Vitamin A deficiency in sheep;

Night blindness, dead or weak labour, muscle spasms and convulsions are observed. The frequency of formation of stones in the urinary tract increases.

Vitamin A deficiency in horses;

Night blindness, tear discharge, keratinisation of the cornea, respiratory system disorders, poor development of hooves, progressive weakening and loss of appetite.

Vitamin A deficiency in poultry;

The first symptoms of vitamin A deficiency in poultry fed insufficient in terms of vitamin A are stagnation in growth, weakening, fluffy feathers and wobbly gait.  In adult animals, egg production and hatching rate decrease. Inadequate growth, increased susceptibility to diseases, muscle imbalance, mixed feathering, decreased gland secretions, damage to the epithelium of the mouth and respiratory tract, accumulation of urate crystals in the kidneys.

Adult birds have typical eye lesions characterised by the collection of cheesy exudate around the eye which can cause the head to enlarge; this condition is known as feeding catarrh.