Physical and chemical properties：
Vitamin A is a yellow flaky crystal with three derivatives of retinol, retinal and retinoic acid; Vitamin A only exists in animal raw materials, and vegetable raw materials contain provitamin A—carotenoids. It can be converted into vitamin A in animals; vitamin A can be stored in large amounts in the liver.
Nutritional physiological function：
The nutrition of vitamin A is related to the functions of the body’s epithelial tissues, vision, reproduction, and nerves. All these functions are maintained by the retinol and retinal in the diet, because these two compounds can be converted into each other in the animal’s body.
① Vision: To maintain the eyesight of animals under low light, vitamin A is a component of rhodopsin, a photosensitive substance in visual cells.
②Epithelial tissue: maintain the health of epithelial tissue; it is related to the synthesis of epithelial mucopolysaccharide secreted by mucus. Lack of vitamin A, dry epithelial tissue and excessive keratinization, susceptible to bacterial infection.
③Reproduction: Participate in the formation of sex hormones and maintain the reproductive ability of pets.
④Bone: It is related to the activity of osteoblasts and maintains the normal development of bones.
⑤ Immunity: Many nutritional deficiencies are related to weakened immune response or slow response to antigens. Vitamin A deficiency causes the most important immune response to protein antigens in mice to be significantly weakened, but the secondary response required for immune memory is not affected much (Ross and Hammerling, 1994). For some viruses, the immune response is weakened when vitamin A is lacking, and the immune response is restored after vitamin A supplementation.
Vitamin A deficiency：
① Can cause night blindness.
② Conjunctivitis, keratitis, dry eye, blindness, pneumonia, tracheitis, enteritis, skin damage, rough coat.
③Slow growth and weight loss.
④ Movement disorders, spasms, convulsions, etc.