In compound feed, vitamin A (added in the form of retinol/retinyl or beta-carotene precursor) is mainly used to maintain the integrity of the animal's mucosal epithelium (respiratory/intestinal/reproductive tract barrier) and immune defense, ensuring normal reproduction (mating, pregnancy maintenance, embryo development) and the growth, bone differentiation and skin and hair health of the embryo/young age. Deficiency can reduce litter size, weight gain and resilience, and increase the risk of secondary infection. However, the dosage must be controlled as excessive intake can inhibit growth, damage bones and cause teratogenicity (especially in breeding animals, high doses should be used with caution).