Vitamin A, so called retinol, is the major element for animal vision, immune function, and skin health. Retinol will be converted to retinal, which forms the necessary rhodopsin to support normal night vision in the visual process. Additionally, vitamin A is vital for animal growth, bone development, and reproductive capacity; it enhances the immune system, improving overall disease resistance in animals. Its impact on cellular function is profound, involving the regulation of carbohydrate, fat, and protein metabolism. Animal-based foods such as fish liver oil, whole milk, and fish meal are its primary sources. Plant-based materials contain precursors like beta-carotene, found in green plants such as grass, clover, alfalfa, and carrots. Ruminants, for instance, can effectively convert beta-carotene into vitamin A as cats need to obtain vitamin A directly from their diet.

Vitamin D is the primarily sourced from whole milk, liver oils, and sun-dried green fodder. Vitamins D2 and D3 are the two most important forms; the former is derived from ergosterol in plants transformed by sunlight, while the latter is produced in animals from 7-dehydrocholesterol under ultraviolet light. Vitamin D helps regulate calcium and phosphorus absorption, excretion, and bone mineralization, particularly crucial when calcium and phosphorus supply is insufficient or improperly balanced. Vitamin D deficiency can lead to calcium and phosphorus metabolism disorders, resulting in issues such as rickets, osteoporosis, skeletal and joint deformities, growth disorders, brittle bones, and inadequate eggshell strength.

Vitamin E, especially d-α-tocopherol, is of great importance in animal nutrition and possesses high biological activity. Young green forages and wheat seedlings have a high content of tocopherols whereas grains have a low content of α-tocopherol, resulting in lower vitamin E activity. Root crops and low-fat feeds such as skim milk and whey contain little tocopherols. Consequently, the more stable dl-α-tocopheryl acetate is often used in animal nutrition as a substitute for the easily oxidized d-α-tocopherol. Vitamin E is essential for cellular metabolism, acting as an antioxidant to protect unsaturated fatty acids and vitamin A from oxidation, regulating muscle and carbohydrate metabolism, reproductive health, and hormonal balance. Vitamin E deficiency can lead to problems in livestock such as muscle atrophy, heart disease, and reduced reproductive capacity, significantly affecting health and productive performance.

Vitamin C (ascorbic acid) is a potent reducing agent and highly unstable in aqueous solutions, especially when exposed to heat, light, and oxygen. Furthermore, the presence of trace heavy metals and alkaline substances can elevate its degradation. Mono C has better stability, but remain highly sensitive to heat that may limit their effectiveness in feed processing. Among all Vitamin C formulations, Sodium Ascorbyl Phosphate, particularly monophosphates, provide the best bioavailability and stability, making them the preferred choice for feed additives. This formulation protects both Vitamin C from degradation and expands its scope of applications in animal nutrition.

Vitamin B2 functions as a coenzyme in reactions involving numerous oxidoreductases, collectively known as flavoproteins, which are key elements for the transfer of hydrogen atoms. Thus, like other Vitamin B complex, Vitamin B2 acts as a coenzyme in the metabolism of proteins, fats, and nucleic acids. It also participates in the visual process. Animal feeds, especially dairy products such as whey powder and skimmed milk powder, are rich in Vitamin B2. Alfalfa meal and feed yeast are also good sources of Vitamin B2. Grains, milling by-products, root crops, and plant protein feeds contain lower levels of Vitamin B2. Vitamin B2 deficiency can lead to growth retardation, poor feed utilization, and diarrhea. In chickens, it results in the characteristic symptom of curved toes.

Pantothenic acid is an essential nutrient found in most feed ingredients, with the exception of cassava. Sources of poverty include root crops, barley and corn; rich sources include dairy products, fish-soluble pulp, by-products of flour, high quality alfalfa powder, beer and yeast, oil meal and plant protein products. Pantothenic acid is a component of coenzyme A, taking part in protein, carbohydrate, and fat metabolism. Deficiency of pantothenic acid can lead to depigmentation, hair/feather loss, ulcer, diarrhea, fatty liver, loss of appetite, reproductive problems, insufficient milk supply, convulsions, paralysis, and increased stress sensitivity. The natural pantothenic acid content in modern feed ingredients is insufficient, requiring supplementation for pigs and poultry; ruminants generally do not need supplementation, but calves do. D-calcium Pantothenate is easily absorbed and can function as a source of pantothenic acid in metabolism, and only D-form is biological active. 1 mg of calcium D-pantothenate equals 0.92 mg of pantothenic acid; 1 mg of pantothenic acid equals 1.087 mg of calcium D-pantothenate.

All feed ingredients, except cassava, contain folic acid, mostly in bound forms but with good bioavailability. Beer and feed yeast are particularly rich in folic acid, with other good sources including green parts of plants, soybean meal, potatoes, wheat bran, and liver. Grains and fish meal contain lower amounts. The active form of folic acid functions as a coenzyme in metabolism, transferring one-carbon units (such as formyl and methyl groups), particularly in amino acid and nucleic acid synthesis. It works together with Vitamin B12 and is core for the formation of red and white blood cells. Folic acid deficiency can lead to anemia, especially pronounced when Vitamin B12 is also deficient, and may cause growth retardation, diarrhea, and reproductive disorders. In poultry, poor feather quality, feather discoloration, leg injuries, and reduced egg production may occur, and hair loss in pigs. Animals can synthesize folic acid through gastrointestinal microbes, but this is usually insufficient for poultry and young animals, necessitating supplementation. Using folic acid antagonists (such as sulfonamides) need special attention to supplementation, and it is generally not required in adult ruminants.

Niacin is found in all plant and animal feed ingredients; rich sources include dry feed yeast, wheat bran, peanut meal, sunflower meal and fish pulp, while poor sources include dairy products, cassava, soybean and flaxseed meal, oats, rye and corn. Pigs and poultry have a low capacity to utilize nicotinic acid from grain and milling by-products. Mammals can synthesize nicotinic acid to a limited extent from tryptophan; pigs require about 50-60 mg of tryptophan to produce 1 mg of nicotinic acid. Niacin and nicotinamide are components of the coenzymes NAD and NADP, involving in the synthesis and breakdown of carbohydrates, fats and proteins. Niacin deficiency will interfere with glycolysis, the citric acid cycle, respiratory chain, and fat synthesis. Its symptoms include skin abnormalities, gastrointestinal disorders, growth retardation, feather development problems, decreased egg production, mucosal inflammation and ulceration, and joint changes. In dogs, the typical symptom is black tongue disease. High doses of nicotinic acid can cause vasodilation. In rats, the LD50 is 7 grams per kilogram of the body weight.