Optimum nutrition occurs only when the animal body makes efficient use of the nutrients in the feed for growth, health, reproduction and survival. Whereas all nutrients, including proteins, fats, carbohydrates, vitamins, minerals and water, are essential for these vital functions, vitamins have an added dimension—they are required in adequate amounts to enable the animal to efficiently utilize the other nutrients in the feed.
Moreover, the minimal amounts of vitamins and other nutrients that are sufficient for adequate growth or survival are not necessarily enough for optimum performance in animals under commercial production conditions. Research increasingly indicates that vitamin requirements for growth are less than those for the immune system. Feedstuffs often do not provide sufficient amounts of vitamins needed to prevent deficiencies or allow optimum performance. Vitamin nutrition is a dynamic input for the production and marketing of meat, milk and eggs, but it must be evaluated and updated regularly to accommodate improvement in animal production efficiency, enhancement of feed processing and storage methods, changes in conditions on the farm, improvements in the quality of food products produced by animals, and new vitamin nutrition knowledge. For companion animals, an additional consideration is vitamin requirements in relation to aging. Unlike food-producing animals, pets are fed to advanced years relative to their life spans.
Conversion of swine and poultry operations into complete confinement without access to vitamin-rich pasture has had a profound effect on vitamin nutrition (as well as mineral nutrition). Modern ruminant and horse operators likewise have decreased the quantity and quality of pasture provided to many classes of livestock. The husbandry practice of confinement rearing has put added stress (e.g., crowding and exposure to disease organisms) on poultry and livestock production systems.
Stress increased by confinement may impair the ability of ruminants to synthesize or utilize some vitamins. Confinement rearing in dairy cattle operations as well as in beef cattle and lamb finishing operations has dramatically affected vitamin nutrition. In confinement rearing, milking cows and feedlot animals receive higher concentrate diets, thus eliminating their access to pasture and other green roughages rich in vitamins (particularly vitamins A and E).
Higher production rates mean a greater loss of vitamins through the resulting products (e.g., milk and meat). Better feed efficiencies of higher producing animals increase their vitamin requirements. An additional problem with confinement rearing is that group feeding in restricted areas affects individual animals' consumption of vitamins and other nutrients. Competition among animals of different sizes, ages and breeds may significantly alter the daily intake of an individual animal, resulting in excess intake by more aggressive animals and inadequate intake by less aggressive animals.
During the last 25 years, ruminant diets have changed to include not only higher levels of low-vitamin grains but also increased use of nonprotein nitrogen sources such as urea. Protein supplements, such as soybean meal and cottonseed, do provide some vitamins; however, high concentrate diets fed to high-producing dairy cows and feedlot animals can contain urea, which provides only a source of nitrogen and no vitamins. During this same time, the trend in dairy cattle has been toward feeding complete diets containing both grain and forage to all milking animals. This group feeding system does not allow for individual differences in vitamin and other nutrient requirements.
To meet the increased vitamin needs of livestock resulting from feed formulation changes and advancements in production rates, the number of vitamins supplemented and the numerical values of the requirements have changed. For example, ruminant diets previously never contained niacin and thiamin. Likewise, requirements for vitamins A, D and E have increased in recent years. Early NRC species requirement publications starting in the 1940s and 1950s included margins of safety to compensate for vitamin losses during feed processing and storage and for other factors influencing the vitamin needs of commercially produced livestock (so-called influencing factors). As an example, the 1944 NRC for poultry allowed a general 20% safety margin for all vitamins. Later, however, it was recognized that the influencing factors varied considerably from farm to farm. Thus, in later NRC publications, the margins of safety were excluded, and the NRC vitamin requirements were reduced to minimum values. This gave the nutritionist the flexibility to use these minimum requirement values as a base, arrive at margins of safety and adjust vitamin allowances to compensate for the influencing factors occurring in individual operations.
Dietary vitamin fortification is not only cost-effective, but vital to efficiency for all stages of animal production. Vitamins are micro-ingredients with macro-responsibility—their involvement in growth, health, reproduction and survival of livestock is extremely important, relative to their weight and cost in the finished feed. Vitamins are the least costly components of animal diets and represent only a minute fraction of animal feed, amounting to less than 1% to 2% of the feed cost and 0.1% by weight (Figure 1). Even in dairy cattle diets, which would result in the greatest amounts of supplemental vitamins consumed due to the higher feed intakes, vitamin fortification typically costs less than 10 cents per animal per day (Erdman, 1992).
