Vitamin nutrition remains a challenging and dynamic field for ruminant nutritionists. As with other aspects of nutrition, vitamin status is affected by rumen fermentation as well as diet composition. National Research Council (NRC) publications for ruminants are dairy cattle (NRC, 2001), Beef Cattle (NRC, 2000), Sheep (NRC, 1985) Goats (NRC, 1981); and Small Ruminants (NRC, 2007b). These publications define vitamin requirements only for vitamins A, D and E. The current NRC requirements for these vitamins are based on data that are at least 30 years old and, in some cases, greater than 50 years old (Weiss, 1998). The fat-soluble vitamins have long been recognized as essential in the ruminant diet; however, the determination of optimal levels of vitamins A, D and especially vitamin E in ruminants has required a significant research effort. Today it is clear that in a number of situations, the dietary levels of vitamins A, D and E necessary to optimize productivity are greater than the NRC’s minimum levels needed to prevent obvious deficiency.
Many factors in feeds are destructive to vitamins A, D and E (e.g., trace minerals, choline, unsaturated fat, heat, oxygen, light, moisture, etc.). Vitamin concentrations of vitamins A, D and E are lost by pelleting (heat, pressure, moisture and friction) and as a result of storage. Greater amounts of vitamin E are needed to prevent mastitis in dairy cattle and to ensure meat quality (i.e., to provide greater stability of tissues and to control lipid oxidation in beef). High levels of vitamin D prior to slaughter have been shown to be a cost-effective means of improving beef tenderness. Vitamin A deficiency is often seen in heavily parasitized animals that supposedly were receiving an adequate amount of the vitamin. Mycotoxins are known to cause digestive disturbances, such as vomiting and diarrhea, as well as internal bleeding. These conditions interfere with absorption of dietary vitamins A, D, E and K. Level of fat in the diet may affect absorption of the fat-soluble vitamins A, D, E and K, as well as the requirement for vitamin E and possibly other vitamins. Fat-soluble vitamins may fail to be absorbed if digestion of fat is impaired. High costs of fat as an energy source can result in minimizing dietary fat in current, least-cost diet formulations, thus potentially reducing absorption of fat-soluble vitamins (Hoffmann-La Roche, 1979).
Intensified production for improved weight gains, feed efficiency, milk production or reproductive performance can increase the metabolic demand for many vitamins. Intensified production also elevates stress through confinement, overcrowding and competition of animals for feed and water. The added stress increases the susceptibility of animals to various diseases. Moving ruminant livestock operations into complete confinement without access to pasture has had a profound effect on vitamin nutrition (as well as mineral nutrition). Previously, pasture or range rearing could be depended upon to provide significant quantities of most vitamins. Young, lush, green grasses or legumes are good vitamin sources. More available forms of vitamins A and E are present in pastures, with green forages containing ample quantities of beta-carotene and alpha-tocopherol versus lower bioavailable forms in grains. Likewise, while on pasture, grazing animals were receiving adequate vitamin D from irradiation of skin by ultraviolet light (UV). Confinement rearing requires producers to pay more attention to higher vitamin requirements needed for this management system.
Synthesis of the water-soluble vitamins by the rumen microbial population was demonstrated during the 1930s, ’40s and ’50s, and corresponding deficiencies were produced in preruminant calves and lambs. This early research led to the assumption that any animal with a functional rumen has no absolute requirement for water-soluble vitamins. It is well known that microorganisms in the rumen synthesize most B-vitamins (no synthesis of choline) and vitamin K. The ability to synthesize B-vitamins and vitamin K in the young ruminant develops rapidly when solid feed is introduced into the diet. The rumen contents subsequently pass through parts of the digestive tract that are ideally suited for digestion and absorption of microbial products. Consequently, B-vitamins and vitamin K synthesized in the rumen are readily available to the animal.
Studies done in recent years with more highly productive cattle and sheep have shown that performance can be enhanced by supplementation of vitamins other than just A, D, and E. Although rumen microorganisms normally synthesize B-vitamins and vitamin K in sufficient quantities to meet requirements, under special circumstances deficiencies have occurred and hence supplementation has proven beneficial for thiamin, niacin, vitamin B12, choline, biotin, and vitamin K. Vitamin C can be synthesized in tissues by ruminants and most other animals under normal conditions. However, clinical cases of scurvy in ruminants have been described and supplemental vitamin C may be beneficial under certain conditions (e.g., stress).
Digestive systems of young ruminants, before full development of the rumen and its microflora, resemble those of monogastric animals. A reasonable assumption is that ruminants, at the tissue level, require the same vitamins as monogastric animals. Similarity of requirements has been shown for the young ruminant before development of the rumen (usually 6-8 weeks of age). Additional B-vitamin supplementation to veal calves was found to improve measurements of calf health to week nine, but did not improve health parameters from weeks 10 through 23 (Woodet al., 2007). Deficiencies of thiamin, riboflavin, vitamin B6, pantothenic acid, choline, biotin, niacin and vitamin B12have all been produced experimentally in young ruminants prior to the development of the rumen (Miller, 1979).
One of the primary factors affecting vitamin requirements in livestock is the level of physiologic stress, which will vary with the level or rate of production; the type and density of housing; prevailing environmental quality factors (such as temperature changes, humidity and air quality); the level of disease exposure; and the quality and consistency of human management of livestock. Stress and the release of related hormones leads to immune suppression and reduced productivity in livestock. Most of the vitamins are required for normal immune function and can enhance immunity under certain circumstances. Requirements that are based on measures of immune function are usually higher than those that are based on production or reproduction (Weiss, 1998). Research to date supports the role of vitamins A, D, and E in maintaining the ruminant immune system, and data are becoming available on other vitamins. With the trend toward confinement production systems, the role of vitamins and the immune system should remain a strong interest for the future.
Trends in ruminant vitamin nutrition today include the increased supplementation of vitamin E under certain conditions, including the time near parturition in dairy and beef cows, during the preweaning and immediate postweaning period in calves and lambs, and during the receiving and feeding periods for beef cattle in feedlots. Similarly, the use of supplemental water-soluble vitamins in ruminants is increasing where supported by research. Supplemental niacin is used as an aid in metabolism in high-producing dairy cows in the latter part of the dry period and in early lactation. Supplemental thiamin may be required to counteract thiamin antagonists and for prevention of polioencephalomalacia for ruminants consuming high-concentrate diets. Choline supplementation has recently proven beneficial to dairy cattle in milk production when provided as a rumen protected product. More recently, supplemental biotin is being added to the rations of dairy cattle for enhanced hoof integrity as well as increased milk production, via its effects on hoof horn production and as a cofactor for several important metabolic enzymes.
Carnitine, a vitamin-like substance has recently been shown as a valuable supplement to transitional dairy cows. It is being used as an approach to prevent fatty liver in periparturient dairy cows. In the 2000 edition of “Vitamin Nutrition Compendium,” carnitine was discussed for various species, but not for ruminants. There is now an awareness of the nutritional need of ruminants for carnitine. Therefore in the current “Vitamin Nutrition Compendium” there is a section dealing with carnitine for ruminants.