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. 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 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 minimum levels needed to prevent obvious deficiency. Just one example is the role of vitamin E in the mammary gland health of the dairy cow during late gestation and early lactation.
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. Similar assumptions were made about the essential amino acids, but those assumptions have subsequently proven false. Likewise, studies done in recent years with more highly productive cattle and sheep have shown that performance can be enhanced by supplementation of water-soluble vitamins, most notably niacin and biotin. Most of the other B vitamins have not yet been studied in this manner, and more research remains to be done in this area.
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. Research to date supports the role of vitamins A 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 in 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. 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.
