B-complex vitamins for dairy cows: A new approach

It is generally accepted that ruminant requirements for B-complex vitamins are fulfilled by the synthesis of these vitamins by ruminal microflora. Most of the studies on this topic were conducted during 1940-1950. These works demonstrated that, even when ruminants are fed a B-complex vitamin-free diet, the synthesis of these vitamins by the ruminal microflora was sufficient to avoid deficiency symptoms if the rumen is well-developed and functional. These works led to the conclusion that dairy cow requirements for B-complex vitamins are the minimal quantity to be fed to avoid deficiency symptoms. However, in a context of maximisation of the effects of nutrition on dairy cow health and performances, the criteria used to define the requirements need to reviewed. As for the major nutrients, requirements for B-complex vitamins need to be studied, not on the point of view of deficiency, but rather in relation with an optimisation of cow health, performances and the quality of the product. Only some of the B-complex vitamins, biotin, nicotinic acid, folic acid and vitamin B-12, have been studied in that purpose, they will be discussed in the present talk.