B-COMPLEX VITAMINS FOR DAIRY-COWS - A NEW APPROACH

It is generally accepted that ruminant requirements for B-complex vita mins are fulfilled by the synthesis of these vitamins by ruminal micro flora. Most of the studies on this topic were conducted during 1940-19 50. These works demonstrated that, even when ruminants are fed a B-com plex vitamin-free diet, the synthesis of these vitamins by the ruminal microflora was sufficient to avoid deficiency symptoms if the rumen i s well-developed and functional. These works led to the conclusion tha t dairy cow requirements for B-complex vitamins are the minimal quanti ty to be fed to avoid deficiency symptoms. However, in a context of ma ximisation of the effects of nutrition on dairy cow health and perform ances, the criteria used to define the requirements need to reviewed. As for the major nutrients, requirements for B-complex vitamins need t o be studied, not on the point of view of deficiency, but rather in re lation with an optimisation of cow health, performances and the qualit y of the product. Only some of the B-complex vitamins, biotin, nicotin ic acid, folic acid and vitamin B-12, have been studied in that purpos e, they will be discussed in the present talk.