Matte, J. J., Guay F. and Girard, C. L. 2006. Folic acid and vitamin B 12 in reproducing sows: New concepts. Can. J. Anim. . In pig nutrition, the present gaps in the information on B-complex vitamins have important implications for empiricism and disparities in dietary recommendations. This is particularly true for folic acid (B 9 ) and vitamin B 12 . Recent studies suggest that the beneficial effects of B 9 on sow prolificacy may be due to enhanced embryo development and survival. Embryo synthesis of estrogens and uterine secretions of prostanoids and cytokines during attachment appear to be key factors in vitamin B 9 regulation of embryo development. Nevertheless, embryo and uterine responses to B 9 are often more pronounced in multiparous sows than in gilts. This parity effect on B 9 responses can be attributed to the metabolic interaction with another vitamin, specifically B 12 . The two vitamins are essential for modulating the transfer of one-carbon groups for protein and DNA synthesis, methylation and gene expression. The metabolic pathway involved is the remethylation of methionine from an intermediary metabolite, homocysteine. A deficiency in B 9 or B 12 may induce a local or systemic accumulation of homocysteine, a powerful pro-oxidant known to impair embryo development. It appears that B 12 status, which is about two times lower in gilts than in multiparous sows, could be a limiting factor for the action of vitamin B 9 on uterus and embryo metabolism during the first pregnancy. Vitamin B 12 status is particularly critical since, in early gestation, the sow uterus drains off a massive amount of B 12 , representing two to three times the B 12 plasma pool. Dietary B 12 , at levels 10 times higher than recommended, have been found to maximize B 12 status and minimize homocysteine accumulation in first parity sows. It appears that an optimum B 9 :B 12 ratio, which has yet to be estimated, would enable vitamin B 9 to have full beneficial effects on sow prolificacy. In the future, it is likely that there will be an even greater need for updated information on the requirements for B-complex vitamins given the "dietary fine tuning" that is necessary for the highly producing pigs that have been selected in recent decades. Des études récentes suggèrent que les effets bénéfiques de la B 9 sur la prolificité de la truie seraient dus à un développement accéléré et à une meilleure survie de l'embryon. La synthèse d'oestrogènes par les embryons ainsi que les sécrétions utérines de prostanoïdes et de cytokines pendant l'implantation apparaissent comme des facteurs déterminant de l'effet régulateur de l'acide folique sur le développement et la survie de l'embryon. Néanmoins, ces effets embryonnaires et utérins de l'acide folique sont souvent plus marqués chez les truies multipares que chez les cochettes. Cet effet de la parité sur la réponse à la B 9 pourrait être attribué à une autre vitamine, la B 12 . Ces deux vitamines interviennent dans le transfert d'unités monocarbonées essentielles à la synthèse de protéine, ...