Folic acid and vitamin B12 in reproducing sows: New concepts

Abstract

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 (B9) and vitamin B12. Recent studies suggest that the beneficial effects of B9 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 B9 are often more pronounced in multiparous sows than in gilts. This parity effect on B9 responses can be attributed to the metabolic interaction with another vitamin, specifically B12. 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 B9 or B12 may induce a local or systemic accumulation of homocysteine, a powerful pro-oxidant known to impair embryo development. It appears that B12 status, which is about two times lower in gilts than in multiparous sows, could be a limiting factor for the action of vitamin B9 on uterus and embryo metabolism during the first pregnancy. Vitamin B12 status is particularly critical since, in early gestation, the sow uterus drains off a massive amount of B12, representing two to three times the B12 plasma pool. Dietary B12, at levels 10 times higher than recommended, have been found to maximize B12 status and minimize homocysteine accumulation in first parity sows. It appears that an optimum B 9:B12 ratio, which has yet to be estimated, would enable vitamin B9 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.