Twenty-four multiparous and 16 primiparous dairy cows were assigned by parity, BW, and milk production to 20 blocks of 2 cows each. Within each block, the cows were injected weekly with either 0 or 160 mg of folic acid from 45 d after mating to 6 wk after parturition. Supplementary folic acid augmented the placental and colostral transfer of folates to the calf but had no effect on blood hemoglobin, birth weight, or growth and feed intake of the calf during the first 10 wk of life. The supplemental folic acid increased serum folates but had no marked effect on blood hemoglobin and BW of cows. Supplementary folic acid tended to increase milk folates, milk production, and the percentage of milk protein during the last half of the lactation curve but had no effect on milk folates and milk production during the first 6 wk after parturition when the injections of folic acid increased the percentage of milk protein in multiparous cows but had no effect on primiparous cows. The supply of folates by the diet and the synthesis by ruminal microflora is sufficient to prevent folic acid deficiency in dairy cows and to maintain normal gestation and lactation, but not to achieve maximal production of milk and protein in multiparous dairy cows during gestation and lactation.

Three groups of 34 gilts received, from 9 wk of age until slaughter at 7 wk of gestation, diets supplemented with either 0, 5, or 15 mg/kg of folic acid. The concentration of serum folates increased linearly (P < or = .05) with the level of added folic acid. Although the growth performance was not influenced by the treatments during the overall growing period, feed intake (P < or = .10) and body weight gain (P < or = .05) from 17 to 21 wk of age increased linearly as folic acid level in the diet increased. Age and body weight at puberty as well as body weight gain during gestation were not influenced (P > or = .32) by treatments. Dietary folic acid addition did not affect (P > or = .21) either total weight and empty weight of uterine horns or ovarian total weight, stroma weight, and number and weights of corpora lutea. No treatment effect (P > or = .35) was observed on placental surface, number of placental areolae, litter size, fetus weight, or total litter weight or on fetal DNA, RNA, and protein. However, the concentration of folates in fetuses increased linearly (P < or = .03) with the addition of folic acid in the dam's diet. In conclusion, although a dietary addition of as high as 15 mg/kg of folic acid seemed to influence growth performance of gilts by the end of the growing period, it did not affect age at puberty.(ABSTRACT TRUNCATED AT 250 WORDS)

Girard, C. L. and Matte, J. J. 2006. Impact of B-vitamin supply on major metabolic pathways of lactating dairy cows. Can. J. Anim. Sci. 86: 213-220. Knowledge of the major nutrient requirements of dairy cows has increased substantially during the past decades. Little is known, however, about the importance of the roles played by B vitamins. Since most of those vitamins act as essential cofactors in energy, protein and lipid metabolism, it is likely that as milk yield increases, the demand for these cofactors also increases. The supply of B vitamins from dietary sources and synthesis by the ruminal microflora is generally sufficient to avoid deficiency symptoms, but could be insufficient for optimizing metabolic efficiency, production, composition and the nutritional quality of milk in high-producing dairy cows. Results from recent experiments show how the supply of three B vitaminsfolic acid, biotin and vitamin B 12 -affects major metabolic pathways. Supplementary biotin has frequently been reported to increase milk yield but has a limited effect on milk composition. Folic acid supplements have been found to increase milk and milk protein yields in multiparous cows without affecting dry matter intake when vitamin B 12 supply was adequate. An insufficient vitamin B 12 supply blocked those effects but they can be restored through vitamin B 12 supplementation. Supplemental vitamin B 12 and biotin increased milk and milk protein yields without changing dry matter intake. Vitamin B 12 utilization by tissues increased in cows fed supplementary folic acid simultaneously; plasma glucose also increased in these cows but plasma biotin decreased. From these findings, it appears that, in high-producing dairy cows, especially in early lactation, the strong competition for nutrients that occurs between gluconeogenesis, methylneogenesis and protein synthesis increases the amount of folic acid, vitamin B 12 and biotin required to maintain metabolic efficiency, especially when the nutrient supply is limited. These observations emphasize the need to review the paradigm according to which B-vitamin supply by ruminal microflora cannot be limiting in dairy cow. Les connaissances sur les besoins des vaches laitières en nutriments majeurs ont augmentées substantiellement au cours des dernières décennies. Cependant, on connaît encore peu l'importance des rôles des vitamines B. La plupart de ces vitamines sont des cofacteurs essentiels dans les métabolismes énergétiques, protéiques et lipidiques, il est donc probable que la demande pour ces cofacteurs augmente avec la production laitière. Les apports en vitamines B provenant de l'alimentation et de la synthèse par la microflore du rumen suffisent généralement à éviter les symptômes de déficience mais sans nécessairement permettre d'optimiser l'efficacité métabolique, la production, la composition et la qualité nutritionnelle du lait chez les vaches hautes productrices. Les résultats d'expériences récentes mettent en évidence l'impact sur les voies métaboliques majeures des apports en tr...

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15 after mating. one uterine horn was used to collect conceptuses and uterine *flushings" for hormonal and metabolite determinations; conceptuses from the other hom were enzymatically dispersed and placed in cell culture with and without dehydroepiandrosterone (DHEA). The decrease.in serum folates was attenuated (P < 0'06) and the total and saturated folate binding capacities in early gestation wereincreased 1F. o.orl in sows receiving additional dietary folicacid rhe volume of uterine flushings recovered was greater (p < 0.02) on auy ts t'* on day12, as wa-s its content of protein (p < 0.06). In sows receiving the dietary .uppt"..ni oFfolic acid, total uterine prostaglandin iitc;nr.*u. three times higher on day l2 and two times higher on day I 5 (p < 0.04) than for sows fed ihe experim.titui aiJ, without supp'lement; although numerically substantial (60% higher)' the effect was not significant for pGFro (p > 0.16). conceptus homogenates coniained more folic acid (P < 0 02) and DNA (P < 0.000 I ) on day l5 than on day l2.Their total protein content, in sowJ slaughtered on day 12 of gestation, tended (P < 0'07) to be higher in supplemented,t-in unrupplemented uni.nuir.