The periparturient period is the period from three weeks before calving to three weeks post-calving. This period is important in terms of health, productivity and profitability, and is fundamental to successful lactation. During this period, the animal experiences stress because of hormonal changes due to pregnancy and the significant rise in milk production. In addition, a negative energy balance usually occurs, because the demand for nutrients to sustain milk production increases by more than the nutrient supply during the periparturient period. The immunity of dairy cattle is suppressed around parturition, which increases their susceptibility to infections. Special care regarding nutrition can reduce the risks of metabolism and immunity depression, which dairy cattle face during the periparturient span. Folic acid is relevant in this regard because of its critical role in the metabolism to maintain lactational performance and to improve health. Being a donor of one-carbon units, folic acid has a vital role in DNA and RNA biosynthesis. Generally, the folic acid requirements of dairy cattle can be met by the microbial synthesis in the rumen; however, in special cases, such as during the periparturient period, the requirement for this vitamin strictly increases. Vitamin B12 also has a critical role in the metabolism as a coenzyme of the enzyme methionine synthase for the transfer of a methyl group from folic acid to homocysteine for the regeneration of methionine. In the current review, we highlight the issues facing periparturient dairy cattle, and relevant knowledge and practices, and point out future research directions for utilization of the associated vitamins in ruminants, especially during the periparturient period.

中文翻译：

---

围产期奶牛单独或与维生素B12补充叶酸的概述。

围产期是从产犊前三周到产后三周的时期。这个时期对健康，生产力和盈利能力都非常重要，并且是成功哺乳的基础。在此期间，由于怀孕引起的荷尔蒙变化和牛奶产量的显着增加，动物会承受压力。另外，通常会出现负能量平衡，因为在围产期，对维持奶产量的养分需求的增加量要大于养分供应量的增加。产奶前后乳牛的免疫力受到抑制，这增加了它们对感染的敏感性。营养方面的特别护理可以减少产奶期围产期面临的新陈代谢和免疫力降低的风险。叶酸在这方面是相关的，因为它在代谢中维持乳汁功能和改善健康的关键作用。叶酸是一碳单元的供体，在DNA和RNA的生物合成中起着至关重要的作用。通常，通过瘤胃中的微生物合成可以满足奶牛的叶酸需求。但是，在特殊情况下，例如围产期，对这种维生素的需求会严格增加。维生素B12在代谢中也起着至关重要的作用，它是蛋氨酸合酶的辅酶，用于将甲基从叶酸转移到高半胱氨酸以再生蛋氨酸。在当前的评论中，我们重点介绍围产期奶牛面临的问题以及相关的知识和做法，