Centre de recherche et développement de Sherbrooke, Agriculture et agroalimentaire Canada, 2000 rue Collège, Sherbrooke, Québec J1M 0C8, Canada.
Centre de recherche et développement de Sherbrooke, Agriculture et agroalimentaire Canada, 2000 rue Collège, Sherbrooke, Québec J1M 0C8, Canada.
Animal. 2023 Jul;17 Suppl 3:100834. doi: 10.1016/j.animal.2023.100834. Epub 2023 Apr 28.
Synthesis of B vitamins by the rumen microbiota is usually sufficient to avoid the appearance of clinical deficiency symptoms in dairy cows under normal feeding conditions. Nevertheless, it is now generally accepted that vitamin deficiency is much more than the appearance of major functional and morphological symptoms. Subclinical deficiency, which is present as soon as the supply is lower than the need, causes cellular metabolic changes leading to a loss of metabolic efficiency. Folates and cobalamin, two B vitamins, share close metabolic relationships. Folates act as co-substrates in one-carbon metabolism, providing one-carbon unit for DNA synthesis and de novo synthesis of methyl groups for the methylation cycle. Cobalamin acts as a coenzyme for reactions in the metabolism of amino acids, odd-numbered chain fatty acids including propionate and de novo synthesis of methyl groups. Both vitamins are involved in reactions to support lipid and protein metabolism, nucleotide synthesis, methylation reactions and possibly, maintenance of redox status. Over the last decades, several studies have reported the beneficial effects of folic acid and vitamin B supplements on lactation performance of dairy cows. These observations indicate that, even when cows are fed diets adequately balanced for energy and major nutrients, B-vitamin subclinical deficiency could be present. This condition reduces casein synthesis in the mammary gland and milk and milk component yields. Folic acid and vitamin B supplements, especially when given together, may alter energy partitioning in dairy cows during early and mid-lactation as indicated by increased milk, energy-corrected milk, or milk component yields without affecting DM intake and BW or even with reductions in BW or body condition loss. Folate and cobalamin subclinical deficiency interferes with efficiency of gluconeogenesis and fatty acid oxidation and possibly alters responses to oxidative conditions. The present review aims to describe the metabolic pathways affected by folate and cobalamin supply and the consequences of a suboptimal supply on metabolic efficiency. The state of knowledge on the estimation of folate and cobalamin supply is also briefly mentioned.
反刍动物微生物群可以合成维生素 B 以满足通常的需要，从而避免在正常饲养条件下奶牛出现临床缺乏症状。然而，人们现在普遍认为，维生素缺乏不仅仅是出现主要功能和形态症状。亚临床缺乏是指一旦供应低于需求，就会出现细胞代谢变化，导致代谢效率丧失。叶酸和钴胺素是两种 B 族维生素，它们的代谢关系密切。叶酸作为一碳代谢的辅酶，为 DNA 合成和从头合成甲基供体提供一碳单位，用于甲基化循环。钴胺素作为氨基酸代谢、奇数链脂肪酸（包括丙酸）和从头合成甲基的反应的辅酶。这两种维生素都参与支持脂质和蛋白质代谢、核苷酸合成、甲基化反应以及可能的氧化还原状态维持的反应。在过去几十年中，已有多项研究报道了叶酸和维生素 B 补充剂对奶牛泌乳性能的有益影响。这些观察结果表明，即使奶牛的日粮能量和主要营养素平衡充足，也可能存在 B 族维生素亚临床缺乏。这种情况会降低乳腺和牛奶中的酪蛋白合成以及牛奶和牛奶成分的产量。叶酸和维生素 B 补充剂，特别是同时给予时，可能会改变奶牛泌乳早期和中期的能量分配，表现为产奶量、校正奶能量或牛奶成分产量增加，而不影响干物质采食量和体重，甚至在体重或体况下降的情况下也会增加。叶酸和钴胺素亚临床缺乏会干扰糖异生和脂肪酸氧化的效率，并可能改变对氧化条件的反应。本综述旨在描述叶酸和钴胺素供应对代谢途径的影响以及供应不足对代谢效率的影响。还简要提到了对叶酸和钴胺素供应估计的知识状态。
