Cows undergoing a negative energy balance (NEB) often experience a state of immunosuppression and are at greater risk of infectious diseases. The present study aimed to evaluate the impact of a folic acid and vitamin B12 supplement and feed restriction on several immune parameters. Sixteen cows at 45 ± 3 days in milk were assigned to 8 blocks of 2 cows each according to each cow's milk production in the previous week, and within each block, the cows randomly received weekly intramuscular injections of either saline or 320 mg of folic acid and 10 mg of vitamin B12 for 5 weeks. During week 5, the cows were fed 75% of their ad libitum intake for 4 days. Blood samples were taken before the beginning of the experiment, just before feed restriction and after 3 days of feed restriction, in order to evaluate blood cell populations, the phagocytosis capacity and oxidative burst of polymorphonuclear leukocytes (PMNs), the proliferation of peripheral blood mononuclear cells (PBMCs) and concentrations of non-esterified fatty acids (NEFAs) and β-hydroxybutyrate. The vitamin supplement did not affect any of the tested variables except milk fat and lactose content. Feed restriction reduced milk production and increased the concentration of NEFAs. Feed restriction did not affect blood cell populations but did reduce the percentage of PMN positive for oxidative burst after stimulation with phorbol 12-myristate 13-acetate. The proliferation of PBMCs was reduced when the cell culture medium was supplemented with sera collected during the feed restriction. In conclusion, feed restriction affected the functions of PMN and PBMC and this effect was not prevented by the folic acid and vitamin B12 supplement. These results support the hypothesis that the greater risk of infectious diseases in cows experiencing a NEB is related to impaired immune cell functions by high circulating concentration of NEFAs.

中文翻译：

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限制采食以及补充叶酸和维生素B12对奶牛免疫细胞功能和血细胞种群的影响。

处于负能量平衡（NEB）的母牛通常会经历免疫抑制状态，并且感染疾病的风险更大。本研究旨在评估叶酸和维生素B12补充剂和饲料限制对几种免疫参数的影响。根据上一周每头牛的产奶量，将牛奶中45±3天的16头母牛分为8块，每头2头，每头母牛在每个块中随机每周接受肌肉内注射盐水或320 mg叶酸的注射和10毫克的维生素B12，持续5周。在第5周内，为母牛喂食了其75％的自由采食量，为期4天。为了评估血细胞数量，在实验开始前，限制采食前和限制采食3天后采集血样，多形核白细胞（PMN）的吞噬能力和氧化爆发，外周血单核细胞（PBMC）的增殖以及非酯化脂肪酸（NEFA）和β-羟基丁酸酯的浓度。维生素补充剂除了乳脂和乳糖含量外，不影响任何测试变量。饲料限制减少了牛奶的产量并增加了NEFA的浓度。进食限制不影响血细胞数量，但确实降低了佛波醇12-肉豆蔻酸酯13-乙酸酯刺激后氧化爆发的PMN阳性百分比。当向细胞培养基中添加在限制饲喂期间收集的血清时，PBMC的增殖会降低。结论，饲料限制影响了PMN和PBMC的功能，叶酸和维生素B12补充剂并不能阻止这种作用。这些结果支持这样的假说，即由于NEFA的高循环浓度，患有NEB的奶牛感染疾病的更大风险与免疫细胞功能受损有关。