Context Methionine (Met) is an essential amino acid in pig diets. However, high blood homocysteine concentration, a risk factor for cardiovascular disease, can arise from high dietary Met intake and may indicate an imbalance in the Met cycle. Vitamin B6 acts as a cofactor for enzymes associated with the trans-sulfuration pathway, considered the major elimination route of excess homocysteine. Aims We evaluated the effects of different levels of dietary Met and vitamin B6 supplementation and their interaction with respect to growth performance, blood parameters and metabolic-enzyme gene expression of finishing pigs. Methods Fifty-six crossbred barrows, averaging 75.11 ± 1.84 kg bodyweight (BW), were assigned in a completely randomised block design arranged in a 2 × 4 factorial with two levels of vitamin B6 supplementation (1.58 and 3.58 mg/kg) and four levels of standardised ileal digestible (SID) Met + cystine (Cys) (0.35%, 0.45%, 0.55 and 0.65%), with seven replicates and one animal per pen, for an average duration of 26 days. BW of each pig and quantity of experimental diets on-offer and consumed were recorded at the beginning and end of the experiment. Plasma concentrations of glucose, urea, total proteins, creatinine and triacylglycerol were determined by the colourimetric method, and serum homocysteine by chemiluminescence. Gene expression was measured by quantitative real-time polymerase chain reaction. Key results No interactions (P > 0.05) between vitamin B6 supplementation and SID Met + Cys levels were observed for growth performance, blood parameters or metabolic-enzyme gene expression. Higher vitamin B6 supplementation (3.58 mg/kg) improved (P = 0.05) the feed : growth ratio. Treatments did not affect (P > 0.05) expression of the enzymes methionine synthase or cystathionine γ-lyase, and there was a linear increase (P = 0.01) in serum homocysteine levels with increasing dietary Met + Cys. Increasing vitamin B6 supplementation (3.58 mg/kg) in finishing pig diets increased plasma glucose concentration (P = 0.05), but did not mitigate the increase in homocysteine concentration. Conclusions Overall, a dietary SID Met + Cys intake of 10.46 g/day (corresponding to 0.35%) was sufficient for the growth of finishing barrows from 75 to 100 kg BW. Vitamin B6 supplementation at 3.58 mg/kg improved the feed : growth ratio but was not effective for metabolising the increasing homocysteine concentration via the trans-sulfuration pathway. Implications This study provides much needed empirical data on the dietary SID Met + Cys requirements for finishing pigs, and the metabolism of these amino acids.

中文翻译：

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蛋氨酸+胱氨酸补充维生素B6日粮水平对育肥猪生长性能、血液参数和代谢酶基因表达的影响

背景 蛋氨酸 (Met) 是猪日粮中的必需氨基酸。然而，高血同型半胱氨酸浓度（心血管疾病的危险因素）可能由高膳食 Met 摄入量引起，并可能表明 Met 循环不平衡。维生素 B6 作为与转硫途径相关的酶的辅助因子，被认为是过量同型半胱氨酸的主要消除途径。目的 我们评估了不同水平的日粮 Met 和维生素 B6 补充剂的影响以及它们在育肥猪生长性能、血液参数和代谢酶基因表达方面的相互作用。方法 56 头杂交手推车，平均 75.11 ± 1.84 kg 体重 (BW)，被分配到完全随机区组设计中，按 2 × 4 因子排列，补充维生素 B6 两个水平（1.58 和 3. 58 mg/kg) 和四种标准回肠可消化 (SID) Met + 胱氨酸 (Cys)（0.35%、0.45%、0.55 和 0.65%），每栏 7 个重复和一只动物，平均持续时间为 26 天. 在实验开始和结束时记录每头猪的体重以及提供和消耗的实验日粮的数量。葡萄糖、尿素、总蛋白、肌酐和三酰甘油的血浆浓度通过比色法测定，血清同型半胱氨酸通过化学发光测定。通过定量实时聚合酶链反应测量基因表达。主要结果 在生长性能、血液参数或代谢酶基因表达方面，未观察到维生素 B6 补充剂与 SID Met + Cys 水平之间的相互作用（P > 0.05）。较高的维生素 B6 补充剂 (3.58 毫克/公斤) 改善 (P = 0.05) 饲料：增长率。处理不影响 (P > 0.05) 酶蛋氨酸合酶或胱硫醚 γ-裂解酶的表达，并且血清同型半胱氨酸水平随膳食 Met + Cys 的增加呈线性增加 (P = 0.01)。在育肥猪日粮中增加维生素 B6 补充剂 (3.58 mg/kg) 会增加血浆葡萄糖浓度 (P = 0.05)，但不会减轻同型半胱氨酸浓度的增加。结论 总体而言，10.46 克/天（相当于 0.35%）的日粮 SID Met + Cys 摄入量足以让育肥猪的体重从 75 公斤增长到 100 公斤体重。补充 3.58 mg/kg 的维生素 B6 改善了饲料：生长比，但对通过转硫途径代谢增加的同型半胱氨酸浓度无效。