ABSTRACT This study investigated the effects of low-protein diet supplemented with Lysine (Lys), Methionine (Met), Threonine (Thr), and Tryptophan (Trp) on small intestine morphology, enzyme activity, blood urea nitrogen, and gut microbiota and metabolites in weaned piglets. Eighteen weaned pigs weighing an average of 9.57 kg received one of three treatments: a normal protein diet with 20% crude protein (CP, diet [NP]), a moderately reduced protein diet with 17% CP (MP), or a low-protein diet with 14% CP (LP). All three diets were supplemented with Lys, Met, Thr and Trp to meet essential amino acid requirements for post-weaned piglets according to the NRC (2012). Following a 45 d study period, piglets on the LP and MP diets demonstrated atrophic small intestinal morphology, with decreased villus heights and lower ratios of villus height to crypt depth (p < 0.05); pepsin activity in the stomach was also reduced in these two groups (p < 0.05). Increased plasma cholesterol and decreased blood urea nitrogen presented in the MP and LP groups compared with the NP group (p < 0.05). Overall, gastrointestinal hormones were not affected by dietary protein levels with the exception of reduced somatostatin levels in the MP and LP groups. Jejunum and colon microbiota were not affected at either the phyla or genera level in any of the diets. Colonic ammonia nitrogen concentration was reduced in MP and LP groups. Dietary protein level had no effect on short chain fatty acids or biogenic amines. Our data suggest that reducing dietary protein levels by 3% (MP) or 6% (LP) in weaned pigs has the potential to decrease nitrogen emissions and impaired digestive capacity. Therefore, dietary protein level cannot be reduced by more than 3% in consideration of maladaptive changes to small intestinal morphology and pepsin activity in weaned piglets.

中文翻译：

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低蛋白日粮对断奶仔猪肠道形态、消化酶活性、血尿素氮、肠道菌群和代谢物的影响

摘要 本研究调查了补充赖氨酸 (Lys)、蛋氨酸 (Met)、苏氨酸 (Thr) 和色氨酸 (Trp) 的低蛋白饮食对小肠形态、酶活性、血尿素氮以及肠道微生物群和代谢物的影响在断奶仔猪中。18 头平均体重 9.57 kg 的断奶猪接受了三种处理中的一种：含有 20% 粗蛋白的正常蛋白质日粮（CP，日粮 [NP]），含有 17% CP (MP) 的适度减少的蛋白质日粮，或低蛋白日粮含 14% CP (LP) 的蛋白质饮食。根据 NRC（2012），所有三种日粮都添加了 Lys、Met、Thr 和 Trp，以满足断奶后仔猪的必需氨基酸需求。在 45 天的研究期后，LP 和 MP 日粮的仔猪表现出萎缩的小肠形态，绒毛高度降低，绒毛高度与隐窝深度的比率降低（p < 0.05）；这两组的胃蛋白酶活性也降低（p < 0.05）。与 NP 组相比，MP 和 LP 组的血浆胆固醇升高和血尿素氮降低（p < 0.05）。总的来说，胃肠激素不受膳食蛋白质水平的影响，除了 MP 和 LP 组中生长抑素水平降低。在任何饮食中，空肠和结肠微生物群在门或属水平上均未受到影响。MP和LP组的结肠氨氮浓度降低。膳食蛋白质水平对短链脂肪酸或生物胺没有影响。我们的数据表明，断奶仔猪日粮蛋白质水平降低 3% (MP) 或 6% (LP) 有可能减少氮排放和消化能力受损。因此，考虑到断奶仔猪小肠形态和胃蛋白酶活性的适应不良变化，日粮蛋白质水平不能降低超过 3%。