An experiment was conducted to test the hypothesis that increased dietary Trp is needed in high-Leu diets for growing pigs to prevent a drop in plasma serotonin and hypothalamic serotonin concentrations and to maintain growth performance of animals. A total of 144 growing pigs (initial weight: 28.2 ± 1.9 kg) were assigned to 9 treatments in a randomized complete block design with 2 blocks, 2 pigs per pen, and 8 replicate pens per treatment. The 9 diets were formulated in a 3 × 3 factorial with 3 levels of dietary Leu (101%, 200%, or 299% standardized ileal digestible [SID] Leu:Lys), and 3 levels of dietary Trp (18%, 23%, or 28% SID Trp:Lys). A basal diet that met requirements for SID Leu and SID Trp was formulated and 8 additional diets were formulated by adding crystalline L-Leu and (or) L-Trp to the basal diet. Individual pig weights were recorded at the beginning of the experiment and at the conclusion of the 21-d experiment. On the last day of the experiment, 1 pig per pen was sacrificed, and blood and hypothalamus samples were collected to measure plasma urea N, plasma serotonin, and hypothalamic serotonin concentrations. Results indicated that increasing dietary Trp increased (P < 0.05) hypothalamic serotonin, whereas increases (P < 0.05) in average daily gain (ADG) and average daily feed intake (ADFI) were observed only in pigs fed diets containing excess Leu. Increasing dietary Leu reduced (P < 0.05) ADG, ADFI, and hypothalamic serotonin. However, the increase in ADG and ADFI caused by dietary Trp was greater if 299% SID Leu:Lys was provided than if 101% SID Leu:Lys was provided (interaction, P < 0.05). Plasma Leu concentration was positively affected by dietary Leu and negatively affected by dietary Trp, but the negative effect of Trp was greater if 299% SID Leu:Lys was provided than if 101% SID Leu:Lys was provided (interaction, P < 0.05). Plasma concentration of Trp was positively affected by increased dietary Trp and increased dietary Leu, but the increase in plasma concentration of Trp was greater if Leu level was at 101% SID Leu:Lys ratio than at 299% SID Leu:Lys ratio (interaction, P < 0.05). In conclusion, increased dietary Leu reduced ADG, ADFI, and hypothalamic serotonin concentration, and influenced metabolism of several indispensable amino acids, but Trp supplementation partly overcame the negative effect of excess Leu. This demonstrates the importance of Trp in regulation of hypothalamic serotonin, and therefore, feed intake of pigs.

中文翻译：

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日粮亮氨酸和色氨酸对生长猪血清素代谢和生长性能的影响

进行了一项实验来检验这样的假设，即在生长猪的高 Leu 日粮中需要增加日粮 Trp，以防止血浆血清素和下丘脑血清素浓度下降并维持动物的生长性能。总共 144 头生长猪（初始体重：28.2 ± 1.9 kg）被分配到 9 个处理中，采用随机完整区组设计，每个区组 2 个区组，每栏 2 头猪，每个处理 8 个重复栏。9 种日粮采用 3 × 3 阶乘配制，具有 3 个水平的饮食 Leu（101%、200% 或 299% 标准化回肠可消化 [SID] Leu:Lys）和 3 个水平的饮食 Trp（18%、23% , 或 28% SID Trp:Lys)。配制了满足 SID Leu 和 SID Trp 要求的基础日粮，并通过在基础日粮中添加结晶 L-Leu 和（或）L-Trp 配制了 8 种额外的日粮。在实验开始和 21 天实验结束时记录个体猪的体重。实验最后一天，每栏处死1头猪，采集血液和下丘脑样本，测定血浆尿素N、血浆5-羟色胺和下丘脑5-羟色胺浓度。结果表明，日粮 Trp 增加会增加 (P < 0.05) 下丘脑血清素，而平均日增重 (ADG) 和平均日采食量 (ADFI) 的增加 (P < 0.05) 仅在饲喂含有过量 Leu 的日粮中观察到。增加膳食 Leu 减少 (P < 0.05) ADG、ADFI 和下丘脑血清素。然而，与提供 101% SID Leu:Lys 相比，如果提供 299% SID Leu:Lys，饮食 Trp 引起的 ADG 和 ADFI 增加更大（相互作用，P < 0.05）。血浆 Leu 浓度受膳食 Leu 的积极影响，受膳食 Trp 的负面影响，但如果提供 299% SID Leu:Lys，Trp 的负面影响大于如果提供 101% SID Leu:Lys（相互作用，P < 0.05 ). Trp 的血浆浓度受到膳食 Trp 增加和膳食 Leu 增加的积极影响，但如果 Leu 水平为 101% SID Leu:Lys 比率，则 Trp 血浆浓度的增加大于 299% SID Leu:Lys 比率（相互作用， P＜0.05)。总之，增加膳食 Leu 可降低 ADG、ADFI 和下丘脑 5-羟色胺浓度，并影响几种必需氨基酸的代谢，但补充 Trp 可部分克服过量 Leu 的负面影响。这证明了 Trp 在调节下丘脑血清素方面的重要性，因此，