中文摘要：

【目的】研究饲粮中添加色氨酸对仔猪混群后行为、相关激素水平和5-羟色胺受体2A（5-HT2A）基因表达的影响。【方法】将144头体重相近（8.00±0.25）kg的28日龄断奶仔猪随机分为3个处理组,即对照组、处理组Ⅰ和Ⅱ;每组设6个重复,每个重复有8头猪。对照组饲喂色氨酸含量为0.21%的基础饲粮,处理组I和Ⅱ分别在基础饲粮的基础上添加0.1%和0.2%的色氨酸,饲喂28 d后混群,观察猪的争斗行为和日常行为,测定唾液皮质醇浓度、下丘脑5-羟色胺含量和5-HT2A基因表达量。【结果】混群后,与对照组相比,添加色氨酸的处理组仔猪争斗时间和争斗次数显著降低（P〈0.05）,趴卧行为显著提高（P〈0.05）,站立行为显著降低（P〈0.05）,采食、犬坐行为无显著差异（P〉0.05）;随饲粮色氨酸水平的提高,仔猪唾液皮质醇含量显著降低（P〈0.05）,下丘脑中5-羟色胺浓度显著升高（P〈0.05）,下丘脑中5-HT2A mRNA相对表达量依次降低,其中添加0.2%的色氨酸组与对照组相比差异显著（P〈0.05）。【结论】在满足仔猪色氨酸营养需要（0.21%）的基础上,额外添加0.1%和0.2%的色氨酸能提高仔猪下丘脑5-羟色胺的含量,调控5-HT2A基因mRNA的表达水平,降低仔猪混群后唾液皮质醇的含量,进而缓解仔猪混群后的应激行为。

英文摘要：

【Objective】The objectives of this experiment were to evaluate the effects of dietary tryptophan on behavior,concentrations of relative hormones and expression of 5-HT2A mRNA in piglets after mixing.【Method】A total of 144 weaning piglets at 28 d of age with initial average weight at（8.00±0.25） kg were assigned to three groups randomly.Each group included 6 replicates with 15 piglets each.The control group was fed with the basal diet including 0.21% tryptophan,the trentment groups（treatment groupsⅠ and Ⅱ） with basal diets plus 0.1% and 0.2% tryptophan,respectively.Piglets were mixed after diet introduction for 28 d.The aggressive and daily behavior were recorded after mixing and the levels of salivary cortisol,hypothalamic 5-HT and 5-HT2A mRNA were determined.【Result】After mixing,piglets fed with supplemental tryptophan had less time and number of fights and spent more time lying and less time standing（P0.05） than pigs fed with the control diet.There were no significant differences in food gathering and sitting behavior among groups（P0.05）.As the levels of dietary tryptophan increased,the concentrations of salivary cortisol decreased significantly（P0.05）,whereas the concentrations of hypothalamic 5-HT increased significantly（P0.05）.The expression of hypothalamic 5-HT2A in piglets decreased gradually as the levels of dietary tryptophan increased,however,the difference was only significant between the control group and the treatment group Ⅱ（P0.05）.【Conclusion】Surplus 0.1% and 0.2% tryptophan that exceeded the standard requirement for piglets can increase the concentrations of hypothalamic 5-HT concentrations,modify the expression of hypothalamic 5-HT2A mRNA,decrease the concentrations of salivary cortisol,and also alleviatesusceptibility to stress in piglets after mixing.