Although serotonin has been extensively studied in many species, there is a lack of information in ruminants, and no research has been evaluated if its precursor, 5-hydroxytryptophan (5-HTP), administered into the abomasum may be used as a means to manipulate serotonin metabolism. Thus, the objective of this study was to evaluate if intra-abomasal infusion of 5-HTP increases circulating serotonin in the steer. Eight Holstein steers (471 ± 8.9 kg) were used in a replicated 4 × 4 Latin Square design experiment. The treatments were intra-abomasal infusion of 5-HTP at 0.5, 1, 2.5, and 5 mg/kg BW. Blood was collected at 0, 2, 4, 6, 8, and 24 h after infusion. The serum concentration of 5-HTP increased quadratically (P = 0.005) with a peak at 2 h after administration. The 5-HTP administration increased (P < 0.05) serum serotonin in comparison with baseline with no difference (P > 0.05) between the doses of 5-HTP. When 5-HTP was dosed at 2.5 mg/kg BW or higher, intake decreased, and there was an altered manure consistency. The serum 5-hydroxyindole acetic acid concentrations followed the same pattern as 5-HTP. Plasma glucose content was not affected (P > 0.05) by 5-HTP dosing. However, free fatty acids concentration in the plasma was lower (P > 0.05) compared with baseline for the infusion levels of 0.5 and 1 mg/kg BW. Intra-abomasal infusion of 5-HTP efficiently increases serum serotonin cattle.

尽管血清素已在许多物种中得到广泛研究，但在反刍动物中缺乏相关信息，也没有研究评估其前体 5-羟色氨酸 (5-HTP) 注入真胃是否可用作操纵的手段血清素代谢。因此，本研究的目的是评估腹腔内输注 5-HTP 是否会增加公牛中的循环血清素。八头荷斯坦公牛 (471 ± 8.9 kg) 用于重复的 4 × 4 拉丁方设计实验。治疗是腹腔内输注 0.5、1、2.5 和 5 毫克/千克体重的 5-HTP。在输注后 0、2、4、6、8 和 24 小时收集血液。5-HTP 的血清浓度呈二次增加（P = 0.005），在给药后 2 小时达到峰值。5-HTP 给药增加 (P < 0.05) 血清血清素与基线相比，5-HTP 剂量之间没有差异 ( P > 0.05)。当 5-HTP 的剂量为 2.5 mg/kg BW 或更高时，摄入量减少，粪便稠度发生变化。血清 5-羟基吲哚乙酸浓度遵循与 5-HTP 相同的模式。血浆葡萄糖含量不受5-HTP 给药的影响（P > 0.05）。然而，对于 0.5 和 1 mg/kg BW 的输注水平，血浆中的游离脂肪酸浓度与基线相比较低 ( P > 0.05)。腹腔内输注 5-HTP 可有效增加牛血清血清素。