Feather pecking is a typically abnormal behavior that significantly impacts breeding efficiency and animal welfare in the egg production sector. Serotonin (5-HT) is essential for neuronal development and behavioral regulation. This study evaluated the effects of birds’ behavioral development (including feather pecking) and changes in serum hormones in chickens followed in ovo injection of 5-HT. On day 11, incubated eggs were injected with 5-HT at 0 (saline control), 5 ug (low) or 15 ug (high) (n = 166 per treatment). The hatched female chicks were raised under similar conditions up to 20 weeks of age (n = 60 per treatment). Birds’ behaviors were recorded using a digital video recording system. The time to first vocalize and first move, along with the duration of vocalization and escape attempts during the isolation test, during isolation test were analyzed on day 1, and week 4, 8, 12, 16 and 20. Blood samples were collected followed behavioral tests (n = 5/treatment). The expression of 5-HTR1A genes in the hypothalamus was measured by real-time PCR. Compared to controls, 5-HT administrated pullets had greater body weight (P < 0.05) with an improved feed conversion rate (P < 0.05) as well as higher serum concentrations of norepinephrine (NE) regardless of their doses. In addition, serum dopamine (DA) concentrations were lower in both high- and low-dose pullets at 8 and 12 weeks of age (P < 0.05). Also, a decrease in fearfulness response was observed based on the test to vocalize and duration of vocalization (P < 0.05). Further, this exhibited a lesser frequency of total aggressive behavior compared with the chicks in the control group, especially at 8 weeks of age (P < 0.05), where it is associated with elevated serum 5-HT concentration and upregulated hypothalamic expression of 5-HTR1A (P < 0.05). The changes of these hormone concentrations and gene expressions suggested that 5-HT accumulation in early embryonic stages may alter both the adrenergic and serotonergic systems, which could further regulate the isolation behavior and improve birds' growth performance to a certain extent.

啄羽是一种典型的异常行为，会显着影响产蛋部门的育种效率和动物福利。血清素 (5-HT) 对神经元发育和行为调节至关重要。本研究评估了鸟类行为发育（包括啄羽）和蛋鸡血清激素变化的影响注射 5-HT。在第 11 天，为孵化的卵注射 0（盐水对照）、5 ug（低）或 15 ug（高）的 5-HT（每次处理 n = 166）。孵化的雌性小鸡在类似条件下饲养至 20 周龄（每次处理 60 只）。使用数字视频记录系统记录鸟类的行为。在隔离测试的第 1 天和第 4、8、12、16 和 20 周分析隔离测试期间第一次发声和第一次移动的时间，以及在隔离测试期间发声和逃跑尝试的持续时间。收集血液样本，然后进行行为测试（n = 5/治疗）。通过实时PCR测量下丘脑中5-HTR1A基因的表达。与对照组相比，施用 5-HT 的小母鸡体重增加（P  < 0.05），饲料转化率提高（P  < 0.05) 以及更高的去甲肾上腺素 (NE) 血清浓度，无论其剂量如何。此外，在 8 周龄和 12 周龄时，高剂量和低剂量母鸡的血清多巴胺（DA）浓度均较低（P  < 0.05）。此外，根据发声测试和发声持续时间观察到恐惧反应减少（P  <0.05）。此外，与对照组的雏鸡相比，这表现出较低的总攻击行为频率，尤其是在 8 周龄时（P  < 0.05），这与血清 5-HT 浓度升高和下丘脑 5-HT 表达上调有关。 HTR1A ( P < 0.05)。这些激素浓度和基因表达的变化表明，胚胎早期5-HT的积累可能会改变肾上腺素能和5-羟色胺能系统，从而在一定程度上进一步调节隔离行为，改善鸡只的生长性能。