Lundgren Kristoffer Anton, Løvlie Hanne
IFM Biology, Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.
Front Physiol. 2023 Sep 12;14:1213986. doi: 10.3389/fphys.2023.1213986. eCollection 2023.
Our production animals typically suffer poor welfare, which can be revealed by measuring the affective state these animals are in. Negative affective state is linked to poorer welfare, and can be measured as fearfulness. While continuing to research how to improve animal welfare, a compliment to reduce negative affective state could therefore be to reduce individuals' fearfulness, similar to how negative affective states are medicated in humans. A proposed mechanism for this is via the monoaminergic systems. This is based on previous studies across species that have linked the serotonergic system and fear-related behaviour. We here aimed to experimentally manipulate the serotonergic system in red junglefowl hens (), the main ancestor of all domesticated chickens. We measured fearfulness as latency remaining immobile in a tonic immobility test, and did so both before and after our experimental manipulation. We set out to experimentally manipulate the serotonergic system via sub-chronic dietary treatment of 5-hydroxytryptophan (the precursor to serotonin). Our dietary manipulation of 5-hydroxytryptophan significantly reduced measured fearfulness in the manipulated hens, while latency in tonic immobility did not significantly change in our unmanipulated, control hens. This finding is promising since it indicates that increased tryptophan levels can be used to reduce fearfulness. Additionally, our result suggests that this can be done non-invasively via food (instead of injections), thus presenting a potentially feasible manipulation also for larger settings. Nevertheless, the serotonergic system is complex and its role in modulating behaviour in the fowl should be explored further to evaluate our findings, and more directly explored also in a production setting.
我们的生产用动物通常福利状况不佳，这可以通过测量这些动物所处的情感状态来揭示。负面情感状态与较差的福利相关联，并且可以作为恐惧程度来衡量。在继续研究如何改善动物福利的同时，一种减少负面情感状态的补充方法因此可能是降低个体的恐惧程度，这类似于人类中对负面情感状态的药物治疗。对此提出的一种机制是通过单胺能系统。这是基于先前跨物种的研究，这些研究将血清素能系统与恐惧相关行为联系起来。我们在此旨在通过实验操纵红原鸡（所有家鸡的主要祖先）的血清素能系统。我们在强直性静止试验中通过测量保持静止的潜伏期来衡量恐惧程度，并在实验操纵前后都进行了测量。我们着手通过对5-羟色氨酸（血清素的前体）进行亚慢性饮食处理来实验性地操纵血清素能系统。我们对5-羟色氨酸的饮食操纵显著降低了被操纵母鸡的测量到的恐惧程度，而在未被操纵的对照母鸡中，强直性静止的潜伏期没有显著变化。这一发现很有前景，因为它表明增加色氨酸水平可用于降低恐惧程度。此外，我们的结果表明这可以通过食物（而非注射）以非侵入性方式完成，从而为更大规模的养殖环境提供了一种潜在可行的操纵方法。然而，血清素能系统很复杂，其在调节家禽行为中的作用应进一步探索以评估我们的发现，并且也应在生产环境中更直接地进行探索。
