Early life microbiota transplantation affects behaviour and peripheral serotonin in feather pecking selection lines

Early life environmental factors have a profound impact on an animal’s behavioural andphysiological development. In animal husbandry, early life factors that interfere with thebehavioural and physiological development could lead to the development of damagingbehaviours. The gut microbiota could be such a factor as it influences behaviour, such as stressand anxiety, and physiology, such as the serotonergic system. Stress sensitivity, fearfulness andserotonergic system functioning are related to feather pecking (FP), a damaging behaviourin chickens which involves pecking and pulling out feathers of conspecifics. Furthermore,high (HFP) and low FP (LFP) lines differ in gut microbiota composition. Yet, it is unknownwhether gut microbiota affects FP or behavioural and physiological characteristics related toFP. Therefore, HFP and LFP chicks orally received 100μL of a control, HFP or LFP microbiotatreatment within 6 hrs post hatch and daily until 2 weeks of age (n=96 per group) using apipette. FP behaviour was observed via direct observations at pen-level between 0-5, 9-10 and14-15 weeks of age. Birds were further tested in a novel object test at 3 days and 5 weeks of age,a novel environment test at 1 week of age, an open field test at 13 weeks of age and a manualrestraint test at 15 weeks of age after which whole blood was collected for serotonin analysis. Weanalysed treatment effects within lines using mixed models with treatment, batch, sex, observerand test time as fixed factors and pen within treatment as random factor or Kruskal-Wallistests. Early life microbiota transplantation influenced behavioural responses and peripheralserotonin, but did not affect FP. HFP receiving HFP microbiota tended to approach a novelobject sooner and more birds tended to approach than HFP receiving LFP microbiota at3 days of age (P<0.1). HFP receiving HFP microbiota tended to vocalise sooner comparedto HFP receiving control (P<0.1) in a novel environment. LFP receiving LFP microbiotastepped and vocalised sooner compared to LFP receiving control (P<0.05) in an open field.Similarly, LFP receiving LFP microbiota tended to vocalise sooner during manual restraintthan LFP receiving control or HFP microbiota (P<0.1). LFP receiving HFP microbiota tendedto have lower serotonin levels compared to LFP receiving control (P<0.1). Thus, early lifemicrobiota transplantation had short-term effects (during treatment) in HFP birds and longtermeffects (after treatment) in LFP birds. Previously, HFP birds had more active responsesand lower serotonin levels compared to LFP birds. Thus, in this study HFP birds seemed toadopt behavioural characteristics of donor birds, while LFP birds seemed to adopt physiologicalcharacteristics (i.e. serotonin level) of donor birds. Interestingly, homologous microbiotatransplantation resulted in more active responses, suggesting reduced fearfulness.