21 There is increasing evidence of a pivotal role of the gut microbiota (GUT-M) in key physiological 22 functions in vertebrates. Many studies discuss functional implications of the GUT-M not only on 23 immunity, growth, metabolism, but also on brain development and behavior. However, while the 24 influence of the microbiota-gut-brain axis (MGBA) on behavior is documented in rodents and 25 humans, data on farm animals are scarce. This review will first report the well-known influence of the 26 MGBA on behavior in rodent and human and then describe its influence on emotion, memory, social 27 and feeding behaviors in farm animals. This corpus of experiments suggests that a better 28 understanding of the effects of the MGBA on behavior could have large implications in various fields 29 of animal production. Specifically, animal welfare and health could be improved by selection, 30 nutrition and management processes that take into account the role of the GUT-M in behavior.

The interaction between the gut microbiota (GM) and the brain has led to the concept of the microbiota-gut-brain axis but data for birds remain scarce. We tested the hypothesis that colonization of germfree chicks from a quail line selected for a high emotional reactivity (E+) with GM from a line with low emotional reactivity (E−) would reduce their emotional behaviour in comparison with germ-free chicks from an E+ line colonized with GM from the same E+ line. The GM composition analysis of both groups revealed a shift in terms of microbial diversity and richness between day 21 and day 35 and the GM of the two groups of quails were closer to each other at day 35 than at day 21 at a phylum level. Quails that received GM from the E− line expressed a lower emotional reactivity than quails colonized by GM from the E+ line in tonic immobility and novel environment tests carried out during the second week of age. This result was reversed in a second tonic immobility test and an open-field run 2 weeks later. These behavioural and GM modifications over time could be the consequence of the resilience of the GM to recover the equilibrium present in the E+ host, which is in part driven by the host genotype. This study shows for the first time that a GM transfer can influence emotional reactivity in Japanese quails, supporting the existence of a microbiota-gut-brain axis in this species of bird.

Background: Recent studies have demonstrated an effect of the gut microbiota on brain development and behavior leading to the concept of the microbiota-gut-brain axis. However, its effect on behavior in birds is unknown. The aim of the present study was to determine the effect of the absence of gut microbiota on emotional reactivity in birds by comparing germ-free (GF) quails to those colonized (COL) with gut microbiota.Material and Methods: From hatching, the quails of both groups GF (n = 36) and COL (n = 36) were reared in sterile isolators. The COL quails were colonized at day 2 by introducing a pool of droppings from conventional adult females into the drinking water and feed. The quails were weighed individually on day 2, 6, and 14. From day 8, emotional reactivity was assessed in each group in the isolators through several behavioral tests.Results: GF quails showed a considerable decrease in emotional reactivity demonstrated by spending less time in tonic immobility during the tonic immobility test (242 s ± 31 vs. 331 s ± 32, p ≤ 0.05), traveling a shorter distance (3,897 cm ± 242 vs. 4,827 cm ± 278, p ≤ 0.05) at a lower velocity (6.55 cm/s ± 0.4 vs. 8.1 cm/s ± 0.5, p ≤ 0.05) during the social separation test and spending more time near an object at the beginning of the novel object test (33.7 s ± 6.4 vs. 18.5 s ± 4.1, p ≤ 0.05). No difference in growth was found between the 2 groups.Conclusion: For the first time, this study demonstrates that the absence of gut microbiota reduces emotional reactivity in Japanese quails in situations of fear and social perturbation without influence on growth.