Effect of early testosterone and feather pecking phenotype on brain serotonin - an in vivo microdialysis study in laying hens

Little is known about the neurobiological and maternal factors that increase the vulnerability for compulsive feather pecking (FP) in laying hens. It is proposed that testosterone (T) induced changes in serotonergic (5-HT) neurotransmission increase the risk of developing FP. We investigated the effects of pre-hatch T treatment (in ovo injection of 75ng T on day E0, as a model for increased maternal T, vs. control, i.e. solvent only) on baseline and restraint-stress induced 5-HT release in the amygdala by in vivo microdialysis and high performance liquid chromatography. At the end of the experiment a single subcutaneous fenfluramine injection (0.5 mg/kg) was given to release neuronal serotonin. Subjects were 31 adult White Leghorn laying hens with either an FP and non-pecking phenotype. Effects of pre-hatch T, phenotype, time, and their interactions were analyzed with mixed repeated models. Unexpectedly, restraint did not induce relevant changes of levels of 5-HT and its metabolite 5-HIAA, compared to baseline. Thereafter, restraint was considered baseline. After fenfluramine 5-HT levels strongly increased and 5-HIAA levels decreased. Baseline 5-HT and 5-HIAA levels and fenfluramine-induced 5-HT levels were affected by T x FP interactions. However, when fenfluramine 5-HT release was expressed as percentage of baseline levels, this interaction was not statistically significant. Baseline 5-HIAA levels showed higher levels for FP-T compared to all groups. Baseline and post-fenfluramine 5-HT levels were higher in FP-T than in FP-control hens, with levels of non FP-T and non FP-control hens in between. Thus, feather peckers previously treated with testosterone showed a higher basal 5-HT release and had a larger absolute fenfluramine-induced 5-HT release in the amygdala. This suggests that feather pecking hens may show increased 5-HT neurotransmission if exposed to high testosterone levels in the egg. Further research will focus on the importance of 5-HT in the onset of feather pecking.

Bibliographic Details

Main Authors:	Kops, M., Bolhuis, J.E., Riedstra, B.J., Rodenburg, T.B., Westphal, K.C.G., Korte-Bouws, G.A.H., Olivier, B., Korte, S.M.
Format:	Article in monograph or in proceedings biblioteca
Language:	English
Subjects:	Life Science,
Online Access:	https://research.wur.nl/en/publications/effect-of-early-testosterone-and-feather-pecking-phenotype-on-bra-2
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