Relating Adult Hippocampal Neurogenesis to Tonic Immobility and Longitudinal Ranging Behaviour in Commercial Laying Hens
<p>Access to
outdoor areas is provided as a means of enhancing welfare in commercial systems
for laying hens, but proportions of time spent on the range by individual birds
vary substantially. Adult hippocampal neurogenesis in mammals and birds is
upregulated by positive experiences including environmental enrichment and
exercise, while basal levels of proliferation have been associated with
individual differences in reactive versus proactive coping style. We thus
sought to explore whether individual differences in use of outdoor areas and in
tonic immobility (TI) responses (indicative of fearfulness) were associated
with hippocampal cell proliferation and neuronal differentiation. Radio
frequency identification technology was used to track the ranging behaviour of
440 individual focal hens within a commercially relevant system over a 72-day
period, after which tonic immobility durations were measured. Following hippocampal
tissue collection from 58 focal hens, proliferation and neuronal
differentiation were measured through quantitative PCR for proliferating cell
nuclear antigen (<i>PCNA</i>) and
doublecortin (<i>DCX</i>) mRNA respectively.
Variation in ranging was not related to TI responses. Greater time spent in
outdoor areas (the grassy range and stone yard) was associated with higher <i>PCNA</i> expression in the rostral subregion,
while individual differences in TI duration positively correlated with
proliferation over the whole HF. Basal proliferation in the chicken HF may thus
be an indicator of reactivity, while levels in the rostral region may be
stimulated by ranging experience. <i>DCX</i>
expression in the caudal HF negatively co-varied with time on the range, but
was not associated with TI duration. This suggests that ranging outside may also
be associated with stress. Within laying hen flocks, individual differences in
hippocampal plasticity thus relate independently to coping style and use of external
areas.</p><p></p><p>Experimental use of the animals was approved by the Bern Kantonal
Authority (BE-46/16) and the Animal Welfare and Ethical Review Body at
Newcastle University (Project ID #549), and procedures complied with Swiss
regulations regarding their treatment. Standard commercial protocols were
followed, including ad libitum access to food and water. </p><br><p></p>
