Comparing Physiology, Behaviour and Hippocampal Gene Expression in Laying Hens Housing in Differing Experimental Housing Conditions, and that Exhibited Different Housing Preferences
<p>Design of the
housing environment and resources provided may influence the long-term welfare
of commercial laying hens. Accessing nest boxes, perches and foraging materials
appears to be a behavioural priority for hens, but whether the quality of each
alternative is important to their overall experience is unclear. For this
reason, hens were housed in an environment that was designed to be “Preferred”
(P; n = 15) or “Non-Preferred” (NP; n = 15) for 26 weeks. P pens were large and
had deep wood shavings as litter, while NP pens were smaller and had a wire
floor. P pens contained more expansive nest boxes and perches than those in the
NP pens, along with a peat/sand mix dust bath which was absent from the NP
housing. P hens were also given daily positive reinforcers (e.g. food treats),
while NP hens experienced negative reinforcers (e.g. water spray). At the end
of the housing period, a range of physiological and behavioural measures were
taken, and birds were given a series of two-way preference tests between their
experimental housing (either P or NP) and a housing environment intermediate to
both conditions. Tissue was collected from the HF, and the expression of mRNA
transcripts for a range of candidate genes relating to adult hippocampal
neurogenesis (AHN) and glucocorticoid regulation was measured using
quantitative PCR. Preference for the experimental housing relative to the
intermediate conditions was significantly higher for birds housed in P than in
NP conditions. However, no other measure differentiated between hens housed in
the two conditions. A minority of birds from each condition made the unexpected
choice, and serum corticosterone was higher in these individuals than in hens
that made the majority choice. In the caudal HF, expression of doublecortin (<i>DCX</i>) mRNA was also lower in hens that
made the minority choice. The <i>MR</i>/<i>GR</i> mRNA ratio was lower in the rostral
HF of NP housed hens that made the minority choice (in favour of the NP
conditions), which might suggest that this subgroup of birds was the most
stressed. Expression of proliferative marker <i>PCNA</i> was higher in hens that chose the intermediate conditions over
either experimental housing condition. The validity of transcription as a proxy
for AHN in chickens is currently uncertain, and consistency between qPCR assays
was lower when cDNA came from different reverse transcriptions. However, the
existing and novel measures of experience both suggest that variation between
individuals, reflected by their preferences, may exceed differences arising
from an inanimate housing environment designed to be relatively positive or
negative for welfare. </p><p></p><p>Work was approved by the University of Bristol Animal
Welfare and Ethical Review Body and conducted under U.K. Home Office Licences
(PPL: 30/2779 and 30/3392). Animal use and care was in accordance with the
Animals (Scientific Procedures) Act 1986, EU directive 2010/63/EU and the UK
Home Office code of practice for the housing and care of animals bred, supplied
or used for scientific purposes. Collection and post-mortem analysis of tissue
was approved by the Animal Welfare and Ethical Review Body at Newcastle
University (Project ID #549). </p><br><p></p>
