The neuro-endocrine system controls an animal's adaptability to its environments by releasing psychotropic compounds such as catecholamines such as epinephrine (EP), norepinephrine (NE) and dopamine (DA) as well as corticosterone (CORT) and serotonin (5-hydroxytryptamine; 5-HT).

First-named author, F.F. Yan of Purdue University and co-authors there and with USDA-Agricultural Research Service report in their paper in Poultry Science that changes of these neuroendocrine compounds have been used as biomarkers of animals’ stress responses associated with their well-being.

Assuming that pullets, like laying hens, are highly motivated to perch, the group hypothesised that pullets with access to perches will experience less stress than pullets that never have access to perches.

The objective of their study was to examine the effects of perch access and age on physiological measurements of stress in White Leghorn pullets housed in conventional cages.

DAy-old chicks (n=1,064) were randomly assigned to 28 cages. Two parallel metal round perches were installed in each of 14 cages assigned the perch treatment, whereas control cages had no perches. Two birds per cage were bled at four, six and 12 weeks of age. Plasma levels of CORT, DA, EP and NE, blood concentrations of 5-HT and Trp, and heterophil to lymphocyte ratios were measured. Data were analysed using a two-way ANOVA.

Neither the perch treatment nor its interaction with age affected any parameter measured in the study.

The increase in the concentrations of circulating EP, NE, 5-HT (numerical increase at week 4), and Trp in four- and six-week-old pullets compared with 12-week-old pullets is unclear but may have been due to acute handling stress at younger ages.

In contrast, concentrations of DA were lower at four weeks than at six and 12 weeks of age.

Plasma CORT levels and the heterophil to lymphocyte ratio - which are indicators of long-term stress - were unaffected by age (P=0.07 and 0.49, respectively).

These results indicated that age, but not perch access, affects neuroendocrine homeostasis in White Leghorn pullets, Yan and co-authors concluded. Pullets that were never exposed to perches showed no evidence of eliciting a stress response.

Reference

Yan F.F., P.Y. Hester, S.A. Enneking and H.W. Cheng. 2013. Effects of perch access and age on physiological measures of stress in caged White Leghorn pullets. Poult. Sci. 92(11):2853-2859. doi: 10.3382/ps.2013-03271

December 2013