Effects of perch access and age on physiological measures of stress in caged White Leghorn pullets
Abstract The neuroendocrine system controls animals’ adaptability to their environments by releasing psychotropic compounds such as catecholamines [epinephrine (EP), norepinephrine (NE), and dopamine (DA)], corticosterone (CORT), and serotonin (5-hydroxytryptamine or 5-HT). 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, we hypothesize that pullets with access to perches will experience less stress than pullets that never have access to perches. The objective of this study was to examine the effects of perch access and age on physiological measurements of stress in White Leghorn pullets housed in conventional cages. Hatchlings (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 were without perches. Two birds per cage were bled at wk 4, 6, and 12 wk 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 analyzed using a 2-way ANOVA. The perch treatment or its interaction with age did not affect any parameter measured in the study. The increase in the concentrations of circulating EP, NE, 5-HT (numerical increase at 4 wk), and Trp in 4- and 6-wk-old pullets compared with 12-wk-old pullets is unclear, but may have been due to acute handling stress at younger ages. In contrast, concentrations of DA were less at 4 wk compared with levels at 6 and 12 wk of age. Plasma CORT levels and the heterophil to lymphocyte ratio, 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. Pullets that were never exposed to perches showed no evidence of eliciting a stress response.