|Cheng, Heng Wei|
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2007
Publication Date: 6/16/2008
Citation: Fahey, A.G. and Cheng, H. 2008. Effects of Chronic Intermittent Social Stress on Physical Parameters, Corticosterone Concentrations, and Immune System in two Genetic Lines of White Leghorn Layers. Poultry Science. 87:612-620. Interpretive Summary: Chickens are transported between facilities and mixed with unfamiliar conspecifics at different stages of the life-cycle. This may result in a chronic intermittent social stress (CIS) that could have adverse effects on bird welfare. To examine if bird stress responses are depended on their genetic variations, two genetic lines, DXL (Dekalb XL commercial line) and HGPS (a selected line for High Group Productivity and Survivability) were used in the study. The birds from each line were housed in groups of 8 (542 cm2/bird, experimental birds) and 4 (542 cm2/bird, control birds) between 50 and 58 weeks of age; with 2 birds in the 8-bird cage being moved among the cages within the line on a weekly basis. Body weight, feather score, relative adrenal gland, corticosterone, and T-lymphocytes (cell-mediated immunity) were used as biomarkers to determine the effects of CIS on chickens’ welfare. Results indicate that CIS caused a genetic basis of variations in feather score, adrenal function, and immunity in the birds between HGPS and DXL lines, which was correlated with its line-unique coping ability to social environments and survivability. The finding could be adapted by producers, veterinarians, and other scientists to develop animal well-being standards and guidelines for management practices.
Technical Abstract: Farm management practices such as increasing group size and mixing of unfamiliar chickens may cause chronic intermittent stress (CIS) and impact bird well-being. To examine genetic associated physical and physiological differences in response to CIS, two strains of White Leghorn hens were used in the study, i.e., HGPS (line selected for high group production and survivability), and DXL (Dekalb XL commercial line). Chronic intermittent stress was created when birds were 50 wks of age by increasing group size from 4 birds (control) to 8 birds (experimental) per cage, and providing an unstable social environment by moving 2 birds weekly between cages within the same line (experimental birds only). At 58 wks of age, birds were feather scored. Following euthanization, body weight (BW) and the right adrenal gland weight were collected (n=10 per treatment). Adrenal gland weight was adjusted for BW and adjusted adrenal weight was used for analysis. Plasma corticosterone was quantified using radioimmunoassay. T-lymphocytes (CD4+ and CD8+) were measured using flow cytometry. Results showed that total feather score was worse (higher feather score) for DXL birds than HGPS birds in both the unstressed (P<0.05) and stressed treatment (P<0.01). There was no difference in BW in DXL and HGPS birds between the control and CIS treatments. However, the relative adrenal weight of HGPS birds tended to be lower than control birds following CIS (0.05>P<0.10). Plasma corticosterone was significantly lower in both strains following CIS (P<0.01). T-lymphocyte ratio (CD4+:CD8+) was higher in HGPS birds than DXL birds post CIS (P<0.05). The data indicate that the two strains of birds reacted differently in terms of the adrenal system and immunity in response to CIS. Selection of birds for longevity with kind gentle behaviors and high productivity, such as HGPS birds, provides a useful tool for improving animal well-being.