Great Eggs-pectations: Understanding Markers of Stress and Welfare in Pullets Using Feeder Space and Stocking Density Stressors
Creators: name: Abraham, Meagan E
Publisher: name: Purdue University Graduate School
Year: 2022
Subjects: Animal management
Animal welfare
Animal growth and development
Veterinary immunology

description: Little is known about pullet stress and welfare and even less is known about pullets in cage-free housing. The studies included in this dissertation evaluated bird responses to stocking density, feeder space, and ACTH stressors in pullets. The project and procedures were reviewed and approved by the Purdue University Animal Care and Use Committee (Protocol#:2001002002 and # 1908001938). Two studies of external stressors and one study of an internal stressor were applied to Lohmann LB-Lite (Brown) and Lohmann LSL-Lite (White) pullets. For both studies of an external stressor, bird-based welfare parameters included evaluation of bird appearance through feather coverage, foot condition, and keel condition; blood parameters, i.e., cholesterol, corticosterone, cortisol, NDV/IBV IgG/IgY titer, and differential WBC (%) and heterophil to lymphocyte ratio; measurements of the spleen, bursa, thymus, and liver; and production values measured through body weight, body weight uniformity, shank length, feed consumption, and feed conversion ratio (FCR). Birds were followed from 2-16 weeks of age (WOA) for the external stressors and were housed on the floor. The first external stressor was applied through a 2 x 2 factorial randomized complete block design (RCBD) using Brown and White strains and two stocking densities- high (HSD) and low (LSD). Stocking densities were adjusted over time, with the ending density of 670 cm2/bird for HSD and 1352 cm2/bird for LSD at 16 WOA. Density alone affected relative bursal weight (%), with LSD generating heavier bursas. LSD also generated lower, better FCR for both white and brown strains though this difference was not statistically significant. Within a density, opposing strain effects were seen for body weight uniformity and feather coverage. White was improved at HSD while Brown was improved for LSD. The second external stressor study was a 2 x 2 x 3 factorial RCBD with Brown and White, 2 feeder space allocations (3.5 or 7 cm/bird), and 3 stocking densities. The ending stocking densities were 154.45, 518.76, and 1,247.38 cm2 for the high (HSD), medium (MSD), and low (LSD) stocking density treatments, respectively, at 16 WOA. In this study, less space per bird was associated with poorer feather condition but improved FCR. Reduced feeder space was associated with elevated or worse FCR. In a study of internal stressors, ten each of Lohmann LSL-Lite hens received either a saline-mannitol or synthetic human ACTH injection at 6, 17, and 26 weeks of age. Blood was collected prior to injection and 1- and 2-hours post-injection. H:L ratio, WBC differential counts, corticosterone, and cortisol were measured in blood. Albumen samples were collected to measure corticosterone and cortisol at 26 WOA only but were unaffected by treatment. Serum corticosterone and H:L ratio were also unaffected by treatment. Serum cortisol was increased 1 hour after ACTH injection at 17 and 26 WOA and percent heterophils and lymphocytes were affected by ACTH at 26 WOA indicating potential utility as a measure of stress for adult birds only. The results of these studies show that pullets are resilient and resistant to several stressors. Both acute and chronic as well as internal and external stressors were tested in these studies with limited effects on the birds’ physiology, immunity, condition, or production. Feather coverage and bursal size were improved at lower stocking densities and FCR was improved at greater feeder space but the implications of these differences are unclear. Further research is needed to identify why there are reduced stress responses in pullets; it is possible that domestication or preserved evolutionary pathways explain some of the differences between pullet and adult stress responses. And while the majority of parameters were unaffected by the stressors used, the results of this study presented baseline values for Lohmann LB-Lite and Lohmann LSL-Lite pullets that will help guide future research. Additionally, the results of these studies left perhaps more questions than answers but illustrate perfectly that more research will be critical to an understanding of pullet stress and welfare.