Comparative Growth and Welfare in Free-Range vs. Conventional Poultry Systems

Thesis Abstract

This study investigates how welfare indicators and growth performance differ between free-range and conventional poultry systems, addressing concerns about animal welfare, productivity, and sustainability in modern poultry production. The problem centers on inconsistent welfare standards and variable growth outcomes across production systems, with limited integrated analyses that jointly assess behavioral, physiological, and performance metrics under real-world management. The aim is to compare growth trajectories, feed efficiency, mortality, health status, and welfare outcomes between system types, and to identify drivers of any observed differences. Specific objectives include (1) evaluating growth rate, final body weight, feed conversion ratio, and mortality across broiler cohorts reared under free-range and conventional housing; (2) assessing welfare via behavioral measures (activity budgets, foraging, fear-inducing tests), physiological stress markers (heterophil-to-lymphocyte ratio, corticosterone levels, inflammatory cytokines), and health indicators (plumage condition, dignity of feather score, incidence of leg disorders); (3) examining environmental and management factors (stocking density, outdoor exposure duration, climate variables, Supplementary vitamin-mineral programs) as moderators of growth and welfare; (4) testing theoretical expectations from the principles of the Welfare Quality® framework and the simultaneous equation framework linking welfare with productivity; and (5) providing evidence-based recommendations for policy and on-farm practices. The study employs a comparative cross-sectional design across two representative commercial farms in temperate regions with similar genetic stock and nutrition programs, incorporating a total of 1,200 broiler chickens per system sampled at days 21, 28, and 42. Data collection integrates quantitative production records, biometric measurements, and welfare assessments, including continuous video-derived activity metrics analyzed via focal sampling and ethogram coding, and physiological assays performed on 10% of the birds per cohort (blood corticosterone by ELISA, H/L ratio by hematology, and inflammatory markers by qPCR). Instrument validity and reliability are established through pilot testing, inter-rater reliability checks for behavioral coding (Cohen’s kappa >0.80), and calibration of laboratory assays with known controls. Data analysis combines descriptive statistics, mixed-effects models to account for repeated measures and farm-level clustering, and multivariate regression to identify predictors of growth and welfare outcomes; ANOVA or ANCOVA will compare group means controlling for covariates such as ambient temperature and stocking density. Structural equation modeling will test hypothesized pathways linking environmental conditions, welfare states, and production performance, while robustness checks include propensity score matching to mitigate confounding. The expected findings anticipate that conventional systems may exhibit higher growth rates and feed conversion efficiency under controlled indoor conditions but poorer welfare indicators due to restricted activity and heightened stress responses, whereas free-range systems may show enhanced behavioral diversity and lower physiological stress indicators but more variable growth performance due to environmental exposure and parasite pressure. The study contributes to knowledge by integrating welfare science with production economics in a field setting, refining methodological frameworks for cross-system comparisons, and providing a validated model that links environmental management, welfare indicators, and performance outcomes in poultry production. The theoretical contribution draws on the Welfare Quality® framework and the animal welfare–productivity interface, with implications for animal welfare policy, certification schemes, and farm management practices. The main conclusion is that welfare-oriented management within free-range systems can be aligned with competitive growth performance through targeted interventions such as controlled outdoor access, environmental enrichment, optimized stocking density, and preventive health programs; recommendations include adopting standardized welfare auditing, implementing climate-adaptive housing, and aligning certification criteria to incentivize practices that simultaneously enhance welfare and productivity. Further research should explore longitudinal designs across diverse climatic zones, genetic lines, and disease challenges to generalize findings and refine intervention strategies.