Abstract

This study investigated the combined effects of stocking density, heat stress, and vitamin supplementation on humoral immune responses and lymphoid organ development in broiler chickens. A total of 720 unsexed Cobb broiler chicks (7 days old) were randomly allocated to 18 experimental groups across three thermal environments: thermoneutral conditions, sudden chronic heat stress (CHS), and gradual CHS exposure. Birds were housed at three stocking densities: recommended (10 birds/m²), medium (14 birds/m²), and high (18 birds/m²), with or without ascorbic acid and vitamin E+Se supplementation. Humoral immune responses against Newcastle Disease Virus (NDV) and Infectious Bursal Disease Virus (IBDV) were evaluated using hemagglutination inhibition and ELISA tests, respectively, at 14, 21, 28, 35, and 42 days of age. Lymphoid organ indices were measured at 42 days. Results showed that heat stress protocols and stocking densities had minimal significant effects on antibody titers against both NDV and IBDV vaccines across most sampling periods. However, gradual CHS exposure at 42 days showed some variation in NDV antibody responses, with the highest stocking density group (G3) showing numerically higher titers (4.33±0.33) compared to supplemented groups. Lymphoid organ development remained largely unaffected by experimental treatments under thermoneutral conditions. The study suggests that broiler chickens demonstrate remarkable resilience in maintaining immune responses despite environmental and housing stressors, though subtle differences may emerge under prolonged stress conditions.

Key words: broiler chickens, stocking density, vitamin supplement, heat stress, immune response