Abstract
Relationship between immunity and growth rate in chickens is complex and multifaceted. Chicken's immune system plays a crucial role in its overall health, well-being and ability to grow and develop properly. On the other hand, indigenous chickens (ICs) are slow growing but considered to have higher immunocompetence compared to fast-growing commercial broilers. Therefore, this study aimed to evaluate immune responses to sheep red blood cell (SRBC) and phytohaemagglutinin (PHA) in slow-growing chickens, including five different Iranian ecotype ICs and a fast-growing broiler of Ross 308 (R). A total of 600 chicks, 100 from each sex and strain, were raised under identical environmental and management conditions after hatching eggs from five distinct Iranian ICs from West Azerbaijan (W), Khorasan (K), Fars (F), Isfahan (I), Mazandaran (M) and a commercial Ross 308 were collected. To investigate humoral immune responses, two SRBC injections were administered at ages 53 and 60 days, and at 67 days, the haemagglutination method was used to assess immunoglobulin Y (IgY), immunoglobulin M (IgM) and total immunoglobulin (IgT). Additionally, a commercial kit and microplate reader were used to assess the amounts of total protein and albumin/globulin. Cellular immune responses were evaluated by administering a PHA injection. Mainly SRBC responses and plasma protein levels in ICs were higher than R. The PHA responses of R and W were higher than other ICs (p < 0.05). These significant differences may confirm that the immunocompetence of ICs are higher than that in the commercial lines.