Differential responses to heat stress in normal and dwarf chickens: implications for meat quality and immune function

This study investigated the impact of heat stress (HS) on meat quality, antioxidant ability, and immunity in normal and dwarf-size chickens. A total of 144 chickens, with 72 from the normal yellow chicken (NYC) strain and 72 from the dwarf yellow chicken (DYC) strain, were equally divided into groups exposed to heat stress (35±1°C for 8 hours daily) and those kept at 28±1°C as the control group. After seven days of treatment, meat color parameters, including lightness (L*-value), redness (a*-value), and yellowness (b*-value), were assessed. Histopathological examination was conducted on spleen tissues to assess structural changes. Gene expression analysis determined the expression levels of interleukin-4 (IL-4), IL-6, and liver catalase (CAT) related to immune response and antioxidant capacity. HS significantly affected meat color parameters, with an increase in lightness (L*-value) (P<0.01) and a decrease in redness (a*-value) (P<0.01) observed in breast and thigh muscles. Furthermore, HS led to increased drip loss (P<0.05), cooking loss (P<0.05), and shear force (P<0.01) in breast muscles. Histopathological examination of spleen tissues revealed varying degrees of lymphoid depletion, necrosis, fibrosis, and inflammatory cell infiltration in response to HS. Gene expression analysis showed that HS upregulated the expression of interleukin-4 (IL-4) and IL-6 in the spleen of NYC (P<0.05) but not in DYC. Additionally, HS reduced the expression of liver catalase (CAT) in NYC (P<0.05) but had no significant effect on DYC. These findings indicate that HS adversely affects meat quality, immune response, and antioxidant capacity in broilers, with normal-sized chickens being more susceptible to these effects compared to dwarf chickens. The results provide valuable insights into the differential responses of chicken strains to HS and underscore the importance of considering genetic factors in mitigating the negative impacts of heat stress on poultry production.