A population segregating for the naked neck (Na) gene was used to evaluate its effect on fast growing broilers at heat stress. An experimental stock comparable to those of modern broilers was established by backcrossing to colour synthetic male and female lines. Matings between heterozygous (Na/na) males and females produced normally feathered (na/na), heterozygous (Na/na) and homozygous (Na/Na) chicks for the present study. Day old to seven week old coloured broilers of three genotypes viz. normally feathered (na/na), heterozygous naked neck (Na/na) and homozygous naked neck (Na/Na) were compared for heat dissipation, growth performance, body conformation traits, blood biochemical parameters and carcass traits in tropical climate. In hot climate, naked neck broilers had significantly less body temperature and better heat dissipation capabilities as compared to normal broilers. The naked neck broilers had significantly higher body weight and better feed conversion ratio than na/na broilers. The Na/Na or Na/na broilers exhibited higher giblet yield, blood loss and lower feather mass compared to na/na broilers. The results indicated that the reduction in feather coverage in Na/Na and Na/na broilers facilitates better heat dissipation with lower body temperature, more body weight gain, better FCR and carcass traits compared to normal broilers.

The study was undertaken to evaluate the effect of naked neck gene on mortality, cell mediated and humoral immune response in white plumage broiler population. The mortality of homozygous naked neck (Na/Na) broilers (11.71%) was comparatively lower than that of heterozygous naked neck (Na/na) (12.28%) and normally feathered (na/na) (13.59%) broilers. The humoral immune response was measured against (1% v/v) sheep red blood cells (SRBC) for total haemagglutinin (HA) antibody, 2-mercaptoethanol resistance (MER) or (IgG) antibody and 2-mercaptoethanol sensitive (MES) or (IgM) antibody titre on 7 days post-immunization. The titre was expressed as log2 of the highest dilution which shows complete haemagglutination. Total HA titers of Na/Na and Na/na (11.05±0.53 and 11.09±0.38) were comparatively higher than that of na/na (10.26±0.42). The MES antibody titre of Na/Na (8.50±0.53) and Na/na (7.63±0.45) broilers were significantly higher as compared to na/na (6.11±0.32) broilers. The MER titre of na/na genetic group (4.15±0.42) was significantly higher than Na/Na (2.55±0.37) and comparatively higher than Na/na (3.45±0.38) broilers. In vivo cell response to phytohaemagglutinin-P (PHA-P), measured as Foot Index (FI) in mm expressed significantly higher response in Na/na (0.473±0.05) and Na/Na (0.413±0.04) broilers as compared to na/na (0.304±0.03) broilers. The result of present study suggested that white plumage naked neck broilers had better immune response as compared to normally feathered broilers.