Crossbreeding impacts on caecal bacterial count and antibody titres in chickens.

1. A crossbreeding experiment was conducted using 20 sires and 120 dams from each Fayoumi (F) and Rhode Island Red (R) breeds. The F1 chicks of ½F½R and their reciprocal ½R½F crosses were used to estimate direct, maternal and heterotic effects.2. The caecal bacterial counts of Salmonella typhimurium and Enterococcus faecium and the IgA, IgG and IgM antibody titres were determined. Chicks of each genetic group (120 birds) were divided into three groups (40 birds per group) and chicks of the first group were assigned as the control group, while the second group was inoculated with S. typhimurium and E. faecium at 7 and 10 d of age (106 cfu/chick) and the third was inoculated with S. typhimurium at 10 d of age (106 cfu/chick).3. The generalised least square procedure was used to estimate cross-breeding effects. The S. typhimurium counts in the R breed was highly significant, followed by ½F½R cross, ½R½F cross, and F breed. The differences among genetic groups in E. faecium counts and caecal pH was not significant. The estimates of IgA, IgG, and IgM antibody titres were highly significant in the F breed, followed by ½R½F cross, ½F½R cross, and the R breed.4. The estimates of direct additive effects were highly significant F breed for the counts of S. typhimurium and antibody titres of IgA, IgG, and IgM. The maternal effects were highly significant F breed for S. typhimurium, E. faecium count, and antibody titres of IgA, IgG, and IgM. Estimates of direct heterosis were significant for S. typhimurium count and IgA antibody titre but not significant for E. faecium count, caecal pH, and antibody titres of IgG and IgM.5. The results showed that the Fayoumi breed could be used in breeding programmes to improve immunity traits against S. typhimurium in chickens.