Influence of early or late start of first feeding on growth and immune phenotype of broilers.

1. The changes in body weight (BW) gain, immune phenotype and viability of commercial broilers, either given feed and water immediately after hatch or food-deprived for 24 or 48 h, were analysed in order to study the effect of early or late start of first feeding. 2. Chickens fed immediately had a 6.1% higher BW at slaughter age than those food-deprived for 48 h, while those chickens food-deprived for 24 h only had a 1.4% higher weight than those deprived for 48 h. 3. Those fed immediately and those food-deprived for 24 h did not differ significantly in BW. 4. Humoral immune status was measured as specific IgG antibody production and concentration of IgM and IgG in serum. Cellular immunological variables were the proportion of circulating leukocyte subpopulations and the relative expression of leukocyte surface markers, including the relative expression of Major Histocompatibility Complex (MHC) antigens. 5. Differences were found between the three feeding treatments in the relative expression of MHC class II molecules, the relative expression of BU-1 molecules, and the ratio of CD4:CD8 single positive cells. 6. For the MHC class II molecules, a lower expression was found on the surface of mainly B-cells in chickens fed immediately compared with the two other feeding regimes. 7. These results suggest that food deprivation for 48 h may be unfavourable to the growth, viability, and the immune performance of broilers, whereas deprivation for 24 h appears to be acceptable for growth and normal immunological performance.