Effects of dietary egg yolk antibody powder on growth performance, intestinal Escherichia coli colonization, and immunocompetence of challenged broiler chicks.

The present study aimed to investigate the effects of dietary supplementation of different levels of specific IgY (sIgY) and nonspecific IgY (nsIgY) egg yolk antibody powder on growth performance, immune functions, and intestinal morphology of Escherichia coli O78:K80-challenged broiler chicks. Lyophilized antibody isolated by the water-dilution method was obtained from the eggs of laying hens hyperimmunized with E. coli O78:K80. A total of 392 broiler chicks were randomly assigned to 7 dietary treatments with 4 replicates of 14 chicks (7 males and 7 females) each. Before offering the experimental diets, 7-d-old broiler chicks (except the negative control) were challenged orally with 0.5 mL (10(9) cfu/mL) of E. coli O78:K80 suspension. The challenge was continued for an additional 7 d from d 14 to 21 with 1.0 mL of a late log phase culture (10(9) cfu/mL) until the level of E. coli in feces reached 10(5) cfu/g. The 6 challenged groups received a basal diet supplemented with 0 (as positive control), 0.1, 0.2, or 0.4% (wt/wt) sIgY from eggs of immunized hens or levels of 0.2 or 0.4% (wt/wt) nsIgY from eggs laid by the nonimmunized hens. The negative control group was fed with the same unsupplemented diet. Oral infection caused an increase in ileal E. coli enumeration, total blood leukocytes, heterophil:lymphocyte ratio, the concentration of serum and intestinal secretory IgA, and the numbers of jejunal goblet cells and lamina propria lymphatic follicles. After 3 wk of feeding, the levels of 0.2 and 0.4% sIgY and 0.4% nsIgY had the most suppressive effects (P < 0.01) on the ileal E. coli enumeration and secretory IgA concentration. However, serum IgA concentration was slightly decreased only at the presence of 0.4% sIgY and nsIgY. Dietary supplementation with at least 0.2% sIgY decreased (P < 0.05) the circulating heterophil:lymphocyte ratio. Inclusion of both sIgY and nsIgY increased the villus height:crypt depth ratio and decreased the jejunal goblet cells and lamina propria lymphatic follicle numbers, with the most pronounced effects assigned to sIgY-supplemented groups. The best feed conversion ratio was obtained when the dietary inclusion of at least 0.2% sIgY continued for 3 wk. The present results indicate that dietary administration of at least 0.2% sIgY for 3 wk improved the intestinal health indices and immunological responses of broiler chicks orally challenged by E. coli O78:K80.