Effects of Concanavalin A, fed as a constituent of Jack bean (Canavalia ensiformis L.) seeds, on the humoral immune response and performance of broiler chickens

An experiment was conducted to investigate the effects of the lectin, Concanavalin A (Con A), contained in raw Jack bean (JB) (Canavalia ensiformis, L.) seeds on the immunological response of broilers. A maize-soybean meal basal diet was prepared to which either 2.5, 5, or 10% of ground raw Jack bean (RJB) seeds was added. The RJB seeds contained 24 g Con A/kg on a dry matter basis, as measured by rocket immunoelectrophoresis. Similar diets were prepared by using the same levels of JB after toasting at 190 C for 16 min. In addition, the basal diet was pair-fed to groups of chicks at the level of feed intake of chicks fed the 10% RJB diet. Each diet was fed to six groups of six chicks for 6 wk. At 5 wk, 15 of chicks from each diet were immunized against Brucella abortus (BA) and the anti-BA antibody titers were determined 1 wk later by ELISA. Antibody production against Con A was also measured by the same method. Binding of Con A to intestinal villi and subsequent endocytosis were confirmed by microscopic examination using a specific peroxidase-antiperoxidase-staining technique. Performance was recorded weekly. Feed intake and weight gain were reduced (P < 0.05) only by the diet containing 10% RJB, indicating that broiler chicks can tolerate daily intakes of 100 mg of Con A over 6 wk without affecting growth. Toasted JB diets supported adequate chick performance. The antibody response to BA did not differ with dietary treatment. Serum from chicks fed raw JB also contained antibodies against Con A. The bursa of Fabricius, thymus, spleen, and pancreas dry weights, as a percentage of dry body weight, were not affected by the experimental diets. The data indicated that Con A binds to the cells of the gastrointestinal tract, passes into the general circulation and, eventually, elicits an immunological response without affecting the production of antibodies to BA.