The objective of this study was to evaluate the effect of cottonseed meal (CSM) treated with sodium bentonite (SB) on humoral immune response of laying hens. Nine mash diets in a CRD experiment with a 3 × 3 factorial arrangement with 4 replicates of 8 birds each were fed to 288 Hy-Line W-36 hens from 51 to 63 weeks of age. Nine isocaloric and isonitrogenous diets were comprised 3 levels of SB (0, 1 and 2%) and 3 levels of CSM (0, 10 and 20%). Sheep red blood cells (SRBC) were used as antigen to quantify the antibody response. Two birds per replicate were injected with SRBC (one ml of 3% suspension in phosphate- buffered saline in breast muscle of each hen) at 60 week of age. After 7 and 14 d of SRBC inoculation, blood samples were obtained from the brachial vein of each hen, and total anti-SRBC, IgG and IgM titers were determined. There was not a significant effect of SB, CSM or their interaction on total antibody response against SRBC inoculation, but IgG was significantly increased in birds fed diet contained 20% CSM at 7 d (7.62 vs. 8.45) and 2% SB at 14 d (2.79 vs. 3.66) after injection of SRBC. The interaction effect of SB and CSM on IgG was significantly different among dietary treatments and birds fed diet with 2% SB and 20% CSM had the higher titer as compared with control group (5.0 vs. 2.5) at 14 d after injection of SRBC. Diet containing 2% SB and 20% CSM significantly decreased hen-day egg production (73 vs. 79%) and daily egg mass (47 vs. 52 g) as compared with control group. High stimulation of humoral immunity and reduction of performance in birds fed diet with 20% CSM and 2% SB indicated that there was a negative correlation between performance criteria, especially egg production and immune response.

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