Abstract: To investigate the effect of yogurt with different storage times on the immunity of immunized initiatively mice by New Castle Disease(NDV). 36 male mice were divided into four groups. Control group(CON), Experiment group 1(E1), Experiment group 2(E2) and Experiment group 3(E3) had been fed yogurt respectively without storage, or after stored 3d, 6d and 9d(after the date yogurt was out of factory) of storage times with the general diet. Every mice was fed yogurt 1ml/d successively for 7d(the Lactic Acid Bacteria were counted before fed to mice). On the eighth day, all the mice were injected subcutaneously Newcastle Disease Virus 0.2 ml per mouse. Then they were continue to be fed yogurt successively for 10d. On the 18th day, all the mice were killed for the determination of the influence of yogurt with different storage time on the secretion of sIgA in intestinal, the hemagglutination inhibition (HI) titer, the level of IL-2 in serum, and the level of Tumor Necrosis Factor(TNF) in spleen. The number of LAB in yogurt with 3d of storage increased by 656.26%(p<0.01) than that without storage, while those with 6d and 9 d storage decreased 40.15%(p<0.05) and 65.46%(p<0.01) respectively. The level of sIgA in intestinal, the hemagglutination inhibition (HI) titer of NDV and the Tumor Necrosis Factor(TNF-α) in spleen of the mice in the group fed yogurt with 3d storage time increased by 8.04%,10.35% and 9.70% respectively than control group fed yogurt without storage time. The level of IL-2 in serum increased by 23.11%(p<0.05).All the index of immunity in the group fed yogurt with 6 and 9 storage times were lower than control, and the latter were lowesy. The correlation analysis showed that there was significant correlation between IL-2 and the number of Lactic Acid Bacteria(LAB)in yogurt. This study showed that the storage of yogurt had affected the number of the viable lactic acid bacteria in yogurt, and then indirectly affected the immunostimulatory effect of yogurt on the body immunized initially. Yogurt within 3d storage time showed good immunostimulatory effecet, so the 3d storage time was the best.

Key words: yogurt, lactic acid bacteria(LAB), storage, immunity