Abstract
The humoral and cell-mediated immunities to a trivalent killed vaccine, administered subcutaneously to white leghorn-chicken layers at 29 and 31 weeks of age, and containing antigens of infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV), and Newcastle disease virus (NDV), were quantitated in five vaccinated and one unvaccinated-control group. Four out of the five vaccinated groups were immunopotentiated by various combinations of zinc and thymic hormones administered intraperitoneally in a volume of 0.1 ml per bird at an interval of three days for a period of three weeks, starting at 29 weeks of age. At each time interval, each bird of the first group received thymulin (10 ng) and ZnCl2 (1 microM), while each bird of the second group received thymopoietin (25 ng) and ZnCl2 (1 microM); in the third group, each bird received thymulin (10 ng), thymopoietin (25 ng), and ZnCl2 (1 microM), while each bird of the fourth group received only ZnCl2 (1 microM). Birds of the fifth group were only vaccinated and the control birds in the sixth group were left without vaccination or other immunopotentiation. Among all combinations, the thymulin-ZnCl2 resulted in birds with the highest humoral immunopotentiation to IBV, IBDV, and NDV antigens with respective percent increase in the mean titer at 33 weeks of age, compared with initial titer at 29 weeks of age, equivalent to 199%, 671.7%, and 86.4%. The highest cell-mediated delayed hypersensitivity reaction, measured at 48 h following an intradermal administration of the trivalent vaccine in the wattles at 33 weeks of age, was obtained in chickens immunopotentiated by the thymulin-thymopoietin-ZnCl2 combination.