RESUMEN
A total of 460 sheep in 3 distinct age/sex groups were examined to determine the occurrence of caseous lymphadenitis in Beni Suef Governorate. The results confirmed that frequency increased with age but also revealed increases in extent of involvement and occurrence of visceral lesion, particularly in association with lesion in the body. An attempt was conducted to evaluate the immunogenic value of toxoid [prepared from C. pseudotuberculosis field isolate] and BCG used in sheep farms. Application of ELISA revealed slight increase in antibody response to toxoid and BCG vaccines prior to challenge, however, at week 7 [1 week post challenge] there was statistical significance elevation of antibody titre in group A vaccinated with toxoid over group B vaccinated with BCG [P < 0.05]. The capacity for induction of memory is a better indicator of vaccine performance and is most effectively assessed by challenge in the natural host. The protection rates post challenge were 71.4%, 42.9% and 14.3% for lambs immunized with toxoid, BCG and non vaccinated group respectively. Generally, the toxoid vaccine [prepared from field isolate] has been shown to confer high but not absolute degree of protection against caseous lymphadenitis and was more efficient than BCG. In sheep, it is likely that a short period of expression is insufficient to induce strong immune response in vivo