The Effects of the Immunogenicity OF Four Isolates of <em>E. Maxima</em> on Performance Indices of Broiler Chickens

Abstract

This study was designed to investigate certain details of immunogenicity, cross immunity and control of four isolates of E. maxima in broiler chickens. The field isolates were obtained from various farms in Georgia and Alabama, United States of America purified through single oocysts isolation. The degree of immunity was measured by the effects of infection on body weight, feed efficiency and pigmentation. Four different isolates of E. maxima (A, B, H, and L) tested were found to be immunogenically identical, but isolate A was more pathogenic. Chickens had substantial immunity 30 days post infection (pi) following five inoculations with E. maxima as measured by lack of oocysts in the feces. Substantial immunity was not achieved in this study until the 30^th day pi. Substantial immunity was not attained until after the fifth inoculation with a dose of 50,000 oocysts of E. maxima by birds that were also allowed access to their infected feces in the litter. At D+5, the non-immunized, non-challenged birds had significantly more (p<0.05) pigment than the non-immunized challenged with isolate A. Birds challenged with isolate A in treatment 4 had significantly poorer feed efficiency (p<0.05) than all the other infected groups. This study indicates that resistance was dependent on the degree of infection and that the exponential increase in the inoculum produced a greater and longer lasting immunity than a single dose of inoculum. The finding in this study is substantiated by the fact that body weight gain, shank pigmentation and feed efficiency of non-immunized, non-challenged controls were no significantly different (p>0.05) from those infected with isolates A, B, or L when challenged, although numerical differences existed.