EIMERIA-ACERVULINA - INFLUENCE OF CORTICOSTERONE-INDUCED IMMUNOSUPPRESSION ON OOCYST SHEDDING AND PRODUCTION CHARACTERISTICS IN BROILERS, AND CORRELATION WITH A COMPUTER-SIMULATION MODEL
Eam. Graat et al., EIMERIA-ACERVULINA - INFLUENCE OF CORTICOSTERONE-INDUCED IMMUNOSUPPRESSION ON OOCYST SHEDDING AND PRODUCTION CHARACTERISTICS IN BROILERS, AND CORRELATION WITH A COMPUTER-SIMULATION MODEL, Veterinary parasitology, 70(1-3), 1997, pp. 47-59
An experiment was conducted to investigate the effects of immune respo
nsiveness on excretion of oocysts after E. acervulina infection and su
bsequent effects on production characteristics of broilers (Gallus dom
esticus). These effects were determined in broilers repeatedly infecte
d with 2.85 x 10(3) oocysts of E. acervulina and treated with various
dosages of corticosterone in the diet (0, 10, 20 and 30 p.p.m.). Corti
costerone treatment did not have an effect on the peak oocyst excretio
n, although it was administered from 4 days before initial infection.
The number of oocysts excreted shortly after the peak and the length o
f the excretion period were increased in corticosterone-treated groups
. The absence of a difference in peak oocyst excretion was ascribed to
the existence of a time-lag between first contact with the parasite a
nd rate of development of protective immunity. In a recently developed
computer simulation model this period was assumed to be 5 days. Assum
ing that immunosuppression, through corticosterone, is only effective
when protective immunity is in operation, the results indicate a time-
lag of at least a few days, which supports the inclusion of such a tim
e-lag in the computer simulation model. General immunosuppressive effe
cts of the corticosterone treatment, monitored by antibodies and mitog
en-induced lymphocyte stimulation confirmed that immunosuppression occ
urred shortly after medication started. Infection did not have a signi
ficant influence on production characteristics in animals without diet
ary corticosterone. However. with increasing corticosterone levels the
negative effects of infection on production also increased.