Acquisition of immunity to Eimeria maxima in newly
hatched chickens given 100 oocysts.
H. D. Chapman, P. L. Matsler, and M.
E. Chapman
Department of Poultry Science,
University of Arkansas, Fayetteville, AR 72701
Corresponding author email address: dchapman@uark.edu
The acquisition
of immunity to E. maxima by chicks infected 18 hr
post-hatch with a single dose of 100 oocysts was investigated.
In the first experiment, birds were moved each day
to clean cages in order to prevent the possibility
of secondary infection resulting from ingestion of
oocysts passed in their feces. Immunity was measured
at 4 wk of age by calculation of oocyst production
following challenge with 500 oocysts or weight gain
following challenge with 100,000 oocysts. Large numbers
of oocysts were produced by infected birds following
challenge although numbers were significantly less
than those from birds that had been reared in the
absence of infection (susceptible controls). The weight
gain of infected birds following challenge was significantly
greater than that of susceptible controls but less
than that of unchallenged controls. Thus only partial
protection had been acquired, whether parasite replication
or bodyweight gain was used to assess the extent of
immunity development. In a second experiment, acquisition
of immunity at 4 wk by chicks infected 18 hr post-hatch
with 100 oocysts of E. maxima and reared in floor-pens
in contact with their droppings was investigated.
Infected birds produced no oocysts following challenge
and weight gains were not significantly different
from the unchallenged controls indicating that full
immunity had developed by 4 wk. It is concluded that
if oocysts of Eimeria species are used to vaccinate
day-old chicks, re-infection by oocysts present in
the litter is necessary for the establishment of protective
immunity.