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THYROIDAL ACTIVITY AND CÆCAL COCCIDIOSIS
[Vol. XXV, Part II,
Eimeria tenella, which would help in building very high concentrations of infective
oocysts on poultry farm. Chicks from hatcheries and brooders are highly susceptible
to coccidiosis and when put first on such floors may pick up lethal doses of E. tenella
with consequent high mortality and poor performance of survivors. Unless the
farmer recognises this potentially dangerous contamination of floors, he stands to
lose the advantage gained through ' protamone' feeding because of high chick
mortality (due to coccidiosis) in his flocks. Thiouracil feeding not only results in
higher mortality from caecal coccidiosis [present investigation and that of Wheeler
et al., 1948] but also lowers general resistance to infections [Grollman, 1947] parti-
cularly to coryza and Newcastle disease [Shaffner, 1947]. Hence, its use in poultry
feeding schedules warrants and necessitates strict attention to be paid to sanitation
of poultry houses, their floors and runs. Failing this, the advantage gained by its
use on one hand will be lost on the other.
Growth rate of the parasitised chicks
Having investigated effects of thiouracil-induced hypothyroidism and
' protamone' induced hyperthyroidism on the growth of E. tenella, it would be of
interest to compare their effects on the growth rate of the parasitised chicks.
Reduction in B. M. R. accompanying thiouracil feeding, should decrease the
basal energy requirement for maintenance resulting in increased fat deposition
due to the conservation of energy (derived from digested nutrients) left after satisfy-
ing maintenance requirements. Chemical analysis of the entire carcass and com-
parisons between the caloric food intake and caloric value of gains have tended to
bear this out [Andrews and Bohren, 1947]. Thiouracil feeding, in both experiments
(Tables I and II), till the day of infection caused increased gains in weights. Post-
mortem examination of the birds even after they had passed through heavy infection
of E. tenella in two experiments, showed that carcasses of thiouracil-fed lot contained
plenty of deposited fat which was entirely absent in birds of other two lots. This
observation is in accord with that of Andrews and Schnetzler [1946] who also
observed increased fat deposition after thiouracil feeding.
Birds fed with ' protamone ', though were looking more bright and active,
made comparatively poor weight gains. This too was expected in the light of the
fact that the metabolic rate was artificially accelerated, with the result that much
of the energy derived from ingested feed was utilised for supporting the increased
B. M. R. Consequently, little could be left and utilised for increasing the live-
weight.
In the experiment on oocyst production, birds were lightly infected (250 oocysts
of E. tenella each, a dose far below the lethal level). They did not evince any
appreciable effect of infection on their health as the disease produced was a very
mild one. This fact explains that observations on weight gains in this experiment
(Table I) did not record any marked difference in growth rates of various groups of
chicks before and during infection except that the rate of growth of hypothyroid
chicks was proportionately lower for the 10-day-infection period than for
the pre-infection days as compared to the other two lots. But this difference was
not significant. Similarly, Todd et al., [1949] also failed to note any significant
difference in weight gains by lightly infected chicks (50 days old) with normal and
elevated metabolic rates.