82
THYROIDAL ACTIVITY AND CAECAL COCCIDIOSIS
[Vol. XXV, Part II,
oocyst production for this group. This encouraged growth of the parasite might
either have been due to the direct stimulating effect of the elevated B. M. R. of the
host upon various endogenous stages or that the higher B. M. R. acted as a ' stress
factor ' upon the host by depleting the latter of its essential vitality-keeping factors
like vitamins [Ershoff, 1948]. Consequently, the host tissue offered little or com-
paratively less resistance to the development of the parasite so that the parasite
developed unhindered in thus devitalised tissue, or a possible protective factor,
hitherto unknown, like a ' mucus anthelmintic' factor [Frick and Ackert, 1948]
which ordinarily might be protecting the caecal mucosa against Eimeria tenella
has been adversely affected. Another instance of hyperthyroidism favouring the
parasite is available in the work of Larsh [1947]. While studying the effect of
induced hypo- and hyperthyroidism in young and older mice upon their natural
resistance towards the percentage development of eggs of Hymenolepis nana var.
fraterna into cysticercoids recovered 92 hours post-infection, he found that hyper-
thyrosis favoured heavier parasitisation by cysticercoids indicating lowered resistance
of the host. Thiouracil treatment of mice did not change their resistance towards
Hymenolepis. But the study of Leach and Spence [1951] on Notoedres scabie of
rats that hyperthyrosis raised their resistance to the development of severe lesions,
whereas hypothyrosis had the opposite effect and favoured the mites, is in sharp
contrast to the above noted two observations.
Hypothyroid chicks produced almost the same number of oocysts as did the
controls. It would mean that either the lowered B. M. R. had no direct appreciable
effect upon the parasite, or it did not affect any change in the resistance of the
caecal tissue so that the growth rate of the parasite was proceeding at the same
pace in both the hypothyroid and unmedicated chicks.
Todd [1948a] found that hypo- and hyperthyroidism did not materially change
the resistance of chicks to A scaridia galli and Heterakis gallinae, but the two worm
attained significantly greater lengths in mildly hyper- and hypothyroid birds, respec-
tively. This differential response of the parasite to the changes in B. M. E. of the
host was not understood.
Mortality rate and severity of caecal lesions
Birds kept on thiouracil diet were very dull, registered more loss of appetite
and presented more miserable appearance as compared to the ' protamone '-fed
group. Chicks in the latter lot were definitely more bright and vigorous. Birds in
the ' protamone' group showed marked loss of appetite on the 5th and to some
extent on the 6th day of infection only. On these days, they huddled together
under heating arrangement as done by the birds belonging to the other two groups
from the late 4th day of infection till the 10th day when all the survivors were
sacrificed to note the severity of caecal lesions. Clinically, the control birds were
somewhat less affected than the hypothyroid birds.
Data on the severity of lesions suffered show that the lot with elevated B. M. R.
was definitely worse affected than the other two groups. The latter, as compared
with each other, appeared equally affected. Differences in the lesions caused
indicate the rate at which schizogony has been going on, i e. the rate of develop-
ment of the parasite. Therefore, it can be logically concluded that the growth rate