June, 1955]
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of the parasite was higher in chicks with elevated B. M. R. whereas hypothyroidism
had no appreciable effect in this respect. This conclusion is in agreement with and
supports the observation on oocyst production. But oddly enough, birds with
elevated metabolic rate suffered 5.4 and 26.4 per cent lesser mortality than the
birds with normal and depressed B. M. R. respectively. This observation confirms
the findings of Wheeler et al., [1948]. The two observations, i.e. the higher pace of
multiplication of the parasite and lower mortality rate in hyperthyroid hosts are
not easily reconcilable. Though these chicks were actually worst hit by the parasite,
judging from the signs and symptoms, they appeared less affected. They were
more lively and bright. Only on the 5th and 6th day of infection, they were seen
huddled together round the heating arrangement in brooders and showed marked
loss of appetite. Whereas, chicks in the other two lots behaved in this manner
from the late 4th day to the 10th day of infection. Upto the 4th day of infection,
control and hypothyroid birds showed 10 and 27.5 per cent higher rate of gain in
body weights respectively than the hyperthyroid chicks. But between the 5th to
the 8th day (both days inclusive) of infection both the former groups lost consider-
able live-weight. They registered a decrease of 7.1 and 1.3 per cent in body weight
respectively. On the contrary, the hyperthyroid lot actually recorded increase in
body weight during these three days too though the rate of gain in body weight was
impeded. This increase of 1.8 per cent in live weight, though a small one, is of
significance here on comparative basis. These facts tend to show that hyperthyroid
chicks tolerated the infection better than the other two lots. Probably their vitality,
kept up by continued feeding during the infection especially round about the 5th
day-critical stage of the disease, and such other indirect influences tipped the balance
in their favour. Thus it seems that the mortality rate in the parasitised chicks is
not an exact indication of the growth rate of the parasite, but perhaps it points
more truly to the complex phenomenon of the host-parasite relationship.
Thiouracil feeding though resulted in increased fat deposition did not benefit
the birds against Eimeria tenella. Rather, they suffered the highest mortality:
26.4 and 17.5 per cent more than the chicks with elevated and normal metabolic
rates respectively; though it may be recalled that the rate of development of the
parasite in the latter two lots was much higher, and almost the same, respectively
as compared to hypothyroid birds. Further, they gave a more miserable appearance
and showed considerable decrease in their live-weights. Probably their lowered
body vigour was responsible for higher percentage of deaths in them, as hypothyroi-
dism is believed to be associated with a high degree of susceptibility to infections
[Grollman, 1947] and thiouracil is known to produce leucopaenia [Gargill and
Lesses 1945; Warren, 1945]. Whitlock [1945] observed that lambs fed thiouracil
died early of strongylodosis. Todd [1948b] while surveying worm burden of chicks
in Tennessee found that heavy breeds (whose B. M. R. is known to be comparatively
lower, a change artificially induced by thiouracil feeding) harboured greater number
of Heterakis gallinae than the lighter breeds of chicks.
The present investigation which has supported works of Wheeler et al., [1948]
and Todd and his associates [1949] is of interest in commercial poultry farming
where thyroprotein and thiouracil are finding increasing use for conferring one
benefit or the other to chicks. ' Protamone ' feeding has an inherent implication
in that the hyperthyroidism favours a higher rate of oocyst production of
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