June, 1955]
B. S. GILL
85
In the experiment on mortality rate among different groups, chicks were given
lethal infection of E. tenella. They suffered the worst type of the disease as revealed
by the high percentage of deaths in them, severest lesions encountered in their
caeca, and marked depression observed in their growth rates. It is here that
differences, if any, in the growth rate of the parasitised chicks affected by the changed
status of their thyroids could be expected to show up. Severe infection markedly
depressed the growth rate of all the three groups. Relative shift in their live weights
before and during the infection, when compared to each other, revealed that the
growth rate of hypothyroid chicks was slightly more depressed than the other two
groups. However, this difference in rate of gain in body weights was not a significant
one.
Body weights taken on the 5th and 8th day of infection revealed a point of
interest. Judging from cessation or depression in growth, the hypothyroid group
was the worst sufferer as it showed a drop of 7.1 per cent in body weight. Then
came, in the order of suffering, infected controls (i.e. with unaltered B. M. R.)
which lost 1.3 per cent body weight during these four days of infection. Hyper-
thyroid chicks, on the other hand, showed a gain of 1.3 per cent in their live weights.
Magnitude of shift in live weights during these four days when worst rigours of the
disease were felt become real when we take into consideration the 17.3 per cent in-
crease in live weights shown by healthy (i.e., uninfected and unmedicated) controls.
The gain of 1.3 per cent in body weight of hyperthyroid chicks, though very slight,
is of considerable significance. It clearly indicates that somehow or other under
the influence of ' protamone ' these birds, though at least five times more densely
parasitised, retained better appetite and digestive efficiency as compared to the
other two lots.
Physiological status of thyroid is known to influence assimilation of carbo-
hydrates and fats [Read, 1950]. Therefore, it may be presumed that hyperthyroi-
dism in the present investigation, perhaps through better maintenance of digestive
efficiency of parasitised chicks, kept their general body vigour relatively at a higher
level which might have been responsible for keeping the mortality rate significantly
lower in them. This investigation has confirmed the findings of Wheeler et al.,
[1948] who observed that birds with depressed and normal metabolic rates suffered
equal loss in body weight due to heavy infection of E. tenella, and birds fed ' prota-
mone ' recorded a comparatively lighter loss in body weight as compared to the
other two groups.
SUMMARY
Effects of induced hypo and hyperthyroidism on parasitism with E. tenella
have been studied experimentally. Presence of several imperfections in similar ex-
periments of Wheeler et al., [1948] and Todd et al., [1949] necessitated the present
investigation as their work had indicated certain important inherent implications
the use of thyroprotein and thiouracil in commercial poultry feeds has got on the
susceptibility of chicks to caecal coccidiosis. Experiments were broad based and
several variables kept constant. Hyperthyroidism stepped up four-fold the rate
of oocyst production as compared to the unmedicated controls ; whereas hypo-
thyroidism slightly lowered the oocyst production. However, this difference was
insignificant. Chicks were given light experimental infection (300 oocysts per