PhD

A
survey
study
was
conducted
to
assess
the
role
of
hypothyroidism in the etiology of reproductive disorders in goats.
Lowered functional activity of the thyroid was associated with
postpartum anoestrum, repeat breeding and delayed puberty. An
experimental model of controlled hypothyroid state was induced in
goats, using different dose regimes of thiourea with the objective of
studying the sequence of physiopathological changes in hypothyroidism
and its influence on reproduction. Clinically healthy young and adult
cross-bred goats of both sexes were employed for the study. The
animals were divided into control, Treatment I (T1) and Treatment II
(T2) groups. Groups T1 and T2 were administered thiourea orally at
the rate of 50 mg/kg and 100 mg/kg body weight respectively. Clinical
symptoms and growth rate were studied. Protein bound iodine, total
serum protein and serum cholesterol were estimated. Haematological
data were collected and the semen characteristics were evaluated. On
the 90th day of the experiment both control and experimental animals
were sacrificed leaving at least one animal in each group. These
animals were maintained without treatment with thiourea for a further
period of 90 days and sacrificed. Cross lesions and histopathological
changes in tissues were recorded.
Weakness,
lethargy,
depression,
reduced
feed
intake,
subcutaneous oedema of varying degree, loss of libido in males and
anoestrum in females were the important clinical features observed.
There was stunting of growth and apparent reduction in weight of the
animals dosed with thiourea. On discontinuation of treatment with
thiourea all the clinical signs manifested disappeared and the animals
gained weight progressively. There was significantly decrease in the
protein bound iodine, and increase in the total serum protein and
cholesterol level in all the animals dosed with thiourea. The values
reached the normal level on discontinuation of treatment with
thiourea. Microcytic hypochronic anaemia was evident in hypothyroid
goats. There was improvement in haemogram values on withdrawal of
thiourea administration. Reduction in quantity and quality of semen
was observed in hypothyroid goats. The semen appeared normal in
quality and quantity on discontinuation of thiourea administration.
Gelatinisation of subcutaneous fat and hypertrophy and dilation
of the left verntricle were the common findings at autopsy. There was
significant increase in the relative weight of the thyroid, pituitary and
the adrenal gland. Histologically the thyroid glands exhibited varying
degree of hyperplasia and hypertrophy. Predominant histological
changes in the pituitary was hyperplasia and hypertrophy of basophil
cells and degenerative changes in the acidophils. Adrenal gland showed
hypertrophy and depletion of fat in the zona fasciculata. On
discontinuation of treatment with thiourea all the lesions disappeared.
A significant decrease in the relative weight of the testis and
epididymis was observed in all the goats dosed with thiourea.
Histologically the seminiferous tubules were small and lined by single
layer of spermatogonial cells. Some tubules contained degenerated and
desquamated cells without any evidence of sperms. The tubules of the
epididymis were small in size and the lining cells showed deciliation
and desquamation. These degenerative changes were found to be
reversible on discontinuation of treatment with thiourea. The accessory
sexual glands, the seminal vesioles and the prostate weighed less in
hypothyroid goats. Histologically the cells lining the glands were small
inactive,
vaculated
and
hyalinised.
After
discontinuation
of
administration of thiourea the reparative changes were almost normal.
There was significant decrease in the relative weight of the ovary and
uterus in all the animals dosed with thiourea. Histologically ovaries
were found to be inactive and only few scattered immature follicles
were seen. Uterine glands were few and non secretary type. The lining
epithelial cells did not show active mitosis. On discontinuation of
treatment with thiourea the weight of the ovary and uterus increased
and histologically ovaries and uterus were found to be normal. Kids
and
female
goats
were
more
susceptible
to
the
effects
of
hypothyroidism. The significant pathological changes observed in the
reproductive organs have clarified the importance of hypothyroidism
in inducing sub-fertility and infertility in goats. The reversible nature
of the lesion was also proved.