STEROID HORMONE REQUIREMENTS FOR THE MAINTENANCE OF EARLY PREGNANCY IN SHEEP: A STUDY USING OVARIECTOMIZED ADRENALECTOMIZED EWES

in Reproduction

Embryonic development will proceed normally in ewes ovariectomized 4 days after ovulation if the animals are treated daily with progesterone (Bindon, 1971). Oestrogens are required for implantation to proceed in rats and mice (Nalbandov, 1971) but this requirement has not been established for sheep. While oestrogens of ovarian origin have been excluded as being necessary for the establishment of ovine pregnancy, it is possible that oestrogen production by the adrenals could supply any requirements at this time (McLaren, 1973).

Adrenalectomized ewes can be mated and become pregnant (Harrison, Heap & Paterson, 1972) provided they are supplied with glucocorticoids and mineralocorticoids. Tilton, Hoffmann, Light & Buchanan (1971) report that adrenalectomy did not not reduce mating activity, fertilization rate or conception rate.

Reliable estimates of oestrogen production by the adrenal have been difficult to achieve because of the very low secretion rates. Baird (1968) found approximately 1 ng oestrone in each of

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