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  • Author: Ø. V. SJAASTAD x
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Premature parturition in sheep following administration of synthetic corticoids is now well documented (Van Rensburg, 1967; Bosc, 1970; Skinner, van Blom, Gouws & Jöchle, 1970; Fylling, 1971). In the cow, both premature parturition (Adams, 1969; Hansen & Christiansen, 1971; Karg, Böhm, Günzler & Müller, 1971; L. E. Edquist, personal communication) and mid-term abortion (L. E. Edquist, personal communication) have been reported following such treatment. Induction of abortion in sheep by synthetic corticoids has not been reported so far. This paper presents a study on the effect of dexamethasone given to ewes during mid-term pregnancy.

Five ewes of the Dala breed, all 80 days pregnant, were included in the investigation. The mean gestational period in this breed is 148 days. The animals received intramuscular injections of 2·5 mg dexamethasone four times

No.5 84 86 88 Days of

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R. Austad, Astrid Lunde and Ø. V. Sjaastad


Plasma oestradiol-17β concentrations in Labradors increased during pro-oestrus to an average maximal concentration of 79·7 ± 10·9 (S.D.) pg/ml, and then fell rapidly. In 6/7 bitches the peak occurred within 1 day of oestrus. No consistent changes in plasma oestradiol levels were observed during pregnancy and at parturition and the values were similar to those in late anoestrus. Plasma progesterone levels did not increase markedly during pro-oestrus. At oestrus, progesterone values rose and maximal concentrations, which varied from about 20 to about 55 ng/ml, were reached within a few days of the oestradiol peak. Plasma progesterone decreased in late pregnancy and in one of the three bitches studied in detail low or undetectable levels were reached 10 days before parturition. In the other two bitches an abrupt decrease in progesterone occurred just before parturition.

Dexamethasone treatment (2 × 5 mg daily for 10 days) from Day 30 of pregnancy resulted in intrauterine death and resorption of the fetuses in the two bitches studied. Treatment from about Day 45 resulted in the birth of dead fetuses at Days 55 and 59 of pregnancy. The changes in plasma oestradiol levels were very small. No changes in plasma progesterone levels were seen when dexamethasone was given in late pregnancy, but an accelerated decline occurred after treatment in mid-pregnancy.