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E. S. E. HAFEZ, T. SUGIE and W. L. HUNT

Summary.

17β-Oestradiol was administered intramuscularly to twentyeight heifers either before, simultaneously with or after a subcutaneous injection of 3000 i.u. of pregnant mares' serum (pms). This was followed by an intravenous injection of 2000 i.u. ofhuman chorionic gonadotrophin (hcg). The animals were bred and slaughtered, the reproductive tract flushed and the ova examined microscopically.

Oestrogen treatment tended to reduce the number of developed follicles when applied before pms, but it significantly increased the number when applied after pms. The proportion of follicles which ovulated was not affected by oestrogen. In a group treated with oestrogen after pms, the number of fertilized ova per cow ranged from six to seventeen with an average of 11·3 which was considered an improvement over superovulated cattle not treated with oestrogen. There was no evidence that the rate of tubal transport of ova was altered by the oestrogen therapy applied.

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R. R. MAURER, W. L. HUNT and R. H. FOOTE

Summary.

Repeated superovulation and in-vivo collection of ova were carried out with thirty does divided into three groups of ten does each. One group received fsh—lh, a second group received pmsg—hcg and the controls received only lh. Injections of fsh—lh at three 16-week intervals followed by one 8-week interval resulted in 46·5, 35·4, 25·2 and 18·0 ovulation points/doe. This decrease with time was significant (P<0·05). Corresponding values for the pmsg—hcg group which, however, received fsh—lh for the final superovulation were 13·6, 5·7, 6·2 and 20·3. The lh controls averaged 7·8, 7·0, 5·1 and 5·6 ovulation points. Overall treatment differences were highly significant (P<0·005). From the 1920 ovulation points 1593 ova (83%) were recovered, of which 83·1% were cleaved. Young born from unrecovered ova accounted for 3·1%.

Control kindlings by the same does at regular periods resulted in normal litter size but in fewer does kindling as the experiment progressed. Results of two bio-assays for antihormones suggested that this decrease was due to hormonal refractoriness which was most pronounced in the pmsg—hcg group.

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R. R. MAURER, W. L. HUNT, L. D. Van VLECK and R. H. FOOTE

The ability of transferred ova to develop normally during the pre-natal and early post-natal periods has received only limited attention in the rabbit (Venge, 1950, 1953). This investigation was undertaken: (1) to determine the pre-natal survival of transferred ova obtained from superovulated and normally ovulated does, and (2) to compare early post-natal development of young rabbits resulting from transferred and non-transferred ova.

Superovulated ova obtained from ten does receiving follicle stimulating hormone and luteinizing hormone (fsh—lh treatment) and from ten does receiving pregnant mares serum and human chorionic gonadotrophin (pmsg— hcg treatment) were compared with ova recovered from ten does receiving only lh (Maurer, Hunt & Foote, 1968). Ova were collected in vivo from anaesthetized does 26 to 32 hr after the injection of lh or hcg and transferred to the recipients within 30