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Survival of Multiple Pregnancies Induced in the Ewe Following Treatment with Pituitary Gonadotropins¹

Departments of Genetics and Zoology, University of Wisconsin

Abstract

Follicle-stimulating and luteinizing extracts of sheep pituitary powder have been used to induce superovulation in 25 ewes. Treatment began the twelfth day of the estrous cycle and terminated five days later at the time of natural estrus. All ewes were mated or artificially inseminated.

The viability of the artificially induced multiple pregnancies was checked by observations on different animals at 2 to 5 days, 14 to 27 days, and 30 to 37 days. The numbers of ewes found to be pregnant at the different intervals were 6 of 7, 8 of 10, and 5 of 8, respectively. An average of 9.2 nomral embryos per ewe, representing 70% of the eggs ovulated, was found in the first period, 3.4 in the second period, and 0.8 in the third. Many dead and degenerate embryos were found in the later stages. The corpora lutea numbers of 20.8, 23.2, and 24.6 for the three groups were essentially the same, and it is believed that the initial ovulation and fertilization rates were comparable.

Two possible causes of death are suggested: (1) inadequate uterine environment due either to a direct or an indirect effect of treatment, or (2) abnormalities induced in the ova by the rapid maturation of follicles.

In an attempt to obtain information on the cause of death 26 fertilized ova from treated ewes were transplanted to normal ewes at comparable stages of the estrous cycle. Only three of these survived long enough to interrupt the estrous cycle of the host ewes, but the efficiency of the transplantation technique is unknown, so no conclusion as to their viability is possible.

¹ Paper No. 319 from the Department of Genetics, Wisconsin Agricultural Experiment Station. The work was supported in part by a grant from the Wisconsin Alumni Research Foundation. Further acknowledgment is due to the assistance of personnel provided by the National Youth Administration and the Works Progress Administration.