Ova Transfer

Always ready to tinker with the basic life processes if they can improve the breed, agricultural geneticists have experimentally transplanted embryos of cows, sheep and mice from high-quality mothers to lower-quality "incubator" females of the same species. Their goal: to allow champion breeders to conceive more offspring in less time, pass on the lengthy trials of pregnancy to their lesser sisters.

Last week, carrying embryo-switching one drastic step farther, three British geneticists reported in Nature that they had successfully transferred female eggs from one species to another.

The three scientists -- R. L. W. Averill, C. E. Adams and L. E. A. Rowson --flushed out newly fertilized ova from the Fallopian tubes of freshly killed pregnant ewes. Then they transplanted the tiny ova to the reproductive tracts of seven female rabbits which had been mated previously with sterilized males to activate their hormone systems. Five days later, the rabbits were killed and the sheep eggs taken out in surgery. The ova had grown as in any pregnancy. Two of the best-developed eggs were replanted in a nonpregnant ewe; 16 days later, the scientists found that the twice-switched eggs had become normal embryos, as healthy as if they had never left their mother's body.

In future experiments, Averill & Co. hope to determine the survival rate of sheep ova in their early development, devise a technique for shipping eggs from the best breeds of sheep in "incubator" rabbits round the world to help sheep growers build new and better flocks.

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