Horse of a Different Stripe

By Jamie Murphy

Or, what is that baby zebra doing inside my stall?

In Kentucky, the sight of a horse giving birth is nearly as common as bluegrass. But last week when a 26-year-old mare named Kelly rolled over to foal on the clean straw of her specially lit, rubber-padded stall at a farm outside Louisville, the two attending veterinarians monitored the birth with more than customary anticipation. Reason: the newborn animal that later staggered uncertainly to its feet was a zebra.

The colt is the result of the first successful embryo transfer between two different equine species. A year ago, Veterinarian William R. Foster, who is assistant director of the Louisville Zoo, and Veterinarian Scott D. Bennett of Simpsonville, Ky., synchronized Kelly's reproductive cycle with that of a pregnant Grant's zebra residing at the zoo. Flushing out a ten-day-old embryo from the zebra's uterus with a sterile solution, the two vets implanted it in the womb of the quarter horse. Safely lodged, the embryo gestated for 366 days, slightly longer than the average term for either species.

Foster and Bennett believe that similar feats of embryo transfer will enable the zoo to breed rare equine animals with rapidity. Says Foster: "A zebra's pregnancy normally lasts eleven months. If the embryo is flushed, the female zebra cycles again and can reproduce once more. If we use surrogate recipients, one such zebra can reproduce as many as ten offspring yearly."

Foster deliberately selected an unendangered Grant's zebra (pop. more than 300,000) for his initial experiment. With the newborn's safe arrival last week, however, the scientists will attempt to repeat the experiment with embryos of such rare types of zebras as Grevy's (pop. 15,000), Hartmann's mountain (7,000) and Cape mountain (200).

The cross-species delivery was the third of its kind. Three years ago at New York City's Bronx Zoo, Flossie, a Holstein dairy cow, gave birth to a gaur (rhymes with tower), a rare type of wild ox that inhabits the forests of South Asia. In 1977 two wild Sardinian sheep were born to a domestic sheep at Utah State University.

Embryo transfer among members of the same species is not a zoological novelty. First accomplished in 1890 with rabbits, the technique has since succeeded in hundreds of different mammalian species, including humans.*

In the increasingly competitive U.S. cattle industry, top-pedigreed cows are regularly injected with hormones that cause multiple ovulation. The embryos are then fertilized artificially and relocated in the uterus of a host mother.

Thousands of hybrid calves have been delivered since the process was first used in the early 1970s. Veterinarian Foster hopes that last week's successful birth will presage a more secure future for the world's endangered wildlife. Says he: "This procedure could save whole species from extinction."

--By Jamie Murphy.

Reported by Henry Mayer/Louisville

* The first human to be born as the result of embryo transference was delivered last January to a woman in Los Angeles whose name has been withheld to protect her privacy. The baby boy was reported to be healthy.

With reporting by Henry Mayer