In 1981, a Holstein cow - the black-and-white dairy breed that we most often think of when we think of cows - gave birth. There is nothing especially remarkable about that. Lots of Holstein cows give birth to lots of Holstein calves every year. The thing is, this Holstein cow didn't give birth to a Holstein calf. She gave birth to a gaur, an endangered South Asian wild cattle that is also known as the Indian bison. She also didn't deliver her calf on a dairy farm, but instead at the Bronx Zoo. If Flossie (as the mother cow was known) was at all surprised or confused by this outcome, she didn't show it.
After all, she was in decent company.
From the 1980's onward, zoos have been continually experimenting with artificial insemination, embryo transfer, gene banking, and other reproductive technologies. Among the techniques that they sought to perfect were the freezing of sperm, ova, and embryos, as well as the transfer of fertilized embryos into the wombs of other species, which might have been the development that surprised many people the most. Many endangered species breed slowly, having few young at a time which mothers nurture for an extended period of time. With only some many females in a breeding population, that can really slow the growth of the species numbers. The plan was to convert females of other, more common species into carriers of endangered babies... and you don't get that much more common than a dairy cow.
The rule of thumb was that, not surprisingly, these surrogate pregnancies would be most successful if the foster mother and the offspring were of similar, related species. You can't have sheep producing giant panda cubs, obviously. The species which we've had the most success with so far have been ones that have a close analog in either animal agriculture, the pet trade, or animal research. At the Louisville Zoo, for example, a zebra foal was born to a domestic horse. In a more exotic twist, The Baltimore Zoo experimented with raising the embryos of endangered lion-tailed macaques in the uteri of the much more common pig-tailed macaque. Another story involved Dr. Betsy Dresser, formerly of the Cincinnati Zoo, with her baby bongos.
Dr. Dresser was the Director of Research at Cincinnati (currently with the Audubon Center for Research of Endangered Species), a facility which has long been at the forefront of the Frozen Zoo concept. Her goal was transport the embryos of a bongo - an endangered forest antelope from Central Africa - from San Diego back to Cincinnati. But how do you transport temperature-sensitive embryos? Body temperature seemed to be the most efficient, reliably manner. The location on the human body with the most stable temperature is the rectum. Then the mouth. Then the armpit.
She went with the armpit.
When Dr. Dresser stepped off her plane in Cincinnati, five bongo embryos taped in little containers under her arm, she was met with the press. They eagerly photographed her little personal carry-on bag, assuming that was what held the precious endangered embryos. The embryos were later transferred into a female eland, resulting in the birth of a beautiful, healthy baby bongo.
For a brief window of time, artificial reproduction like Flossie the cow's guar calf, or Dr. Dresser's miracle bongo, seemed like it would be the future of zoo reproduction. While such pregnancies and births do still occur, however, they never really became commonplace, largely as a result of funding. There's still so much that is unknown about cryobanking, hormone synching, and, for some endangered species, even the basics of their reproductive biology. For some species, assisted reproduction may be the only hope. For others, it may work best to stay low-tech.
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