Have you ever heard of the sheep named Dolly? She was the first example of successful cloning of a mammal from an adult cell about 21 years ago. Well, how would you feel if someone started to clone horses? Milanne Rehor hopes technology can resurrect the now extinct Abaco Island horse breed. The death of a horse named Nunki in a Bahamian forest in July 2015, marked the end of the Abaco Island horse. But since technology has advanced quite far, the extinction may be temporary. Milanne Rehor, head of the Wild Horses of Abaco Preservation Society, has received approval from the Bahamian government for an ambitious plan: using Nunki’s DNA and selective breeding to clone the breed back into being.
Nunki died in 2015, but plans are in progress to clone her, in an effort to bring back the Abaco Island Horse. It is still a mystery how horses first came to the Abacos, an archipelago in the Bahamas, but the herd’s roots can be traced to the steeds brought by Spanish explorers to the Americas 500 years ago. Back in the 1960s, the population was around 200 until a child died while trying to ride one of the horses. The locals responded by killing all but three.
When Rehor arrived in 1992 — drawn to the islands by a love for the sea and a fascination with the equines — the population had rebounded to an evolutionarily shaky 30 individuals. Although numbers were up, genetic diversity had plummeted, leaving them vulnerable. Then, in 1999, Hurricane Floyd drove the horses from the pines to a citrus farm, where a pesticide-riddled diet caused toxins to accumulate in their bodies. No Abaco Island horses were born after 1999. When Nunki died, the breed disappeared. She had become ill after antibiotic treatment for a cut.
It is not impossible to clone extinct animals yet it comes with limitations. Reviving entire species such as the woolly mammoth is still a ways off, and the only successfully resurrected animal — a subspecies of ibex — died within minutes. But Rehor and the Abaco Island horse have a shot at changing this. Equine cloning has high-profile precedents, such as replication Gem Twist, a gelding and one of showjumping’s greatest athletes. His clones — Gemini and Murka’s Gem —now pass his champion genetics on to new generations.
Upon Nunki’s death in 2015, Rehor had the vision to have a veterinarian collect tissue and send the sample to a Texas cloning laboratory, ViaGen. Technicians cultured the cells, then stored them cryogenically. Nearly every cell in a living animal contains a complete set of that animal’s chromosomes — all the information needed to re-create the animal in full.
In normal fertilization, the oocyte reduces its own chromosomes by half and the sperm provides the second half. When the sperm delivers its share, it triggers the egg to begin the process of becoming an embryo. In cloning, you start with a mature, healthy egg from a donor mare. But instead of fertilizing that egg, you remove all of its chromosomes and replace them with the nucleus from the cell of the animal to be cloned — in this case, Nunki. Now you have an egg with two sets of chromosomes, just as if it had been fertilized. You tell it it’s been fertilized, and then it develops into an embryo.
The embryo itself is cultured for about seven days until it can be deemed viable, and is then transferred into a recipient mare. On average, only about 10 percent of clone embryos develop normally. For every three that are successfully transferred, two will result in pregnancy and one in a live foal. The procedure is costly, but ViaGen has offered Rehor $US2 million in pro bono work. Cloning is hardly guaranteed, but it is possible.
Cloning however will not save the Abaco Island horse in the long run. It may bring Nunki back, but in order to revive the breed, the cloned mares must reproduce. So that’s the where it gets tricky. If you have to keep breeding back to non-Abaco horses then, in the end, you’d end up with a non-Abaco horse. Even if it is too late to revive a herd of pure Abaco Island horses, there’s still value in preserving Nunki’s genes. Clones keep genes alive, and cloned horses can be introduced to herds to breed naturally, cloning offers an amazing opportunity to enhance the gene pool of gene-limited species. Saving Nunki’s genes could one day add outside genetics to a herd facing a bottleneck.
What do you have to say about this type of cloning? Would you agree to it?