Learn about cloned horses

Although still controversial, cloning geldings to make breeding stallions with the same DNA has become big business, says Dr Mac.

Learn about cloned horses
The first cloned horse, the mare Prometea. Note the different white markings; equine clones are only 98% identical. Photo: Dr Mac

The first cloned horse, Prometea, a Hafflinger mare, was born on 28 May, 2003 in Italy. Today there are more than 100 cloned horses, with two to three more being born every year.

According to Horse.com, cloning in the equine world is “the advanced assisted reproduction technique (like embryo transfer) and subsequent production of a foal that has the exact same DNA as the donor horse, be it mare, stallion, or gelding.”

How it works
The egg cell, or oocyte, is usually obtained from a donor mare, and the nucleus, which contains the DNA, is removed in a process called enucleation. Skin cells from the horse to be cloned are used to obtain the DNA that would usually be provided by the sperm. The embryo is incubated for seven days, then implanted into a recipient mare.

The donor mare’s egg cell contains mitochondrial DNA in its cytoplasm. This is not removed when the oocyte is enucleated, and forms about 2% of the DNA of the clone. It is the reason that clones are not 100% identical to their progenitor. For one thing, the white markings on clones are very different from those of the original stallion or gelding that donated the genetic material.

Clones have only one parent, often a gelding. Normal foals have two, so the question breed societies ask is, “Who’s your daddy?”

The Fédération Équestre Internationale (FEI) decided to allow clones to compete in international events in 2010. However, clones are only registered as breeding horses by Studbook Zangersheide and the Anglo European Studbook. The Jockey Club, Arabian and Quarter Horse registries do not recognise them.

Smart Little Lena, a Quarter Horse, produced five clones in 2003, but the resulting court case to get them registered was eventually won by the American Quarter Horse Association (AQHA) in 2015. The reasons for refusing to register cloned Quarter Horses are interesting.

The AQHA registration rules state that the only horses eligible for registration are those that result from the breeding of a mother and father (the joining together of an egg cell and a sperm).

In clones, the father (represented by the sperm cell) is missing. The AQHA website states indignantly: “Cloning doesn’t improve the breed; it just makes Xerox copies of the same horses. With clones we’re not moving forward, we’re staying the same.”

In addition, parentage testing is used to identify Quarter Horses; a clone and its progenitor have the same DNA, making this method of identification impossible.

Furthermore, due the high cost, only elite horses are cloned. If they are used for breeding, this will narrow the gene pool, increasing the risk of genetic diseases.

The reason horse societies register clones is that top- performing horses are often geldings. By the time they are mature enough to win big races, their parents are too old to breed. As a result, cloning geldings to make breeding stallions with the same DNA is big business.

Dr Mac is an academic, a practising equine veterinarian and a stud owner.