Sheep–goat hybrid

A sheep–goat hybrid is a domestic bovid animal created when a sheep and a goat mate. These hybrids are often called "geeps" in popular media, or sometimes "shoats." While sheep and goats look very similar, they belong to different genera within the subfamily Caprinae. Sheep belong to the genus Ovis, while goats belong to the genus Capra. Because these two animals are genetically distinct, their offspring are quite rare. Most sheep–goat pairings result in a stillborn animal. This rarity demonstrates the significant genetic distance between the two species.

The difficulty in creating healthy hybrids stems from differences in their chromosomes. Chromosomes are structures that carry genetic information. Sheep have 54 chromosomes, whereas goats have 60 chromosomes. When a hybrid is formed, it often possesses an intermediate number, such as 57 chromosomes. This mismatch can cause problems during meiosis, which is the process of making reproductive cells. Mismatches during meiosis can lead to eggs with unbalanced genetic complements. This often results in decreased fertility in hybrid females.

Many male hybrids experience a phenomenon known as Haldane's rule. This rule describes how certain hybrid offspring, specifically males, are often sterile. This means they cannot produce their own offspring. Even when parent species have the same number of chromosomes, this phenomenon can occur. In the case of sheep and goats, the differing chromosome numbers contribute to these biological challenges. However, some studies suggest that the specific combination of parent species might influence fertility. For example, a buck–ewe hybrid died in 2018 due to pregnancy-related complications.

History shows that people have observed these animals for centuries. In 1889, Alfred Russel Wallace wrote about the beliefs of shepherds regarding these hybrids. He noted that some believed the offspring could be fertile. Professor Giglioli of Florence provided references to older works on the subject. In 1751, a man named Buffon obtained one hybrid, followed by eight more in 1752. In Chile, these animals are known as "carneros lanudos." In France, they are called "chabin," and in Spanish, they are called "cabruno."

Several confirmed cases of live births have been recorded around the world. In 2000, a male hybrid was born in Botswana. This animal had 57 chromosomes and showed physical traits of both parents. It had a coarse outer coat and a woolly inner coat. It also had long, goat-like legs and a heavy, sheep-like body. In 2014, hybrids were born in both Germany and Ireland. In 2020, a hybrid named Barunka was born in the Czech Republic. She faced health complications and was not easily accepted by sheep or goats.

It is important to distinguish a hybrid from a sheep–goat chimera. A hybrid is the result of mating two parents. A chimera is created artificially by combining two different embryos. Researchers at the Institute of Animal Physiology in Cambridge, England, created the first sheep–goat chimeras in 1984. A chimera is a biological mosaic of cells and tissues. Because it comes from two different embryos, a chimera can have four genetic parents. In contrast, a hybrid only has two.

In a chimera, the individual cells maintain their original species identity. They do not become an intermediate type like a hybrid does. This creates a mosaic effect in the animal's appearance. For example, tufts of goat wool may grow intermingled with ordinary sheep wool. Even if the goat breed used has no wool, the chimera may still grow it. While hybrids face many fertility issues, chimeras are generally assumed to be fertile. Any sperm or egg cell they produce must be either pure sheep or pure goat.