The unusual case of a goat-sheep hybrid has been reported by veterinarians in Botswana.

The animal, which is now six years old, was born naturally from the mating of a female goat with a male sheep sharing the same kraal.

Although such crossings have been reported elsewhere around the world, notably in Chile, Jamaica and Malta, very few result in live births.

Interestingly in this case, the scientists involved found that the hybrid had 57 chromosomes, a number in between that of sheep and goats.

The ram had 54 and the dam had 60 chromosomes, the large structures in the nuclei of cells that bundle up DNA.

Agricultural shows

The intermediate number proved the animal was a real hybrid and not merely a case of mistaken identity.

"Very little is known about hybrids because of their rarity," said Dr Moetapele Letshwenyo, who has published a paper on the animal in the Veterinary Record.

"But one notes that they are derived from two species of animals which are different. It is easier to get a donkey-horse hybrid (mule) or a donkey-zebra (zonkey) because the species involved are closely related in evolution terms."

The hybrid belongs to one of Dr Letshwenyo's co-workers at Botswana's ministry of agriculture.

"In our tradition, the goat and the sheep stay together," Kedikilwe Kedikilwe told BBC News Online.

"I went home one time and my mother said there was this funny creature in my kraal. Nobody has seen anything like it here. I now take it to agricultural shows around the country and everybody is surprised."

High libido

The animal has halfway features. It is white, with an outer coarse coat and inner woolly coat, and its tail hangs down.

The hybrid grew faster than the kids and lambs born in the same month. It also had a very high libido, mounting both goats and sheep even when they were not in heat. This earned the hybrid the name Bemya, or rapist.

This activity never resulted in any pregnancies suggesting the hybrid was infertile, and the animal had to be castrated because it was becoming a nuisance.

Dr Letshwenyo said: "Individual survival once born is not a problem, but continued existence of the 'species' is problematic because with the odd chromosome number, sperm formation is likely to fail hence the hybrid is likely to be infertile.

"This may explain why just before castration it mated with both goats and ewes but none of them became pregnant."

Internal organs

The two men report in their journal paper that the study of such animals may give some insight into why certain pregnancies fail in livestock. They are also interested in the animal's apparent resilience to disease.

"It hardly gets sick," said Kedikilwe Kedikilwe. "Right now, I have an outbreak of foot rot because of the rains. But we never treated the hybrid for foot rot and it is fine. This is very interesting."

Hybrids also tend to be larger than their parent species and this may have some economic value.

"I hate to think that one day it will die," Dr Letshwenyo said.

"We are interested in recording its lifespan and conducting a post mortem to characterise and compare internal organs to those of sheep, and goats and lastly to preserve some tissues for future use."