Related to the domestic donkey, the onager is an Asiatic wild ass, which lives in the semi-desert regions of Iran.
The unnamed male was born to first time mum Zarrin on June 10 and keepers say he “is doing very, very well”.
Once common in most of the central and southern plains of Iran, onagers are now found in just two protected areas.
Threatened by illegal poaching, overgrazing and disease passed from domestic livestock, there are believed to be around just 400 left in the wild and very few zoos in the world keep the species.
However, Chester is part of an international conservation scheme and thanks to the success of a breeding programme is helping to ensure these beautiful animals are not lost forever.
Curator of Mammals Tim Rowlands said:
“Our young onager is doing very, very well and Zarrin is proving to be a natural mother.
“The species is critically endangered and so the new foal is a valuable addition to the safety net population found in zoos.
“Sadly, as the rarest species of equid in the world, there is a very real possibility that they could become extinct in the wild and so constant conservation attention is required to secure the future of the species.”