09/02/2026
On July 5, 2024, BLM crews gathering free-roaming horses in central Wyoming brought in one female hinny. By the end of the operation, 2,577 animals had been gathered, and she was the only hinny listed.
A hinny is the less common reverse of a mule. A mule has a donkey father and a horse mother. A hinny has a horse father and a donkey mother. Both usually end up with 63 chromosomes, one fewer than a horse and one more than a donkey, and both are normally sterile.
Not so long ago, we covered mules living among free-roaming horse herds in the American West. Several of you pointed out in the comments that the reverse hybrid should occasionally turn up out there too. At least one has.
The Wyoming hinny was gathered from the North Lander Complex, four BLM Wild Horse Management Areas spread across central Wyoming. The operation ran from July 1 through July 23. On July 5 alone, crews brought in 225 animals. BLM's daily report added a small footnote to the 89 mares counted that day: one was a hinny. Two days later, the agency noted that the animal had been transferred to the Wyoming Brand Inspector.
The record does not explain how she got there. North Lander is managed as a horse complex, not a mixed horse-and-burro population, and BLM does not say whether the hinny was born free, escaped from private ownership, or joined the horses later. That one line in a gather report is almost all we know about her.
In controlled breeding studies, hinnies have proved harder to produce than mules. In a 2023 experiment, researchers inseminated female donkeys with horse semen through 49 reproductive cycles. Only eight pregnancies resulted, a rate of 16.3 percent. In the same experiment, breeding donkey males to horse mares, the cross that produces mules, resulted in pregnancies in six of 14 cycles, or 42.9 percent. Earlier work involving 159 breeding cycles had produced a similarly low 14.5 percent pregnancy rate for hinnies.
Their rarity also makes them surprisingly poorly studied. Mules have actually been put through controlled cognition experiments. In one test, six mules learned a visual discrimination task significantly better than either six ponies or six donkeys. Another experiment found mules completed a barrier-detour task faster than horses or donkeys. Researchers have suggested that some of the physical hybrid vigor associated with mules may extend to cognition.
Ask the same question about hinnies and the science gets thin very quickly. A 2019 review of mule and hinny behavior noted that many of the behavioral comparisons available for mules simply have not been performed on hinnies. Breeders and handlers describe hinnies as sturdy animals with characteristics inherited from both parents, but there is no equivalent body of cognition work showing whether they share the mule's measured advantage.
Hybridization itself does not automatically make an animal smarter. Studies of other hybrids have produced improved cognition, poorer performance and results between those of the two parent species. But researchers studying equid hybrids have specifically raised the possibility that the cognitive advantages measured in mules could extend to hinnies as well. Nobody has yet run the horse-versus-donkey-versus-hinny experiment needed to find out.
There is not even a reliable count of free-ranging hinnies in the American West. BLM's national population tables count federally managed horses and burros separately; hinnies do not have their own population category.
The North Lander female therefore leaves us with a fairly unusual documented case: one hinny living among free-roaming horses in Wyoming, discovered only because thousands of animals were being gathered and counted individually.
Whether she was born out there or simply found her way into the herd remains unknown.
Image is for illustration purposes only
Source: Bureau of Land Management, 2024 North Lander Complex Wild Horse Gather / Anzalone et al., Animals, 2023 / Proops, Burden & Osthaus, Animal Cognition, 2009 / Osthaus et al., Animal Cognition, 2013 / McLean et al., Animals, 2019 / Rice, Frontiers in Ecology and Evolution, 2020.
