In studying a defective gene known to cause Huntington’s disease, researchers found that sheep are able to pass a number of tests that are typically given to humans with Huntington’s disease. Cognitive testing found that sheep have the ability to distinguish between different pairs of colors or object shapes. Moreover, they demonstrate they ability to recognize each others’ faces, remember significant others for at least two years, and discriminate between breeds of sheep. There is also evidence that sheep can correctly categorize plants in groups of families, navigate their way through a maze, and develop more complex social interactions. Males appear to form long-term bonds with other males and support these partners in fights.

Article Abstract:

“Two new large animal models of Huntington’s disease (HD) have been developed recently, an old world monkey (macaque) and a sheep. Macaques, with their large brains and complex repertoire of behaviors are the ‘gold-standard’ laboratory animals for testing cognitive function, but there are many practical and ethical issues that must be resolved before HD macaques can be used for pre-clinical research. By contrast, despite their comparable brain size, sheep do not enjoy a reputation for intelligence, and are not used for pre-clinical cognitive testing. Given that cognitive decline is a major therapeutic target in HD, the feasibility of testing cognitive function in sheep must be explored if they are to be considered seriously as models of HD. Here we tested the ability of sheep to perform tests of executive function (discrimination learning, reversal learning and attentional set-shifting).”

“Significantly, we found that not only could sheep perform discrimination learning and reversals, but they could also perform the intradimensional (ID) and extradimensional (ED) set-shifting tasks that are sensitive tests of cognitive dysfunction in humans. Their performance on the ID/ED shifts mirrored that seen in humans and macaques, with significantly more errors to reach criterion in the ED than the ID shift. Thus, sheep can perform ‘executive’ cognitive tasks that are an important part of the primate behavioral repertoire, but which have never been shown previously to exist in any other large animal. Sheep have great potential, not only for use as a large animal model of HD, but also for studying cognitive function and the evolution of complex behaviours in normal animals.”