A. Jennifer Morton, Laura AvanzoSo due to ethical issues with testing on macaques, it was acceptable to test on sheep and the studies inadvertently revealed that sheep have a higher brain function than first thought.
Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
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.
Citation: Morton AJ, Avanzo L (2011) Executive Decision-Making in the Domestic Sheep. PLoS One 6(1): e15752. doi:10.1371/journal.pone.0015752
Editor: Georges Chapouthier, Université Pierre et Marie Curie, France
Received: October 13, 2010; Accepted: November 21, 2010; Published: January 31, 2011
Perhaps it would worth undertaking comparative studies with pigs and dogs. Despite claims of pigs being more intelligent than dogs, they are still bred for food. Raising the status of sheep is unlikely to save their chops.
See also New Scientist.