A sheep has a lower level of sentience and it would be more ethical to use a sheep rather than a dog. A dog has a very strong bond with humans and morally, I would feel guilty experimenting on a dog. It all depends on what the objective of the experiment is, if it is something severe or something non-invasive and that can change our perspective depending on the different species' level of tolerance to pain.
I would probably not condone either for animal testing except under the most dire and necessary circumstances. However, if I had to choose under those circumstances I would probably have to say the sheep because a dog seems to have more awareness than a sheep, although I have not known any sheep personally so I could be wrong.
I think that the equality of the model has very little to do with which animal I would condone for animal testing. People are sympathetic to dogs and find them to be more than animals, so I would choose sheep to be the animal that I would run different tests on.
Sheep are better for animal testing because they are already a source of food for humans. It would be more socially acceptable for humans to sacrifice sheep to science than dogs because many people have emotional attachments to their pet dogs, whereas few people have domesticated sheep in their lives.
If both the sheep and the dog are equally good models for animal testing, the sheep should be chosen over the dog. This is because of the fact that dogs have served mankind in more human ways than the sheep. Dogs are more capable of humanity than sheep, and so the sheep should be chosen.
By most measures, dogs are smarter animals than sheep. Sheep should be used for experiments and animal testing rather than dogs for that reason. Plus, humans are used to raising dogs and treating them as house pets, so using them in experiments just seems awkward. Sheep are the best option here.
I think that animal testing is horrible. I would not condone the use of either a sheep or a dog or any other animal they would list. I understand that some animal testing might be beneficial for certain things but there has to be a better way. I do not like animal testing.