Further to the above post, the answer lies not in the fact that the 'goods' in question are livestock- the answer lies in the contract. It wouldn't matter if the sale was a dog, a sheep or a cup, the same provisions apply (assuming that the person isn't paying HP or receiving a service.)
There is no legal provision stating that the purchaser has a right of refund where the goods are OK- that is, fit for their purpose, as described etc etc. This surprises some people, but it's done as a matter of commercial certainty- if a company could have someone bringing back the goods for a refund, profits could be harmed, and a company could find themselves in a real mess if they've used the money received elsewhere. The courts rely on the principle 'let the buyer beware'. Thus, presuming the dog is the correct breed, no refund is mandatory.