Detta är "The People of Sand and Slag" (2004) av Paolo Bacigalupi. En kort sammanfattning från Wikipedia:
The story follows three genetically modified humans who work as guards for a large mining conglomeration in a far future Montana. It begins with the three of them being called out to track down an intruder on their employer's property. When they finally corner it they realize it is nothing more than a dog. Fascinated by the fact that it could still survive in their day and age they decide to keep it as a pet, and then constantly struggle to keep it fed, clean, healthy and alive.