Teddy was never meant to have a name. He was born a number, just one of tens of thousands of dogs—mostly beagles like him, chosen for their trusting, docile nature and compact size—bred in the United States for use in experiments each year. Teddy was meant to live and die in a laboratory, without...

It seemed like a good idea at the time: Buy a house with a two-acre property, let our energetic herding dog have the run of the place and spend blissful summer days digging side by side in the dirt with her. And it was blissful, watching Mattie carve out her napping spots behind the ferns and tall...