Designer life forms are always a tricky process, whether bred in the old-fashioned way like dachshunds or race horses, or done in a lab. The wise breeder/farmer/scientist knows well that a highly specialized form is something that has to be watched and cared for, and that it isn't something that can be left out on its own for long.

Modern agriculture is quite artificial. Many standard crops are hybrids that can't breed true, and must be rebred every season (this is why I spent time in cornfields as a kid picking tassels off the corn). Some of my rosebushes are grafts, and I have to keep trimming suckers off to keep the rose from growing "wild." I didn't know that before one of them did, and I have one healthy, happy rosebush that hasn't busted out with a flower in ten years. You plant a seed from that orange or other fruit you get in the store, and odds are good you aren't going to get the same thing if it grows.

Right now, the common grocery store banana is almost all a single variety--hanging by a thread as a species.

Smart agricultural scientists are working on saving seeds and preserving obscure varieties of plants, knowing quite well that variety will be needed someday. A lot of them are working the banana problem.

As for animals, given time, I have read that all dogs if left in the wild would eventually breed themselves back into a sort of generic Big Yellow Dog.

It's not quite as obvious for horses--the average person who knows little about horses probably couldn't easily tell a Kentucky Derby winner from the herds of wild horses that ran the plains for hundreds of years.

Race horses are not sturdy in some ways, but are cared for at levels far beyond many other animals, and certainly better than the average owned horse.