To go to the dogs

to get worse or become ruined

since our favourite restaurant got a new chef the food has gone from excellent to poor; it’s gone to the dogs.

More than one possible source of the idiom exists. One is that as far back as the 1500s, bad or stale food that was not thought to be suitable for human consumption was thrown to the dogs. The expression caught on and expanded to include any person or thing that came to a bad end, was ruined, or looked terrible.