Go to the dogs
If you speak of 'the dogs' in the UK you be be assumed to be talking about greyhound racing. This has been a popular pastime since the early 20th century. The British Greyhound Racing Board, who use www.thedogs.co.uk as their website address, claim that currently (2008) around 4 million people/year 'go to the dogs'. The expression had long been known with its 'go to rack and ruin' meaning. The addition to the language of the new meaning was referred to explicitly in The Daily Mail, in July 1927:
'Going to the dogs' has... lost... its old suggestion of a descent to dissipation and ruin. Since greyhound racing at the White City... came into existence the expression has suggested a good adventure.
Of course, what originally went to the dogs wasn't a punter wanting a night out but anything decayed and worthless that wasn't fit for humans, particularly food. This usage was well enough established by the late 18th century for it to have become a metaphorical expression; for example, The London Review of Literature, 1775, included a play called Germanicus, A Tragedy:
Sirrah, they are prostitutes, and are civil to delude and destroy you; they are painted Jezabels, and they who hearken to 'em, like Jezebel of old will go to the dogs; if you dare to look at 'em, you will be tainted, and if you speak to 'em you are undone.
That figurative meaning must have been preceded by the literal meaning of giving food that wasn't fit for humans to dogs. In 18th/19th century England, as now, horsemeat wasn't considered suitable for human consumption and it was old and knackered horses that were most likely to be sent 'to the dogs'. This was referred to in The Memoires of the late Thomas Holcroft, 1816:
A rascal, who is a known sharper in these parts, hearing of the aversion I had to cruelty, bought an old, one-eyed horse, that was going to the dogs, for five shillings.
'Go to the dogs' was preceded by the similar phrase 'go to pot', which means much the same thing. It isn't clear if the latter phrase derives from the former or if they were coined independently.