Shouting the odds

I watch a popular UK daytime show, and quite often the phrase "shouting the odds" is used. What is the meaning and origin of this?

Mike B
Ontario, Canada

At British horse-racing meetings, all the independent bookmakers stand at their stalls "shouting the odds", i.e. announcing the odds they are willing to offer on the various runners. Each bookie does this at the top of his voice to attract the punters' custom at the expense of all the other bookies, and it all makes for a fair old hullabaloo. (VSD)