The barking of the Bay Dogs signals the hunters to release the "catch dogs," that are used to catch and hold. Typical catch dogs include the American Bulldog, American Pit Bull Terrier, Staffordshire Bull Terrier, Boxer and Mastiff crosses. Another name used for a Bay Dog is a "Hog Dogs".

Catch Dogs
Hunting Dogs
Hunting Dogs & their Quarry
Scent Hounds
Sighthounds
Hound Dogs

Bay Dog - Hog Dogs
There are Hog Dog Rodeos which feature Hog-dogs that simulates wild boar hunting with dogs. It requires specially bred  Bay Dog (hog dogs) that are used to bay a hog, wild pig or boar.

Bay Dogs - Curs and Cur Breeds
The word "cur" dates from the Middle English of the 13th century derives from the word "curren", meaning "to growl" - when saying word "Cur" actually sounds like a growl.  Many Curs and Cur Breeds have been given the encompassing title of Bay Dogs. A cur dog is a non specific or a mixture of different breeds of dogs. Bay dogs are popular in America and Australia and the different types were descended from European dogs brought over by immigrants.  These cross breeds of dogs were then mixed with the native dogs with the intention of producing the qualities of hunting dogs and to some extent herding dogs combining features of speed, power, and endurance. Curs often have a wide chest and very little body fat.