Possible Clues:

• Once any amount of them, but not so many of them about these days
• They need grooms
• Hoofed mammals (which go with 19 4)
• No longer are, in short, in the pipes for 1 across
• ''If wishes were . . . . . ., beggars would ride''
• Motor's power, informally
• Equine beasts
• They have a sort of hock
• Engine capability, slangily
• Preakness entrants