What does he feed them?

From an AP article at Fox Sports:

Mackey… is known for having superb dogs that seemingly can run forever, wagging their tails and barking at the finish line. He’s quick to praise them as the real stars, all capable of leading the pack, the reason for his victories. So what does he feed these running machines with names like Larry, Hobo, Lippy, Handsome, Rev, Foster and Rapper?

“Rocket fuel,” Mackey says with a laugh.

Click on the Fox Sports link above to read the entire article.