What do the Houyhnhnms do that Gulliver finds disgusting?

Gulliver was disgusted by many of their actions, but their eating habits (and diet) were most disgusting of all.

Here we entered, and I saw three of those detestable creatures, which I first met after my landing, feeding upon roots, and the flesh of some animals, which I afterwards found to be that of asses and dogs, and now and then a cow, dead by accident or disease. They were all tied by the neck with strong withes fastened to a beam; they held their food between the claws of their fore feet, and tore it with their teeth.