How did master houyhnhnm react when he learnt about the ill treatment to horses in gulliver's travels

As one might expect, the Master Houyhnym (known as Mistress), is appalled at the idea that one might see horses as nothing more than pack animals, or something that is simply used for the pleasure of mankind. Mistress believes that the horses should be respected because it is her experience that the humans (the Yahoos) are actually the ones who are the most despicable.