jphone: I think what he really meant was the amount of time a horse breathes a certain number of breaths, which is the opposite of what you said.
Example 1: How long does it take a horse to breathe x times? Then that would be y amount of time of sleeping.
Example 2: How many times does a horse breathe in x amount of time? Irrelevant. How does that determine how long a person has to sleep for?