Can anyone tell me how long the donkey's period of heat continues .

I have learned from the following website ( Chapter 5: Horses, donkeys and mules ) that it recurs every 2-3 weeks but I am wondering how long this cycle (heat itself lasts 2-7 days apparently) repeats itself if the jenny does not become pregnant.

Does the cycle repeat until the end of the summer or does it go on for a few months?

Obviously it will stop when she becomes pregnant -which is what I am trying to prevent for now.