What?
Why?
Ahem. Sorry, lets try to work with this.
Hi, i'm breeding rabbits
OK, this part is clear enough. Plenty of people do this for a variety of reasons. This part is clear.
and i a friend told me that their urine contains an important quantity of ammonia.
An important quantity? What does that mean? That there is a large quantity? That ammonia is important? For what purpose? Also, most mammalian urine contrains the chemical urea, which is broken down to ammonia by bacteria over time. It also contains other things that mammals excrete.
Can someone tell me how to extract ?
Why? First explain how you will collect it in quantity, rabbits aren't prone to donating on command, in a defined place. You'd have better luck with a domesticated animal, like a dog or a cat. Heck, humans are perfect, you can ask, and they'll comply. Unless the whole topic is gross, but what makes rabbits better subjects in that regard?