I don't know a lot about jennies, I don't have any but have had a couple here to "try" to breed to my jack.
From what I've heard, been told....... a jenny's heat is shorter than a mares. They will "chew" the air when in heat, much like a young horse will do when approaching an older herd memeber.
I do know jennys are generally quite forceful when in heat too. They will back a jack into the corner. The one experienced jenny I had here backed poor Kilroy into a corner and he didn't know how to accept that. My friend said when her jennies are in heat, they have actually backed gelding donkeys into corners and forced them to breed them.
Hi there...my jennys definitely chew in the air and they also make a BIG deal when they pee. They get their back legs spread wide...BIG tail arched in the air and look around to see if my jack is watching...it is quite a show lol! After she is done peeing the jack will kinda strut on over...smell the pee...then it looks as though he prays to the heavens (you'll know what I am saying) then he pee's over the spot that the jenny just pee'd in and if he smells that she is ready...she is usually nearby waiting. Jenny's are not shy and can be sexually aggressive as mentioned. LOL...I can't imagine having all jenny's in heat all the time...talk about hormonal teenagers