why is my rabbits hay smelling so bad

hi everyone, I have a rabbit that is one year old, she is an outdoor rabbit and at night it as been getting in the 30s here, my hutch has a wire floor so i have mats and I put hay on the bottom so she can stay warm and off the wire. I clean her pee and poop tray, put fresh hay in there and cover the hutch at night so she wont get cold. and in the morning I have to change all the hay and put new hay cuz the hay is starting to smell really bad, it smells like a sweaty armpit and I don't know why and im not sure if it is her pee or her hay. would this be normal for her pee to smell like this. I give her timothy hey. what should I do about this. thanks

The hay could be old or moldy. Could you attach a picture? Hay shouldn't smell like armpits

It shouldn't smell bad.

Hm, mine have a huge hay rack, I have no idea how they can tell yesterdays hay from todays, it comes from the same bale and barn. Nevertheless, I only fill one half of the rack with new hay, that's the half that gets munched of, the other, one-day-spent-in-the-rack stays untouched. No turning or mixing changes that. Interesting, but somewhat annoying.

Oh, I put that wasted hay in the garden the next day, where it is yummy again, picky critters...