Are you mowing your pastures with a lawn mower or a tractor with a brush hog mower? If you mow close enough to leave clippings in a row there is a chance it will mold and your horses may eat it. A mowed pasture looks great but be careful or your horses may colic. I have personally known of horses eating grass clippings and then die a painful death.
Not trying to scare you but be watchful.
I'm mowing with the lawnmower. Yes, there are lots of cuttings left, but they are the cuttings of the weeds they don't want to eat living, and they seem to avoid them cut also. They've been grazing where I haven't mowed yet. The clippings are thick in spots, but I kick and spread them. Thinking of resting the pasture awhile now anyhow, untill it rains and can grow up a bit.