I doubt it, even though its a plant. Horses mainly eat grasses of various sorts and i don't think plam fronds come under that category. If your horse is eating them I recommend that you remove them from your horses reach. It could be harmfull.
Palm fronds are defined as compound leaves - large, divided leaves - of a palm tree.
Palms in the desert do in fact have fronds, and example is the Date palm
The palm tree has palm fronds.
They are called Palm Fronds.
You can use palm fronds to thatch,or cover, the roof of your hut.
Fronds.
Fronds
They harvested the palm fronds.
fertilizer, shelter and religious ceremonies
A coconut palm has fronds not branches.
The Aboriginals
leaves and palm fronds