They are alot of products on the market for that. Show sheen and I think the mane and tail brand did one for frizz. I would try wetting it down and brushing, Also it would work best if you got a spray on detangeler, or mixed some condioner and water in a spray bottle. My Mini's hair was very frizzy, And then I discorvered that under his mane was matted. Also, to help a horses mane lay on the right side and stay down and less frizzy I brand the mane in small sections. Your horse is beautiful besides that.