Using poultice and mud to relieve and protect itching horses

Penny and Cleo have reacted badly - I suspect - to the paspalum grass. Cleo also gets bad Queensland itch aka sweet itch and suffers from allergies to neck thread worms.
There's an awful lot of ticks on the property, but these two girls are doing ok with the ticks.
Due to scratching their itchy legs, they've caused some scabs and bleeding in places. I use an insecticide on them regularly, but it's not enough. So hoping the poultice and mud. The mud contains clay and really sticks to the skin. We use it on our greyhound and it's protected her skin from sunburn and drying out.