Mallenders and salenders (sp?)?

[merry mischief]

What are they? Google seems to not have much on them?
Does this look like one?

 

[Black_Horse_White]

It's normally grease behind the knee and heel, the grease sticks to the skin and causes sores and scabs. My horse has in and it doesn't look like that.

 

[Black_Horse_White]

Also very scurfy, I use I fine tooth comb to gently remove it.