I guess that is a hit or miss situation. It would depend on the severity of the abuse. If it were lack of proper food and water to where you can tell the horse is apparently starved then I would call local Animal Authorities. If it were something along the lines of literal lacerations and sores not being treated on a horse after a period of time, then yes I would. Or if it were apparent those sores were being made by the owner or other human then yes as well. 

I guess it all depends on personal limitation and restraint. But good article, thank you for posting.