Did you read the article at all? Because according to that site, they are being bled for medical products, namely serum from the blood, not for medical tests. So those horses' blood is being used to treat humans. Like ES said, humans should and do come first.
And should it be the case that this is what is really going on (it says the video was taken by PETA, who are a group of nut jobs if you ask me) then I would hazard a guess that the rest of the horse is being used in some way too - meat, leather, glue etc.
There is ALWAYS three versions of the truth, and every thing you read on the internet should be taken as opinion rather than hard and fast facts.