If there's genuinely a Mad Cow Disease outbreak no one will want it and the point is moot, but I'll run with my scenario.
I think this is part of why China has cut off the UK and Ireland as well. If the US decides to embargo them as well, I'll probably adjust that section of the OP, because it's primarily speculation and I'm trying to get to the bottom of what's going on.
From what
@Voltekka was saying it sounds like beef is selling more cheaply, which would imply market glut in Brazil at the least.
Wiki talks about South American poverty; my premise is that the beef will sell in the rest of South America for roughly what it's selling for in Brazil (or possibly a little less) because Brazil does better economically than a lot of the countries surrounding it.
China putting an embargo on the UK and Ireland should mean that Europe is glutted with beef that would normally be sold to China, and if European markets are depressed (or there's really a Mad Cow outbreak) then they aren't going to take Brazil's extra beef.
That leaves Africa (super poor), India (don't eat beef), Japan (I think largely farms their own), Russia (largely farms their own), and Australia, which I admit I don't know much about.
TL;DR - The places that would take it no questions asked are poor and the places that would pay handsomely will ask questions.