You're not a real government agency until you have an intelligence branch. The Department of Agriculture gets funding in defense bills (because, ahem, America gets angry when our cows get mad).

Seriously, though, there are something like two dozen intelligence services [edit: Wiki says 16 big ones] in the US federal government.

the Washington Post had a fantastic series which tried to get a handle on the complexity of the intelligence services operating in America today: http://projects.washingtonpost.com/top-secret-america/articl...

here's the leader:

The top-secret world the government created in response to the terrorist attacks of Sept. 11, 2001, has become so large, so unwieldy and so secretive that no one knows how much money it costs, how many people it employs, how many programs exist within it or exactly how many agencies do the same work.

It's a harrowing read.

Ag stats are pretty sensitive.

I would bet that the animal pathology work they do is more sensitive.

Honestly, I don't think the FBI has the expertise they'd need to slip in a backdoor which goes for this long without being found.