@Scribbler well, sure–every company that comes out with fly spray doesn’t need to demonstrate that permethrin is effective. But if they’re making claims about duration, like Endure is, they’ll have to back that up, since that really has nothing to do with the repellent. For Endure it’s “RepeLock”…whatever that is. Something that binds to the hair. And their claim is it provides up to 14 days of “fly protection” not that it’s just present for 14 days. From the Farnam site:
“Provides up to 14 days fly control”
and
“Application should be liberal for best results. Reapply every 5 to 7 days under normal conditions for initial applications. As protection builds, reapply every 10 to 14 days as needed. Also, reapply each time animal is washed or exposed to heavy rain.”
And, interestingly:
“Repeat application as necessary but no more often than once every 5 to 7 days.”
(I can tell you that when I used Endure, I applied it a hell of a lot more frequently than 5 - 7 days! Because it sure didn’t last that long :lol: But I also found it to dry the coat terribly, which is maybe why they say not to use it with any frequency?)
But someone…presumably Farnam, because I don’t think they purchased the formula?..would have had to do some testing to support those claims. IIRC from the launch of Endure, it was lab testing much like vxf is talking about. Unfortunately that doesn’t translate well to real life 
Also kind of interesting is Endure’s active ingredient list:
[TABLE=“border: 1, cellpadding: 3, cellspacing: 0”]
[TR]
[TD=“align: left”]Cypermethrin, CAS # 52315-07-8[/TD]
[TD=“align: left”]0.15%[/TD]
[/TR]
[TR]
[TD=“align: left”]Pyrethrins, CAS # 8003-34-7[/TD]
[TD=“align: left”]0.20%[/TD]
[/TR]
[TR]
[TD=“align: left”]Piperonyl Butoxide Technical*, CAS # 51-03-6[/TD]
[TD=“align: left”]1.60%[/TD]
[/TR]
[TR]
[TD=“align: left”]Butoxy Polypropylene Glycol, CAS # 9003-13-8[/TD]
[TD=“align: left”]5.00%[/TD]
[/TR]
[/TABLE]
I don’t think I’ve seen another with cypermethrin?
Another thing of note…the aerosol Pyranha contains 0.3% pyrethrin. I’ve always heard people swear by it but never understood the hype. Oh, it’s got THREE TIMES the pyrethrin of the standard spray Pyranha. :lol: No wonder!!!