So what if it does ? They are in the horse trailer, not like they are going anywhere.
Also, its a waste of money, will do nothing for your power, and just annoy the rest of us on the road. Opening the exhaust without changing anything else will do little to nothing. Opening the exhaust with doing other things will only help at the upper RPM range. The adds and magazine BS you are reading is just that BS. Yes it will give you a few more horsepower if you lessen the back pressure. But you will only gain that horse power at near redline RPM. When was the last time you drove around your horse trailer at 5000 rpm ? Save your money for other things that are actually useful.