Nope. No idea how long the hemmhorraging takes. Donāt really care.
Finding a dead mouse beats having them reproducing in your trunk.
Feeding rehomed feral cats is your best bet for keeping them around & relatively cheap.
Just do not leave cat food out overnight.
Though, if your barn is already overrun, food left out during the day can attract mice too.
Damned if you do, damned if you donāt.
But putting catfood in a secure container when you leave is better than having your tack destroyed.
Do NOT believe anyone who tells you barncats should not be fed.
Theyāll hunt, but they need food too.
WTFruitbat is wrong with your BO?
Do they not understand mice can damage their infrastructure by chewing wires as well as holes in stalls?
Is a barn fire preferable to feeding a few cats?
And as mentioned, hanta virus is no joke.
Stoopid way to run (as you describe) a ācompetitive barnā 
Donāt use Tomcat bait.
Itās advertised āchild and pet resistantā but it will kill anything that eats a poisoned mouse.
Give your local predators - hawks, coyotes, fox - a chance.
Trust me, MI has black snakes. Getting one to take up residence in your barn⦠Not so easy.