Initially, the pride and temperament were only going down if the girl was in the barn with a cow rank below B+. I don't know if something has been altered in the code, but a S+ cow should never go broken : what you describe ("if you put in the time and effort a slave thats happy to be a cow should be the reward") was precisely the mecanism which was wanted when conceiving the original mod.
B+ and A+ cows are loosing nature and temperament in the barn, S+ don't though, which is fine imo
And if impregnation is done via the 30 or 60 spark option there is no stat loss but if the slaver is doing it, the cow is loosing 1 nature and temperament (down until broken) which is then unintenional i suppose
and I realized that endurance loss settles at weakend which isn't as bad as I first thought. Though, it would be nice to have an easier way to maintain max endurance for maximizing milk production. Maybe even just a barn option for workout, just so that I don't have to shuffel my slaves forth and back every few days in order to have my cow do acrobatics^^
Anyways, the barn is fun and I'm looking forward to other side buisnesses. I like the possibility to keep some slaves I grew fond of, not having to sell them (a personal harem would be nice too)
With respect to that, I also wouldn't mind some kind of bonus for no neoplasty (or remove the neoplasty option) so that certain slaves (e.g. nice image + exquisite beauty) are kind of a rare catch which I'd want to keep for myself and which I'd want to train even if other stats suck.