Interesting. Most of our pastures run 50-80% mix of red and white clover. Never had fertility problems, never had bloat, never had abortions. It could be because it's a normal part of their forage that it doesn't cause a problem.
Hungry cows will bloat on legumes, except lespedeza, and it is a possible problem. I've watched the cows graze through areas og clover and on into straight grass. They don;t make a big deal over the clover, it's just something to eat. I used to be really concerned about it, but now, although I still keep an eye out for it, I don't worry about it.
We put 5 bred heifers that belonged to the vet in a field of nearly total red clover. Left them there somewhere around 5 months, I'ld have to check the dates to be sure. When we pulled them out they had started ignoring the clover and were eating the little grass (fescue) and the weeds rather then the clover. The clover was knee high when we pulled them and sent them home, the grass and weeds werre eaten to the ground.
Although it is recommended that pastures be no more then 30% clover, in our experience it isn't really all that critical if it's plentifull enough that it's not a special treat type of feed.
dun