I'm not a veterinarian, nor a farmer, but i seem to remember my dad saying moldy hay negatively effected cattle weight gain and general health. I do gather mushrooms to eat, and seems like there is quite a bit of caution about eating the wrong ones, are cattle immune to "bad" mushrooms?Heck the cows will eat it and the mushrooms certainly don't care. That's the chance we take every time we cut, danged if you do and danged if you don't.