Today is
SEveral things
First the grass is in too little of pieces therefore causing impactation colic
Second grass is usually full of fertilizers and pesticides
Another problem is with mold. It might not be a big problem if you raked it up immediately after mowing and fed it to them, but if allowed to sit for a period of time, it will start to mold quickly. I've seen people do it and not have any problems, but I'm the type of person who would have a horse kill over immediately from it, so I don't take any chances.
Support - Contact / Log in to my account