How to prevent runny stools on cows eating spring grass. When cows have the opportunity to get some dry matter with each bite of spring green grass, their rumen function is improved. Manure piles stack up perfectly and the cow's tails will be clean, not covered with runny manure. If you want to keep your farm profitable every year, check out my 3 grazing books that I wrote on our website: http://greenpasturesfarm.net/books/