The motto of the Rio grande Nat. Forest (where I fish a lot) is "Land of many uses."

These uses include grazing of cattle and sheep in the summer months. The animals not only eat the grass, but erode the land by creating trails along the streams. When the cattle, especially, wear a trail down to a level of 10 inches or so, they make a new, parallel trail. I consider these effects from their presence to be negative.

On the other hand, the animals drop a lot of cow pies (don't know what the polite term is for sheep feces), that eventually, I imagine, end up in the streams holding trout, making the streams more fertile, just as streams flowing below town sewage plants are more fertile than the waters above the sewage plants.

My question is: What is your opinion of the relative benefit/harm that the cattle and sheep do to the trout?