On average, I don't think this diet is too rich.  But if the cows are getting the stalks, the hay, and the corn silage fed to them separately then the cows will select the most nutrient dense feed first (that's natural survival instinct) and she might be getting too much hay and/or silage that way.
Even if these are mixed together, if the stalks aren't processed enough they'll get sorted out and eaten later - so the cow gets different rations different parts of the day and this also isn't good on the rumen.