What do the cows feed on?

In late spring, summer and early autumn when pasture is plentiful and the weather is relatively good then our farmers put their herds out to feed on their lush grass, as it is the best nature can offer.  At other times of year when the grass is not growing and the weather is harsher cows tend to live indoors and will be fed on silage (grass cut in the summer and stored under wraps to preserve the essential nutrients) and other grass or vegetation based feedstuffs that keep the cows energy and nutrient levels up so they can keep producing milk in the dark, cold winter months.