It’s a bit more complicated than just providing an number of calories. Calories are not the common way that farmers and animal nutritionists only measure nutrition intake for dairy cattle. Depending on where the cow is in her life, she requires different nutritional needs.
Nutritionists focus on the net energy that comes from different feeds to determine the best needs for the cow and pounds of feed.
Not all the feed that a cow consumes turns directly into energy. Some of it is wasted and some won’t always be digested properly. So, net energy is the actual amount of energy that the animal uses. So farmers use a lot of different ways to determine the energy of feed. Each type of forage or feed is analyzed at a lab to determine how much energy it would give the animal. The net energies are always changing because they are dependent on the type of forage of course, but also the growing conditions, age of the field, and when the field was cut. For example, a carbohydrate is a type of energy.
Think about it like the nutrition table on food you eat. Just looking at one component isn’t an effective way of determining the healthiness or nutritional benefits of that product. You need to look at everything in the product and how much energy it will give you.
Learn about specific things dairy cows eat.
Generally speaking, a lactating cow will consume between 18 and 25 kg of dietary dry matter, or about 100 pounds of all feed, each day.