Energy is essential for all body functions and milk production. Insufficient energy intake can cause weight loss, reduced milk yield, and health issues, while excess energy leads to obesity. Energy is obtained from carbohydrates like sugars and starches, fats, and fibers in roughages and concentrates. Fats provide over double the energy of carbohydrates and are also important for various bodily functions like temperature regulation and nutrient absorption, but they are more expensive. The energy from feeds is broken down within the animal into gross, digestible, metabolizable, and net energy available after heat production.