In cattle, energy is essential for bodily functions and production processes like growth, lactation, and reproduction.Energy supplements can decrease forage intake, and mature or dormant forages may not meet the maintenance energy requirements for all classes of cattle, requiring supplementation.Carbohydrates and fats are the primary sources of energy, while protein contributes to a lesser extent.Fibrous carbohydrates found in forages and by-product feedstuffs vary in digestibility, while grains are easily digested and provide more energy.Forage digestibility affects total digestible nutrients (TDN), and producers can control forage maturity to increase digestibility.High-starch grains, fibrous byproducts, and fat sources are common energy feeds.Energy deficiency can lead to weight loss, decreased growth, reproductive failure, and impaired immune systems.