Generally, cows should be supplemented with corn in small amounts (0.25% of body weight or less). The objective of supplementation is to improve the energy intake of the cattle. Generally, this system is best used when forages are readily available, but the quality of the forage is insufficient to meet the nutritional demands of the cowherd. Depending on the quality of the forage, producers in this situation may be better off using a protein supplement, specifically degradable intake protein, which will increase forage intake and digestibility. Another alternative would be to use a fibrous energy source such as wheat middlings, distillers grains, corn gluten feed, or soybean hulls, which will provide energy in the form of highly digestible fiber, thereby maintaining forage utilization at or near maximal levels and no reduction in forage digestibility.

However, corn may also be used as a source of energy and would substitute the energy provided by the forage. As discussed previously, increasing the level of corn in the diet results in a reduction in forage intake and digestibility. Substitution takes advantage of that phenomenon and is most applicable when forage resources are limited, or simply too costly, and grain is cheap. The amount of forage that can be replaced by a pound of corn depends on the quality of the forage. Generally, substitution rates will range from 1 pound of corn to 1.5 pounds of alfalfa or high-quality hay up to 1.9 pounds of poor-quality prairie hay. The amount of corn that should be fed depends on the forage quality and quantity and the nutrient requirements of the cowherd. Also, any time cattle are fed relatively high levels of corn, there is a risk of digestive disturbances (acidosis, bloat, and founder). Providing adequate bunk space, feeding at the same time each day, and inclusion of an ionophore will help minimize the risk of these disturbances.