Corn is normally fed as the main source of fermentable energy. The energy is primarily in the form of starch, where the rate of digestion is very much dependent on how finely it has been ground or how it has been processed.
Some farmers may be looking at replacing some or all of the corn in the diet. There are several by-products that can be used to partially replace corn grain in the diets. Some of these primary by-products include hominy feed, soybean hulls, molasses, brewers grain or distillers grain. The energy in many of these by-products mentioned is primarily in the form of digestible fiber. However, there are some by-products which contain processed carbohydrates and sugar and they should be handled differently in the ration.
Another source of energy is to feed fat products which include whole cottonseed, whole soybeans, tallow, animal fats or inert fat supplements. However, it is important to limit the total amount of fat in the diet when multiple fat products are fed to avoid any negative effects on fiber digestion, animal health and milk-fat depression. The amount of corn that can be replaced by these fat products will very much depend on the quality and type of forage fed, production level, and feeding system constraints.
In recent times, distillers grain have receive a lot of attention as it is the primary by-product from the production of ethanol. However, the nutrient content of distillers grain will have a wide range of variation. Hence, some plants have taken extra efforts to produce a more consistent product and typically collect a premium for their distiller's grain.
Recent studies have showed that distillers grain can provide up to 40% of total ration DM, but that is not practical for most dairies. This is mainly because distiller's grain contain high levels of phosphorus. Like other by-product feeds that contain higher concentrations of phosphorus, high feed rates increase the amount of phosphorus in the manure which builds up in the soil. Long term effects include lower applications rate of manure to land and limitations on herd expansion without purchasing additional land.