By Mary Drewnoski

Corn residue is not only an outstanding forage resource for wintering cows, but also an option for backgrounding calves or growing heifers. Given the typical rental rates for corn residue and the cost of distillers grain, these two feed resources together make one of the lowest-cost growing rations.

To understand why distillers grain is such a good supplement for growing calves, you need to first understand a little about how protein is used in ruminant animals. In ruminant diets, not all protein is created equal, and this is particularly apparent for animals with high protein requirements, like growing calves.

Ruminally degradable protein is used by rumen microbes to grow (eventually, rumen microbes become a source of protein for the animal called bacterial crude protein). Ruminally degradable protein supplied in excess of the microbes' requirements cannot be used by the animal as a source of protein. When the animal's protein need is high, bacterial crude protein does not meet the animal's demand, so a source of ruminally undegradable (or bypass) protein is needed. In this scenario, providing more ruminally degradable protein will not help.

A good example of this concept is the comparison of urea as a source of protein versus distillers grain for growing calves grazing corn residue. Urea is 100% ruminally degradable, while the protein in distillers grain is only 37% ruminally degradable, meaning that 63% of the protein bypasses the rumen (is not degraded in the rumen) and can be absorbed and used as a source of protein for the animal itself. When a similar amount of energy (3.1 pounds of total digestible nutrients per day) and protein (0.9 pound of crude protein per day) were supplied by corn, plus 5% urea (4 pounds of dry matter per day) versus distillers grain (3 pounds DM per day), the gain of calves receiving distillers grain (1.32 pounds per day) was more than double that of the calves receiving the corn plus urea (0.53 pound per day). The difference in gain with urea and distillers grain emphasizes the value of bypass protein (or ruminally undegradable protein) for growing calves.

Distillers grain has consistently been the lowest-cost source of bypass protein in the Midwest. In addition, distillers grain is high in energy (greater than corn). So distillers grain makes an ideal supplement for calves grazing corn residue. A pooled analysis of several studies reported in the 2017 Beef Report illustrates the amount of distillers grain that would need to be fed to achieve various rates of gain. Its data suggests that for a targeted ADG of:

• 1.1 pounds per day, calves would need to be supplemented with 1.8 pounds of DM, which is 2 pounds of dry distillers, or 3.6 pounds of modified distillers

• 1.5 pounds per day, calves would need to be supplemented with 3.6 pounds of DM, which is 4 pounds of dry distillers, or 7.2 pounds of modified distillers

• 1.9 pounds per day, calves would need to be supplemented with 6 pounds of DM, which is 6.7 pounds of dry distillers, or 12 pounds of modified distillers

In forage-based systems, similar performance is observed with dry, modified and wet distillers grain as long as the same amount of dry matter is fed. It is important to note that the estimates are based off of calves being fed in a bunk. Feeding on the ground will increase waste and, thus, increase the amount of distillers grain needed. In trials evaluating the waste with ground feeding, 5% was measured for modified distillers, 20% for wet distillers and as much as 40% for dry distillers when compared to bunk feeding.

If you are looking to background calves or grow replacement heifers this winter, grazing corn residue and providing supplemental distillers may be a system worth considering.

Drewnoski is a Nebraska Extension beef systems specialist. This report comes from UNL BeefWatch.