October 2012

photo of ear of cornCorn harvested this fall may have lower test weights than commonly observed by crop producers. Light test weight corn is often discounted in price leading both cattle feeders and farmers to wonder about its feed value. Research results have shown the feed value of light test weight corn when it is used in various cattle rations.

Test weight (TW) in corn is a measure of density (weight per unit volume) with the current standard at 56 lb/bu. Many stress factors can contribute to lower test weight corn: hybrid, temperature, solar radiation, hail, early freeze, disease, and drought. The result of a reduced growing season is grain with higher protein, fiber, and mineral concentrations. The greater concentrations of these nutrients come at the expense of reduced starch content, the primary fraction used for energy when grain is fed to livestock. Some areas have experience feeding light test corn because of drought or a shorter growing season (cool temperatures) in the past. The current drought situation has made this a concern for a large portion of the Corn Belt.

Anecdotal evidence from previous closeouts of cattle suggests that when light TW corn is fed cattle performance (feed efficiency) becomes poorer. However, data based on more than 50 years of research suggests there may not be a large reduction in feed efficiency when light TW corn is used. When compared on a dry weight basis, the feeding value is often similar for light and normal TW corn. The majority of feeding studies conducted agree with these observations.

Several feeding experiments have evaluated the feeding value of light test weight corn. Beef cattle research conducted at UNL and NDSU in growing diets or forage based diets have slightly different outcomes but both show no negative impact on performance. At UNL, two years of performance data suggests that there is no difference in performance between light (46.8 lb/bu) and normal (56.2 lb/bu) TW corn. At NDSU, data suggests that when light TW (39.1 lb/bu) corn replaced 0, 33, 67 or 100% of the normal (56.0 lb/bu) corn there was an improvement in feed efficiency. The authors noted that as grain with a lighter TW was included in the diet, the negative associative effects of ruminal starch digestion on fiber utilization was reduced. In either study, the feeding value of light TW corn is similar to slightly improved compared with normal corn. Corn producers that grow calves on a high forage diet may be able to capture the value of the corn if feed mills or ethanol plants discount low test grain.

Finishing research conducted at UNL and NDSU with low TW corn shows a slightly different response. At UNL, the same corn TW that were fed in the growing study was fed to finishing steers. The combined data from two years suggested a slight improvement in feeding value for light TW corn. However, when light (39.1 lbs/bu), medium (46.9 lbs/bu), and normal (53.7 lbs/bu) corn were fed at NDSU there was a decrease in performance as TW decreased. It appears that when corn grain has a TW lower that 45 lbs/bu, finishing performance may be reduced. This suggests that the grain may be discounted using a similar structure that local elevators or ethanol plants are using when purchasing grain.

Matt Luebbe
Feedlot Nutrition and Management Specialist
Panhandle Research and Extension Center
University of Nebraska–Lincoln