Forage Sorghum Silage as an Alternative to Corn Silage

Corn silage is the preferred roughage source in diets for growing and finishing cattle across the United States. Corn silage couples a roughage and starch component, making a high-yielding and energy-dense feedstuff for feedlot cattle. Traditional feedlot diets are grain-based, but contain minimal roughages that are largely to promote energy intake and maintain proper rumen function. Roughages can be provided in a variety of forms, from more common forage crops, such as corn silage and alfalfa hay, to co-product feeds such as wheat straw and corn stover, sometimes referred to as "alternative" sources of roughage. Many alternative sources of roughage can be utilized in feedlot diets when balancing on an equal neutral detergent fiber basis (NDF) to account for differences in energy density of the forages. Alternative forage sources growing in popularity are varieties of sorghum. Despite the overwhelming preference for corn silage as a roughage source, the cost of seed, nitrogen, and harvesting makes corn silage production very expensive. Forage sorghum is one sorghum variety that represents a low-cost alternative to corn silage and has been gaining popularity due to its improved drought resistance and adequate forage yield. With the proper diet formulation, less forage sorghum (on a DM basis) is required to replace corn silage as a roughage source. Researchers at Penn State wanted to evaluate how cattle fed grain-based diets would perform in the feedlot and on the rail when fed forage sorghum silage as a roughage source compared to corn silage.

Crossbred beef × dairy steers and heifers were sorted into three groups and fed treatment diets that differed only in roughage source. Diets contained either corn silage at 20% DM basis, forage sorghum at 11% DM basis, or a blend of corn silage at 10% DM basis and forage sorghum silage at 5.5% DM basis. These diets were based on dry-rolled corn and were balanced on an equal NDF and CP basis. Particle size was determined based on the Penn State Particle Size Separator method (Figure 1). The forage sorghum in this study was harvested and processed in a way that represents standard practices here in Pennsylvania and, briefly, was cut, baled, and wrapped in individually fermented bales, which were then ground in a vertical screw mixer (~45 minutes) before being mixed into a total mixed ration (TMR). The corn silage was chopped and stored in a bunker silo. These processing differences resulted in differences in particle size that may have contributed to the findings in this study (Figure 2). The cattle were fed twice daily for ad libitum intake and fed to a common final body weight of 1500 and 1400 lbs for steers and heifers, respectively.

Ultimately, the cattle that were fed forage sorghum silage as both the sole source of roughage and blended with corn silage had an 8% greater DMI compared with the cattle fed corn silage as the sole source of roughage. The cattle fed diets containing forage sorghum also had a gain of 3.96 lbs/day compared with the 3.78 lbs/day gain in the cattle fed corn silage as the source of roughage. Corn silage on an equal DM basis has a greater energy density than forage sorghum, however, by balancing on an equal NDF basis eliminates this confounding factor and provides a more accurate basis for comparing these two sources of roughage in a feedlot diet. The reduction in intake when cattle were fed corn silage is likely due to the increased energy density of that forage. Because of this, the cattle that were fed forage sorghum as a roughage source ate more dry matter to consume equal amounts of energy as the cattle fed corn silage as a roughage source. While cattle fed forage sorghum ate a little bit more and gained a little bit more than cattle fed corn silage, ultimately, the F:G did not differ. It is possible that particle size (Figure 2) buffered the rumen more in cattle fed forage sorghum compared to cattle fed corn silage, however, additional research would be needed to test this theory.

Over the 120-day feeding period, on a per head basis, the cattle fed forage sorghum as a source of roughage consumed an additional 265 lbs of DM compared with the cattle fed corn silage as a roughage source. Cost of gain (COG) was calculated using production cost estimates from the Penn State Agronomy Guide for corn silage and forage sorghum silage, and commodity prices during the trial. On feed costs alone, the COG for the corn silage diet was $0.75 / lb of gain, while the forage sorghum silage diet was $0.77 / lb of gain. Cost of gain in this scenario is dependent on many factors, such as silage yields, silage DM, and the price of corn grain. However, forage sorghum silage offers other cost-saving potential compared to corn silage through alternative harvesting methods.

Despite the differences in feedlot performance, there were no differences in any of the carcass characteristics evaluated, nor were there differences in the distribution of yield and quality grade. These data are important for cattle feeders who choose to market in programs where price is determined by carcass characteristics (i.e., grid or formula pricing). 

Results from this study show that replacing corn silage with forage sorghum silage as a roughage source in feedlot diets may increase DMI and ADG. However, the main drivers of cattle feeding profitability, feed efficiency, and carcass quality were unaffected by roughage source. Cost savings are highly dependent on factors such as forage DM yield, commodity prices, and farm-specific factors. Regardless of cost, forage sorghum may replace some or all of the corn silage in a feedlot diet when balanced on an equal NDF basis.

Tables and Figures

¹Contains (DM basis) 22.60% Ca (CaCO₃), 17.40% NaCl, 5.20% Mg (MnSO₄), 3.50% K (KCl), 1,000 mg/kg Zn (ZnSO₄), 180 mg/kg Cu (CuSO₄), 19 mg/kg Se (Na₂SeO₃), 35,500.5 IU/lb. Vitamin A, 1,477.1 g/tonne monensin.

²All values reported (other than DM) on a % DM basis.

Published first in Keystone Cattlemen's.