For beef cattle, distillers grains can provide a viable source of supplemental protein, replace some corn as an energy source, and improve average daily gain and feed conversion, depending on how much distillers grains is included in the ration. However, feeding distillers grains creates some nutrition management challenges, in part because most of the nutrients in corn become three times more concentrated in distillers grains. Nutrients such as sulfur are often added during ethanol production and can occur at even higher concentrations. Formulating rations to accommodate the nutrient composition of distillers grains is further complicated by the significant variation in nutrient content that has been shown to occur between ethanol facilities and even between batches from the same facility. These nutrient issues can limit or even prohibit distillers grains use in some feeding situations.
Sulfur is the most likely nutrient to limit distillers grains use in beef production. Sulfur is a required macromineral for cattle, but ingesting too much can result in sulfur toxicity and reduce feed and water intake, and may cause polioencephalomalacia, a potentially fatal neurologic disease. Numerous analyses have shown that the sulfur content of distillers grains is generally four to seven times greater than that of corn. Further, the sulfur content of condensed distillers solubles, another ethanol co-product often mixed with distillers grains, can be up to 10 times that of corn. These high sulfur levels are especially problematic in areas with high sulfite levels in the water cattle drink and during seasons when water consumption is higher because of higher temperatures.
A second nutrient that can limit distillers grains use is fat. Distillers grains are an excellent source of energy for cattle, but too much total fat in rations can depress fiber intake and digestion. The fat levels reported for conventional distillers grains (8 to 13 percent) will generally limit distillers grains inclusion to about 50 percent to achieve acceptable growth performance.
A third nutrient of interest is phosphorus, which must be managed for both nutritional and environmental reasons. The nutritional concern is ensuring an appropriate ratio of calcium to phosphorus in rations. Because this ratio can be achieved by supplementing calcium, phosphorus generally is not considered a nutritionally limiting factor for distillers grains inclusion. The environmental concern is that higher phosphorus intake by cattle fed distillers grains results in greater phosphorus excretion, which may increase phosphorus run-off from feedlots and harm streams and rivers. In much of Iowa and other Corn Belt states that raise both corn and cattle, higher phosphorus excretion can be managed through appropriate manure distribution. However, phosphorus may be a limiting factor in feedlots in corn-importing regions with different soils types and environmental concerns.
Source: Roxanne Clemens, rclemens@iastate.edu, 515-294-8842