Utilization of feed co-products from wet or dry milling for beef cattle.

Recent expansion of the ethanol industry has led to an increase in production of co-products that are used extensively in the cattle industry. A variety of different co-products are being produced, all with slightly different nutrient compositions. Maize [corn] gluten feed (CGF) is the main co-product of the wet milling industry, while distillers grains with solubles (DGS) is the main feed produced by dry milling plants. These co-products have little to no starch remaining, which reduces acidosis challenges in feedlot cattle and reduces negative associative effects of starch digestion on fibre digestion for cattle on high forage diets. The extent to which an ethanol plant dries these co-products affects their nutritional value. For feedlot cattle, wet DGS (WDGS) have a feeding value 30–40 percent greater than maize when included at 10–40 percent of diet DM. Modified and dried DGS have feeding values 15–30 percent and 13 percent greater than maize, respectively. Because feeding DGS results in improved cattle performance, cattle can be fed for fewer days resulting in decreased costs. Feeding high levels of DGS increases the sulphur content of diets and may decrease performance or result in polio encephalo malacia (PEM), particularly if sulphur levels exceed 0.47 percent of diet DM. Increasing roughage levels in the diet appears to be an effective way of minimizing sulphur impacts and maintaining cattle performance. In addition, lower quality roughages could be fed in feedlot diets containing WDGS without diminishing performance. Intense maize processing increases the value of diets containing CGF. However, greater performance responses have been seen with less intensely processed maize in diets containing DGS. There appear to be many complex interactions that cause these differences in performance, and warrant further study. The environmental impacts of these co-products are quite important. The ideal scenario for reducing greenhouse gas (GHG) emissions of ethanol involves feeding WDGS to feedlot cattle within 100 km of the ethanol plant. In this scenario, GHG emissions can be reduced by 56–62 percent compared with gasoline due to improved cattle performance and decreased energy costs at the ethanol plant when DGS is not dried. Feeding high levels of co-products increases nitrogen (N) and phosphorous (P) in the diet, which increases the N and P content of the manure. Capturing these nutrients in the manure and applying to crop land as fertilizer increases the value of the manure above the costs to apply it. These co-product feeds are an excellent source of energy, protein and P for cattle on high forage diets, and quadratic increases in average daily gain (ADG) and final bodyweight (BW) have been observed with increasing levels of DGS supplementation. Biofuel co-products as livestock feed – Opportunities and challenges 78 kernel to produce numerous products, some of which are intended for human use. Fresh water enters the milling system in the final stage of starch washing. Subsequently, it runs counter current with respect to the flow of maize, passing through numerous screens and separating implements, acquiring soluble nutrients at each step. Ultimately, this solution will serve as the resource to steep the maize as the initial step in the process. Lactic acid-producing bacteria in the steeping process ferment the soluble carbohydrates collected by the water to further kernel softening. Following the steeping process (Figure 1), maize kernels are separated into kernel components of maize bran, starch, maize gluten meal (high in protein), germ and soluble components. If the wet milling plant is fermenting starch into ethanol, a portion of the steep water (now called steep liquor) is added to the fermentation vats to supply nutrients for the ethanol-producing yeast cells to grow. The ethanol is distilled off after the fermentation process. The solution exiting the still is called distillers solubles, not to be confused with dry milling distillers solubles. This product contains very little maize residue, almost no fat, and is high in protein from the remnants of yeast cells from the fermentation process. The distillers solubles and a portion of the steep liquor are added to the bran fraction of the maize resulting in WCGF. The WCGF can have a portion of the germ meal added if the plant has those capabilities. For a more complete review of the wet milling process, please refer to Blanchard (1992). The actual composition of WCGF can vary depending on the plant capabilities. Steep, a combination of steep liquor and distillers solubles, contains more energy (136 percent the feeding value of maize) and protein than maize bran or germ meal (Scott et al., 1997). Therefore, plants that apply more steep to maize bran or germ meal will produce WCGF that is higher in crude protein (CP) and energy. For instance, Sweet BranTM is a trademarked WCGF product that Cargill produces. This product contains more steep and germ meal than other WCGF, causing it to have a higher energy value (112 percent the feeding value of maize). Wet CGF contains 16 to 23 percent CP, of which about 70 percent is degraded in the rumen (degradable intake protein, DIP) and used by rumen microbes. During wet milling, maize gluten meal is removed and marketed in higher value markets. Maize gluten meal should not be confused with WCGF because they are different products. Maize gluten meal contains approximately 60 percent CP of which 40 percent is DIP and 60 percent is bypass protein (also known as undegradable intake protein, UIP). Dry milling The dry milling ethanol process (Figure 2) is relatively simple. Maize (or another starch source such as sorghum [milo]) is ground and then the starch source is converted to ethanol and CO2 (fermentation). Approximately one-third of the dry matter (DM) remains as a feed product following starch fermentation, assuming the starch source is approximately two-thirds starch. As a result, all the nutrients are concentrated three-fold, because most grains contain approximately two-thirds starch. For example, if maize is 4 percent fat, the DGS will contain approximately 12 percent fat. • WDGS has a feeding value 30–40 percent greater than maize when included at 10–40 percent of diet DM. • MDGS has a feeding value 15–30 percent greater than maize when included at 10–40 percent of diet DM. • DDGS has a feeding value 13 percent greater than maize when included at 20–40 percent of diet DM. • High inclusions of DGS increase the sulphur content of diets, which results in reduced DMI and ADG, but has little effect on efficiency. • Feeding WDGS to feedlot cattle located close to an ethanol plant reduces GHG emissions 56–62 percent compared with gasoline. • Distillers grains are an excellent supplement for cattle on high-forage diets because of the high energy, protein and P contents, and lack of starch. MAIN MESSAGES