Advancing biofuel processing technology continues to change the nutrients content of the maize co-product feed ingredients available in the USA, with possible implications for exported distillers dried grains with solubles (DDGS). Use of corn-based DDGS in domestic swine feeds still is expanding and is increasingly attractive in many markets abroad. Its use in poultry feeds is growing, tooparticularly for turkeys and layers in the American Midwest where most corn and ethanol production is located. However, at least one large broiler chicken integrator, Perdue Farms, which is also in the grain supply business, plans to build an ethanol plant on the USA's eastern coast.

The 'ethanol boom' is fueling increased diversity and specialisation of DDGS as well as other corn co-product ingredients, Dr Jerry Shurson, a swine nutritionist and specialist in DDGS at the University of Minnesota, reported recently: "Practicing nutritionists formulating monogastric diets have to pay particular attention to the new high-protein products, which have lower energy and phosphorus values. While typical ethanol-DDGS remains attractive for pigs and poultry, a closer look at high-protein DDGS, glutenol, and CPC (corn processing co-product) in least-cost formulated swine diets suggests these ingredients may be more useful in ruminant diets."

While Dr Shurson's comments relate mainly to the corn ethanol co-product situation in the USA, foreign buyers also may want to keep track of the nutrient profiles of dynamic DDGS available in international markets.

Pigs: "Excellent results" with 10% DDGS

"Currently," Dr Shurson notes, "North American pork producers are achieving excellent results with high-quality, gold-coloured corn DDGS at inclusion rates of 10% in a range of diets."

He points to Minnesota studies which show the maximum recommended dietary inclusion rates of ‘golden' DDGS as: Gestation 50%; lactation 20%; post-weaning (with pigs weighing more than 7 kg) 25%; and, grow-finish 20%. However, he suggests, by formulating diets on a digestible amino acid basis and using other protein sources high in threonine, formulators can maintain growth rates on grow-finish diets with inclusion of high-quality DDGS up to 30%. He adds that adding golden DDGS plus phytase to swine diets can reduce phosphorus excretion dramatically. For details, see MNC8-11.pdf.

Now, however, the new technology to enhance yields in dry-grind ethanol plants is changing the mix of co-products, Dr Shurson notes: "New enzyme applications are increasing the crude protein content of DDGS, removing the germ or bran from corn prior to fermentation, and removing phosphorus prior to producing DDGS. These changes in ethanol processing also may have the effect of reducing the resulting co-products' nutritional and economic value in monogastric diets."


Higher protein from newer plants

As crude protein increases, Dr Shurson points out, other nutrients in DDGS must decrease in concentration. He notes that one company's branded high-protein DDGS product has 34% more protein than the company's standard-branded DDGS (see table Comparing DDGS products').

"Much of this increase in crude protein content is at the expense of fat (59% reduction) and phosphorus (42% reduction). In fact, the relative proportion of nutrients in the high-protein DDGS is similar to that found in distillers dried grains (DDG). Although high-protein DDGS has less neutral detergent fibre (NDF), the reduction in fat content is likely to substantially reduce the energy value for swine and poultry.

"Moreover, roughly 50% of the diet cost savings of using DDGS in swine diets results from lower levels of inorganic phosphorus supplementation. So, the much lower phosphorus content of high-protein DDGS may make it more difficult to achieve the same degree of diet cost savings as provided by 'typical' DDGS."

Other corn co-products that emerge from newer dry-grind ethanol plants include glutenol and CPC. Dr Shurson points out that both these feed ingredients have higher crude protein content than typical DDGS, but their concentration of lysine and other amino acids are not proportionately higher: "The high crude protein:lysine ratio may even reduce energy utilisation in monogastrics because of the additional energy needed by the animal to remove excess nitrogen."

Using nutrient content assumptions based on their previous work, Dr Shurson and colleagues in Minnesota formulated typical swine grower diets in order to demonstrate the importance of knowing the source of DDGS, having accurate DDGS nutrient specifications, and understanding how nutrient specifications can affect the opportunity cost for DDGS.

Dr Shurson emphasises that for all distillers corn co-products, metabolisable energy content, amino acid levels and digestibilities, and available phosphorus content are the primary factors that influence their suitability for use in swine and poultry diets: "These factors directly influence the economic value of DDGS and related co-products in their increasingly diverse forms. Based on our assumptions for energy value, the high-protein DDGS, CPC, and glutenol co-products have much higher value for ruminants because of the higher levels of nitrogen as CP and lower levels of fat and phosphorus."