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Over the last decade, intensified ethanol production resulting in increased availability of distiller’s grains with solubles (DGS) in the United States has led to considerable research on the effects of DGS on beef feedlot performance and carcass quality.
Gordon et al. (2002) reported increased DMI, ADG and feed efficiency in heifers fed finishing diets with inclusion of dried DGS (DDGS) at 50% of the diet while Pingel and Trenkle (2006) reported that DDGS have a higher relative feed value than corn when included at 20% of the diet. Greater performance is likely due to increased fiber digestion and oil content of the by-product. Whereas corn grains have relatively high starch content, DDGS have little starch remaining, leaving a highly fermentable carbohydrate source. However, increasing the DDGS fraction of the diet not only reduces total dietary starch intake, but it also has resulted in decreased digestibility of starch derived from other ingredients (i.e. corn; Pingel and Trenkle, 2006). Although feeding higher levels of DDGS apparently does not significantly affect live animal performance in the feedlot, their effects on carcass composition are still in question.
Increased yield grade has been reported with inclusion of DGS in the diet, regardless of level, while marbling score does not appear to be affected until DGS inclusion rates exceed 30% (Corah and McCully, 2006). This may be due to a reduction in starch content which can affect adipocyte proliferation and differentiation which can ultimately influence marbling score (Smith and Crouse, 1984). However, it has not been determined if level of dietary CP influences marbling through decreased energetic efficiency, or if dietary fat decreases performance in DMI and digestibility. Therefore, our objective was to evaluate the effects of dietary fat and crude protein on feedlot performance, carcass characteristics, meat quality and circulating concentrations of metabolites and hormones associated with nutrient utilization in finishing steers fed differing levels of DDGS.
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