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The objective of this experiment was to determine the effects of supplemental fat from either dried distillers grains with solubles (DDGS) or raw corn oil on the digestibility of nutrients and long chain fatty acids. When compared to corn grain and grass hay, DDGS have considerably greater levels of fat, which may negatively influence rumen microbes and nutrient digestibility. Six medium‐framed crossbred steers (initial BW = 602 ± 23.6 lb) were used in a Latin square design to determine apparent total tract digestibility of diets formulated with no supplemental fat or supplemental fat from either DDGS or raw corn oil. Steers were randomly assigned to of 1 of 3 dietary treatments: 1) supplemental fat from DDGS (DG); 2) supplemental fat from corn oil (OIL); 3) no supplemental fat (NO OIL; Table 1). The DG treatment was comprised solely of dried distillers grains with solubles (DDGS). The OIL treatment was comprised of a combination of high‐protein dried distillers grains (HP DDG), corn bran, and corn oil formulated to be isonitrogenous and isolipid to the DG treatment. The final dietary treatment (NO OIL) was a combination of HP DDG and corn bran formulated to be isonitrogenous to the DG and OIL treatments, but with no additional fat. Treatment diets were administered over 3 consecutive 19 d feeding periods that consisted of 14 d diet adaptation followed by 5 d total collection. No differences were observed for DM, OM, ADF, NDF, or N, digestibility. Ether extract digestibility was lower in NO OIL compared to DG and OIL. Apparent digestibility of C17:0 was the lowest for OIL and greatest for DG; NO OIL was intermediate but different from both DG and OIL. C18:0 apparent digestibility was greatest for DG, lowest for OIL; NO OIL was intermediate but not different from either DG and OIL. C18:1c9 digestibility was greatest for DG, intermediate for OIL and least for NO OIL. Apparent digestibility of C20:3, C20:5, C22:2, total C20, and total conjugated linoleic acid were greater in DG and OIL than in NO OIL. These results suggest that providing low concentrations of supplemental fat as either DDGS or raw corn oil to growing steers on high forage diets will not influence digestibilities of DM, OM, ADF, NDF, or N. Digestibilities of ether extract and certain FA are affected by fat inclusion. Low levels of supplemental fat from either DDGS or corn oil may be included in high‐forage rations fed to growing beef steers with no adverse affects on digestibility of nutrients or FA.

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