|dc.description.abstract||Beef producers are looking to alternative feed sources due to competition for starch sources among ethanol and livestock producers and with human food needs. Limited research is available on blended by-product feeds as alternative sources of starch and protein for backgrounding cattle. Three trials were conducted to evaluate the performance and effect on rumen fermentation and nutrient digestibility in growing cattle fed blended by-product pellets (BP). Pellets were based on by-products from the oilseed and grain sectors and were formulated to be isonitrogenous (17.0% CP) and isocaloric (1.92 and 1.28 Mcal kg-1 NEm and NEg, respectively). In Trial 1, four pellets were evaluated. The pellets were formulated to be either high starch (HS 45% DM basis) or high fat (HF 8.8% DM basis) and either low or high in soluble protein (LSP 27% of CP; HSP 37% of CP DM basis). In Trial 2, only the two HF pellets were evaluated. In Trial 1, 300 cross-bred steers (320 ± 21.6 kg, mean ± SD) were randomly assigned to one of 25 pens and fed one of 5 diets in a completely randomized block design. The control diet consisted of 46.9% forage and 53.1% barley-based concentrate. The four treatment diets consisted of 48.4% forage and 51.6% BP (DM basis). All diets were formulated to 1.63 and 1.02 Mcal kg-1 NEm and NEg, respectively (DM basis). In Trial 2, 180 cross-bred steers (326 ± 20.3 kg, mean ± SD) were randomly assigned to one of 15 pens with each pen randomly assigned to one of three treatments in a completely randomized design. Treatments included a control diet consisted of 54.3% forage and 45.7% barley-based concentrate and the two HF BP treatment diets which consisted of 55.6% forage and 43.4% of one of the two HF BP used in Trial 1 (DM basis). In Trial 1, no (P>0.05) effect of treatment was observed on ADG, however, DMI was reduced (P<0.01) with the HS treatment relative to the control and HF treatment. No significant differences (P=0.16) were observed in DMI between steers fed the control and HF BP diets. Gain:feed (G:F) was the poorest (P<0.01) for the HF diets. In Trial 2, ADG was lower (P=0.04) and DMI was higher (P=0.04) for HF BP (Control vs. HF), therefore cattle fed the control diet had superior feed efficiency (P<0.01). Dietary NEg content (Mcal kg-1 DM) as calculated from animal performance was 7.5 and 8.3% lower (P<0.01) for cattle fed the HF diets relative to the control cattle in Trial 1 and 2, respectively. Trial 3 used 5 crossbred heifers (631 ± 31 kg, mean ± SD) in a Latin square design. Diets were the same as that used in Trial 1. Heifers fed HF BP had higher (P=0.05) mean pH values than those fed the control diet and trended (P=0.07) to have higher mean pH than those fed the HS BP. Feeding HF BP caused a decrease (P<0.05) in propionate concentration, without affecting acetate or total VFA concentration. Rumen ammonia-N levels and digestibility of CP was highest (P<0.05) for HS, intermediate for HF, and the lowest for the control. Feeding HF BP relative to both the control and HS diets reduced (P<0.05) GE, DE and EE digestibility. Total nitrogen excretion (% of total N excretion) was not affected (P>0.05) by treatment. Feed costs per kg of gain were reduced by feeding HF BP due to cost of ingredients and relative excellent cattle performance. These results indicate that BP are a viable and economic alternative for supplementing energy and protein in backgrounding diets with no adverse effects on rumen fermentation. Moreover, feeding BP does not increase the potential of having nutrient excretion issues in the environment.