Digestibility and performance of steers fed low-quality crop residues treated with calcium oxide to partially replace corn in distillers grains finishing diets.

Two studies were conducted to identify methods for treating crop residues to improve digestibility and value in finishing diets based on corn grain and corn wet distillers grain with solubles (WDGS). In Exp. 1, 336 yearling steers (initial BW 356 ± 11.5 kg) were used in a 2 × 3 + 1 factorial arrangement of treatments with 6 pens per treatment. Factors were 3 crop residues (corn cobs, wheat straw, and corn stover) and 2 treatments where crop residues were either fed (20% diet DM) in their native form (NT) or alkaline treated with 5% CaO (DM basis) and hydrated to 50% DM before anaerobic storage (AT). Intakes were not affected by diet (F test; P = 0.30). An interaction between chemical treatment and residue (P < 0.01) was noted for final BW, ADG, G:F, and HCW. Greater final BW was observed for treated stover (4.6%) and straw (5.6%) compared with NT residues; however, AT and NT cobs were similar. Treated straw (9.7%) and stover (12.5%) resulted in greater ADG (P < 0.01) and improved G:F (10.7% and 5.0%, respectively; P < 0.01) compared with NT forms. In Exp. 2, ruminally fistulated steers (n = 5) were used in an unbalanced 5 × 7 incomplete Latin square design with a 2 × 3 + 1 factorial arrangement of treatments. Factors were crop residue (corn cobs, wheat straw, and corn stover) and chemical treatment (NT or AT) fed at 25% of diet DM. Greater DM (73.7% vs. 66.1%; P < 0.01), OM (77.0% vs. 68.5%; P < 0.01), fat (89.2 vs. 85.2; P = 0.02), and NDF (66.8% vs. 51.5%; P < 0.01) digestibilities were noted for AT than for NT. However, no difference (P > 0.10) was observed between control (46% corn; DM basis) and AT (31% corn; DM basis) for DM digestibility (70.7% vs. 73.7%) or OM digestibility (72.1% vs. 77.0%). Dry matter intakes were not different between treated and untreated diets (P = 0.38), but lower (P < 0.01) NDF intake was observed for treated diets (3.1 vs. 3.5 kg/d), suggesting that CaO treatment was effective in solubilizing some carbohydrate. These data suggest that 15% replacement of corn and 10% untreated residue with treated forage result in a nutrient supply of OM similar to that of the control. The improvements in total tract fiber digestibility that occurred when treated forages were fed may have been related to increased digestibility of recoverable NDF and not to increased ruminal pH. Feeding chemically treated crop residues and WDGS is an effective strategy for replacing a portion of corn grain and roughage in feedlot diets.