Effect of corn residue harvest method with ruminally undegradable protein supplementation on performance of growing calves and fiber digestibility

Two experiments evaluated the effects of corn residue harvest method on animal performance and diet digestibility. Experiment 1 was designed as a 2 × 2 + 1 factorial arrangement of treatments using 60 individually fed crossbred steers (280 kg [SD 32] initial BW; = 12). Factors were the corn residue harvest method (high-stem and conventional) and supplemental RUP at 2 concentrations (0 and 3.3% diet DM). A third harvest method (low-stem) was also evaluated, but only in diets containing supplemental RUP at 3.3% diet DM because of limitations in the amount of available low-stem residue. Therefore, the 3 harvest methods were compared only in diets containing supplemental RUP. In Exp. 2, 9 crossbred wethers were blocked by BW (42.4 kg [SD 7] initial BW) and randomly assigned to diets containing corn residue harvested 1 of 3 ways (low-stem, high-stem, and conventional). In Exp. 1, steers fed the low-stem residue diet had greater ADG compared with the steers fed conventionally harvested corn residue ( = 0.03; 0.78 vs. 0.63 kg), whereas steers fed high-stem residue were intermediate ( > 0.17; 0.69 kg), not differing from either conventional or low-stem residues. Results from in vitro OM digestibility suggest that low-stem residue had the greatest ( < 0.01) amount of digestible OM compared with the other 2 residue harvest methods, which did not differ ( = 0.32; 55.0, 47.8, and 47.1% for low-stem, high-stem, and conventional residues, respectively). There were no differences in RUP content (40% of CP) and RUP digestibility (60%) among the 3 residues ( ≥ 0.35). No interactions were observed between harvest method and the addition of RUP ( ≥ 0.12). The addition of RUP tended to result in improved ADG (0.66 ± 0.07 vs. 0.58 ± 0.07 for supplemental RUP and no RUP, respectively; = 0.08) and G:F (0.116 ± 0.006 vs. 0.095 ± 0.020 for supplemental RUP and no RUP, respectively; = 0.02) compared with similar diets without the additional RUP. In Exp. 2, low-stem residue had greater DM and OM digestibility and DE ( < 0.01) than high-stem and conventional residues, which did not differ ( ≥ 0.63). Low-stem residue also had the greatest NDF digestibility (NDFD; < 0.01), whereas high-stem residue had greater NDFD than conventional residue ( < 0.01). Digestible energy was greatest for low-stem residue ( < 0.05) and did not differ between high-stem and conventional residues ( = 0.50). Reducing the proportion of stem in the bale through changes in the harvest method increased the nutrit