397 Effect of corn harvest with a chopping head on performance of cattle grazing corn residue

Abstract The addition of stalk chopping equipment on combine heads has become more common. An advantage of grazing residue compared with baling, is the ability of cattle to select the more digestible plant parts (husk and leaf). Chopping may impact this ability and decrease the feeding value. Thus, this study was designed to evaluate the effects of chopping residue at harvest on grazing cattle performance. A cornfield (16 Mg grain/ha) was divided into 12 paddocks blocked by location within field and assigned randomly to be harvested using a chopping or non-chopping combine head, with 4 paddocks assigned to be grazed (1.05 ha) from each harvest method (HM) and 4 ungrazed. Growing steers [n = 40; body weight (BW) = 230 ± 3.5 kg] were stratified by BW and assigned randomly to a grazed paddock, with 6 steers in the west block and 4 steers in the east block, with 1 rumen canulated steer (484 ± 33 kg BW) being assigned to each of the east paddocks and used as diet samplers. This resulted in the same grazing pressure (2.9 animal units/ha) in grazed paddocks. Cattle were supplemented at 0.6 % of initial BW with a distillers dried grains plus solubles and mineral mix daily. Cattle grazed for 56 d resulting in 5.4 Animal Units Months/ha. Residue mass of three 0.58 m2 frames was sampled in each paddock before (d -1), during (d 36) and after grazing. Husks were collected from three 5.81 m2 areas per paddock at each of the three timepoints. For residue mass, there was a significant (P < 0.01) HM by time interaction. There was no difference (P = 0.34) in residue mass between HM prior to grazing. However, at 36 d into grazing, residue mass of standard was greater (P = 0.03) than chopped, and post-grazing residue mass of chopped was greater (P = 0.01) than standard. When husk (kg/ha) was evaluated, there was a significant (P < 0.01) HM by time by grazing interaction. Prior to grazing, there was no difference (P ≥ 0.66) in husk between the grazed and ungrazed paddocks within HM. However, husk was less (P < 0.01) for chopped than standard. On d 36, within HM, grazed had less (P < 0.01) husk than the ungrazed. However, within grazing status on d 36 there was no effect (P ≥ 0.52) of HM. Post-grazing there were no differences (P ≥ 0.19) in husk among treatments. Within grazed treatments there was greater (P < 0.01) husk prior to grazing initiation compared with both D36 and post-grazing which did not differ (P ≤ 0.85). Within ungrazed treatments, pre-grazing and D36 did not differ (P ≥ 0.10) in husk, however, husk was lesser (P > 0.01) at the post-grazing sampling. For ADG there was no difference (P = 0.20) between HM, with 0.37 and 0.31kg/d for standard and chopped, respectively. Overall, HM had no effect on grazing cattle performance.