Steer Performance Grazing Corn Residue and Supplemented with Modified Distillers Grains Plus Solubles with or without Urea

A 72-d growing study was conducted to evaluate the effects of supplementing growing calves grazing corn residue with modified distillers grains plus solubles (MDGS; 1.4 or 2.3 kg/d) with or without urea on growth performance. Crossbred steers (initial BW = 244; SD = 19 kg) were utilized in a randomized block designed experiment with a 2×2 factorial arrangement of treatments. Factors included level of MDGS inclusion (1.4 or 2.3 kg) in the diet and inclusion of urea in the supplement (0 or 0.05 kg/d). Steers were individually supplemented daily via a Calan gate system. Beginning on November 2, steers were grazed on irrigated and non-irrigated corn residue depending on BW block (heavy block = irrigated field, light block = non-irrigated field). There were no significant MDGS × urea inclusion interactions observed. Urea inclusion level (0 and 0.05 kg/d) did not affect supplement DMI (P = 0.59), ADG (P = 0.41) or ending BW (P = 0.96). Steers fed 2.3 kg of MDGS had an increased (P < 0.01) ADG and a heavier (P < 0.01) ending BW compared to steers fed 1.4 kg MDGS daily. Corn plant components were collected prior to grazing (4 replications collected per field with 10 plants per replicate) to determine the in vitro organic matter digestibility (IVOMD), digestible organic matter (DOM) and CP of the residue. The husk component had the greatest IVOMD (P < 0.01), DOM (P < 0.01) and CP (P < 0.01) content; the leaf blade component was intermediate, and the leaf sheath component was the least (P < 0.01). There were no differences (P = 0.73) in IVOMD or DOM among corn residue components sampled off the irrigated and non-irrigated fields. Diet samples were collected at the beginning, middle and end of the trial to determine the nutritive value of the corn residue over the grazing period. There was a significant (P < 0.01) field × time interaction for CP content of diet samples. Over time, CP of the diet samples decreased numerically (P = 0.16), samples collected from steers grazing irrigated corn residue in November was greater (P < 0.05) in CP compared to the other samples collected. Digestibility of steer diet samples did not change (P ≥ 0.84) between irrigated and non-irrigated corn residue over all three collection time points. In conclusion, supplemental urea is not necessary when supplementing at least 1.4 kg MDGS to steers grazing corn residue.