Effects of increasing supplementation rates of extruded distillers’ grains cubes on stocker steer production grazing native range in Western Oklahoma

Our objectives were to determine the response curve of increasing supplementation rate with extruded distillers' grains (DDG) cubes for animal performance, supplement conversion ratio, and N excretion by steers grazing midgrass prairie in western Oklahoma. A 2-yr trial was conducted at the Marvin Klemme Range Research Station (Klemme) and the USDA-ARS Southern Plains Experimental Range (SPER) in western Oklahoma. At Klemme, steers (Yr 1, <i>n</i> = 133, BW = 247 ± 24.5 kg; Yr 2, <i>n</i> = 134, BW = 264 ± 29.1 kg) were allocated to 6 pastures in Yr 1 and 7 pastures in Yr 2 which were assigned to three daily supplementation rates of DDG cubes: (i) Negative Control (NC)- no supplementation; (ii) Low supplement (LS) - 0.91 kg/steer and (iii) Medium Supplementation (MS) - 1.82 kg/steer. At Klemme, steers were stocked at 2.0 ha/steer in yr 1 and 2.8 ha/steer in yr 2. At SPER steers (<i>n </i>= 119 each year; Yr 1, BW = 295 ± 28.8 kg; Yr 2, BW = 294 ± 25.7 kg) were allocated to 12 pastures stocked at 2.0 ha/steer with pastures assigned to: (i) NC; (ii) LS; (iii) MS and (iv) High Supplement-daily supplementation rate of 2.72 kg/steer. Data were analyzed by year and experimental site as a completely randomized design. Least-squares means were separated using orthogonal polynomial contrasts. In both years at Klemme, the increased supplementation rate linearly increased (<i>P </i>≤ 0.01) average daily gain (ADG) but made no difference (<i>P</i> ≥ 0.16) in supplement conversion ratio. At SPER, ADG increased linearly (<i>P </i>< 0.01) in Yr 1, but quadratically (<i>P </i>= 0.05) in Yr 2; in both years, supplement conversion ratio displayed a quadratic response (<i>P </i>= 0.01), decreasing with increasing supplementation rate. These data suggest that supplementing extruded DDG cube to steers grazing native range is a viable option to intensify production on stocker operations. If forage availability and nutritive quality is adequate to support BW gains higher supplementation rates are likely not economically efficient, however if forage is limiting improved performance may be adequate for positive economic returns. The response curves observed in this research will allow producers to make supplementation decisions based on market and range conditions.