127. Two-Year Assessment of Supplementation Feeding Strategies on Stocker Calf Performance Grazing Mixed Grass Prairie in Western Oklahoma

Abstract Growing steers grazing rangelands during the summer often require supplementation to offset nutrient deficiencies and achieve adequate body weight gain. Rising costs of fuel and labor can prohibit frequent supplement delivery to livestock in extensive grazing systems. To evaluate supplementation delivery methods under these constraints, a two-year stocker calf supplementation trial was conducted at the Marvin Klemme Range Research Station near Bessie, OK. In Year 1, 150 crossbred steer calves (BW = 282 ± 11 kg) were used over 140 days; in Year 2, 149 calves (BW = 286 ± 10 kg) were used over 145 days. Calves were randomly assigned to one of two treatments: 1) hand-fed dried distillers grains (DDGS) cubes (HF), offered three times per week at 2.63 kg/steer each feeding (1.13 kg·animal⁻¹·day⁻¹), or 2) self-fed extruded DDGS pressed blocks (PB) provided in 91-kg tubs. All pastures (n = 8 per year) were stocked at 2.43 ha/animal. Trials were divided into two grazing periods: Early Season (ES) and Late Season (LS). Data were analyzed using linear mixed-effects models in R (R Core Team, 2024) with treatment and year as fixed effects and pasture nested within year as a random effect. Supplement intake differed between treatments during ES (P = 0.007), where HF calves consumed more supplement (1.13 vs. 1.04 kg·d⁻¹ for Cube and PB, respectively). No differences were observed in LS intake (P = 0.706). Across the full trial, HF calves consumed more supplement overall than PB calves (1.13 vs. 1.05 kg·d⁻¹; P = 0.023). Despite these intake differences, body weight at initiation, midpoint, and final harvest did not differ (P ≥ 0.468). Average daily gain (ADG) did not differ between treatments during ES or LS (P ≥ 0.178), nor across the total grazing season (0.87 vs. 0.84 kg·d⁻¹ for HF and PB, respectively; P = 0.204). A cost sensitivity analysis, considering mileage costs of $1.25 to $1.56 per km and estimated feed costs of $0.58/kg for DDGS cubes and $1.22/kg for PB, indicated that a round-trip feeding route of 87 km would be required for reduced delivery costs to offset the higher cost of pressed blocks. Thus, performance outcomes were comparable between treatments, suggesting that pressed block tubs may provide a practical alternative when labor and fuel costs are limiting factors. In conclusion, supplementation using pressed block tubs can be as effective as hand-feeding DDGS cubes three times per week for stocker calves grazing mixed grass prairie in western Oklahoma. Ensuring consistent intake from free-choice blocks, particularly early in the grazing season, remains key to optimizing performance.