269. Herbage and Animal Productivity of Two Rotational Cow-Calf Grazing Strategies in the Southern Great Plains.

Abstract Adaptive grazing, which typically involves short grazing periods at high stocking density and variable rest intervals based on vegetation recovery, has been suggested to improve grazing efficiency and long-term pasture sustainability; however, its effects on herbage and animal productivity remain poorly understood. This 4-yr study (2022-2025) evaluated the effects of adaptive grazing (AD, high stocking density and flexible rest periods) and prescriptive grazing (PR, low stocking density and fixed 75-d calendar rotations) on herbage and animal productivity in native rangelands in Southern Oklahoma. The experiment followed a randomized complete block design with three replicated blocks. Within each block, pair pastures (10-12 ha each) were randomly assigned to either AD or PR. Each treatment was stocked with a herd of 50 Angus crossed cow-calf pairs (total of 25,521 kg). Although animals’ numbers varied among years, total stocking weight was maintained similar between treatments. Herbage production was calculated as the difference between pre and post grazing herbage mass and summed within each year. Animal productivity was expressed as stock days, calculated as total animal unit (1 AU = 454 kg liveweight) multiplied by grazing days and divided by pasture area (ha). Grazing treatment, year, and their interaction were analyzed as fixed effects, and block as random, with least square means estimated using the emmeans package in R and Tukey-adjusted comparisons. Annual precipitation was 12% below 30-y historical average in 2022-2024, and 23% above average in 2025. Across the years, AD and PR averaged 8.3 and 13 grazing events, respectively. Rest periods were longer under AD (125 days) than PR (77 days), and stocking density under AD was 14, 14, 12, and 21 times greater than PR in 2022, 2023, 2024, and 2025, respectively. Herbage production did not differ between grazing treatments (P = 0.77), but increased over time, with greater production in 2025 compared to 2022 (P = 0.003). Animal productivity was greater under AD compared to PR (151 vs. 111 AUD/ha/year, P = 0.07), and increased across years, with greater values in 2024 and 2025 compared to 2022 (P = 0.03). A significant grazing treatment × year interaction was observed for cumulative stock days, with AD resulting in 1.4 times greater values than PR by the end of 2025 (598 vs. 440 AUD/ha, respectively, P = 0.02). Favorable environmental conditions in 2025 resulted in greater herbage production and grazing capacity than in previous years. Although herbage production and annual stock days did not differ between grazing treatments within individual years, the greater cumulative stock days under AD across the 4-y period suggests improved forage use efficiency under adaptive grazing.