PS13-24. Mitigating Summer Forage Deficits: A Pilot Evaluation of Prussic Acid–Free Sorghum × Sudangrass in Beef Grazing Systems.

Abstract Seasonal declines in cool-season perennial pasture productivity (“summer slump”) reduce forage mass, nutritive value, and animal performance in Kentucky beef systems. Adoption of warm-season annual forages has been limited, however, due to producer concerns regarding nitrate accumulation and prussic acid toxicity. The objective of this study was to evaluate forage yield, nutritive value, and animal performance of a novel prussic acid–free sorghum × sudangrass (PAF) cultivar relative to conventional warm-season annual forages. In a completely randomized design, Angus cows (n = 12) were randomly assigned (n = 4 per treatment) to one of three forage treatments: brown mid-rib sorghum × sudangrass (BMR), pearl millet (PML), or PAF. Treatments were established in 929 m² plots and replicated in triplicate; however, the third grazing cycle was terminated early due to elevated nitrate concentrations. Cattle grazed assigned treatments until sward height reached approximately 50 cm. Forage yield was quantified throughout the grazing period, and samples were collected and analyzed for dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), total digestible nutrients (TDN), and nitrate concentration. Animal performance was evaluated using average daily gain (ADG), and respiration rate (breaths/min) was recorded as an indicator of physiological response. Data were analyzed using SAS v. 9.4. Dry matter yield was greater (P < 0.01) for PAF (4,448 kg/ha) compared with BMR (3,553 kg/ha) and PML (2,979 kg/ha). Nitrate concentration was greater (P = 0.02) in BMR (1,520 ppm) than in PAF and PML (1105 and 1070 ppm, respectively). Average daily gain did not differ among treatments (0.6 kg/d; P ≥ 0.05). Respiration rates were similar among treatments, averaging 29.75, 29.06, and 32.63 bpm (AM) and 34.13, 30.31, and 31.50 bpm (PM) for BMR, PML, and PAF, respectively (P ≥ 0.05). These results indicate that PAF provides greater forage yield while maintaining comparable animal performance and physiological responses relative to conventional warm-season annual forages. The PAF system represents a viable, reduced-risk alternative to traditional sorghum-based forages and may improve producer confidence and adoption of warm-season grazing strategies to mitigate seasonal forage limitations.