44. Livestock Response to Alternative Annual Forages Under Semi-arid Conditions

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Abstract Producers operating in semi-arid and water-limited environments face increasing challenges due to fluctuating and unpredictable weather patterns. Irregular rainfall and rising temperatures have made forage production less reliable, underscoring the need for resilient forage species capable of maintaining productivity under climatic stress. In addition to weather uncertainties, producers face the issue of an ever-changing global economy, with increasing input costs and volatile livestock prices. Sorghum-sudangrass hybrids (Sorghum bicolor × S. bicolor var. sudanense) and pearl millet (Pennisetum glaucum) have gained attention as promising options due to their high biomass potential and tolerance to drought and low soil fertility. However, widespread adoption remains limited because these species can accumulate antinutritional compounds, particularly nitrates and dhurrin, which may pose risks to animal health when improperly managed. To evaluate the effects of continuous grazing of prussic acid free sorghum-sudangrass (PAF) and pearl millet (PM) on livestock health and performance, in 2023, 24 Angus-cross stockers (223 ± 32 kg) and, in 2024, 30 Angus-cross heifers (247 ± 19 kg) were continuously grazed in irrigated paddocks of each forage in New Deal, Texas. Body weight measures, collection of blood, urine, fecal samples, and forage grab samples were performed on a biweekly basis. Data was analyzed using PROC MIXED of SAS 9.4 to fit a random intercept model. Over both years, increased average daily gains were observed with PAF than PM, 0.94 vs. 0.59 kg/day, respectively (P < 0.005). Both forages had negligible levels of prussic acid (dhurrin-derived cyanogenic compound), below the toxicity threshold of 600 ppm. Meanwhile, both had measurable nitrate levels, with PAF at 400 ppm and PM at 1400 ppm (P < 0.005), which were well below the toxicity threshold of 10,000 ppm. No signs of adverse health effects were observed in cattle during or after the grazing period, indicating that both forages, when grazed appropriately, are safe and nutritionally adequate for livestock. These findings indicate that PAF is a more suitable forage option than PM for cattle production in water-limited environments.

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