Annual Forages: Influence on Animal Performance and Water/Nutrient Management

Annuals can provide short-term grazing between crop rotations or can be interseeded into perennial pastures to increase forage quality and productivity. They provide an opportunity to increase the economic and environmental sustainability of traditional grazing systems. However, to be profitable, annuals must produce a significant amount of highly nutritious forage within a short time (3 – 6 months). In a 2-yr plot study, 70 d after planting, rapeseed (Brassica napus L.) and turnip (B. rapa L.) produced 1,484 and 1,023 kg DM/ha, respectively. The CP, NDF, and ADF were similar for both forages (average of 26.2, 17.9, and 13.8%, respectively). Daily production of CH₄ and CH₄ per gram of NDF fed were 84 and 80% lower, respectively, in turnip and rapeseed compared with annual ryegrass (ARG; Lolium multiforum Lam.) when fed in continuous culture. Wheat (Triticum aestivum L.)/ARG, triticale (× Triticosecale)/ARG, and wheat/triticale/ARG pastures provided similar grazing days per hectare, ADG, and cost of gain (375 d/ha, 1.44 kg/d, and $1.46/kg BW, respectively) in a grazing study in the Gulf Coast region. No-till (NT) establishment was shown to be as effective as conventional tillage for establishing small grain pastures in the Ozark Plateaus. Furthermore, stocker performance during the fall was not affected by tillage treatment, but during the spring grazeout, BW gain per hectare was 8% greater in NT pastures. Research in Southern Piedmont has shown that brown mid-rib sorghum-sudangrass (BMR SSG; Sorghum bicolor var. bicolor × bicolor var. sudanense) and pearl millet [PM; Pennisteum glaucum (L.) R.Br.] with crabgrass [Digitaria sanguinalis (L.) Scop.] tended to have greater ADG (0.98 kg/d) than sorghum-sudangrass or PM alone (0.85 kg/d). Feeding of BMR SSG reduced daily production of CH₄ and CH₄ per gram of NDF fed by 66 and 50%, respectively, compared with a perennial cool-season forage in continuous culture. Additional research in the Southern Piedmont has shown that interseeding of cool- and warm-season annuals into a perennial pasture reduced the concentration of NO₃-N and PO₄-P in runoff by 50 and 36%, respectively. Annuals not only provide economic incentives to producers, but also potentially reduce nutrient runoff, increase soil cover, increase soil carbon sequestration, and decrease enteric CH₄ emissions. However, establishment method, grazing management, and weather conditions all play important roles in the productivity and environmental impact of these systems. Further research is needed to better characterize how management and climatic conditions impact the long-term economic and environmental sustainability of grazing annuals.