Crude Protein and Nitrate Concentrations of Fall Forage for Stocker Cattle: Wheat vs. Perennial Cool-Season Grasses.

Pastures of winter wheat (Triticum aestivum L.) are the primary source of cool-season forage used by stocker cattle (Bos taurus L.) in the southern Great Plains. Replacing some wheat pasture with perennial cool-season grass (PCSG) pastures could reduce uncertainties of sufficient fall forage and reduce annual tillage operations that are costly and lead to soil loss. Wheat is considered excellent forage capable of producing stocker weight gains > 1.4 kg/day, but wheat can accumulate high levels of nitrate that can pose a health risk to the animals. We compared the levels of crude protein (CP) and nitrate in fall forage clipped four years (2002-2005) from replicated pastures of winter wheat and two PCSG pastures established in 2001 (‘Jose' tall wheat grass wheatgrass (Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang), ‘Manska' intermediate wheat grass (Thinopyrum intermedium (Host) Barkworth & D.R. Dewey), and one PCSG pasture established in 2002 (‘Lincoln' smooth brome grass (Bromus inermis Leyss)). Levels of CP in PCSG forage were > 148 g/kg DW, but depending on year were often as much as 21 to 37% less than that of wheat forage (244 ± 3 g/kg DW). Mean nitrate-N levels of wheat forage were 400, 1400, 4600, and 940 mg/g DW in 2002 through 2005, respectively. Among the PCSG forages, nitrate-N did not exceed 660 mg/g DW. The CP levels of PCSG were often substantially less than that of wheat, but were sufficient for growth of stocker calves. The nitrate risks that sometimes occur with wheat would make PCSG a safer choice for pasture.