Crude protein and nitrate concentrations of fall forage for stocker cattle: wheat vs perennial cool-season grasses

Authors: Mackown, Charles; Northup, Brian

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2010
Publication Date: 7/1/2010
Citation: Mackown, C.T., Northup, B.K. 2010. Crude protein and nitrate concentrations of fall forage for stocker cattle: Wheat vs perennial cool-season grasses. Crop Science. 50:2140-2147.

Interpretive Summary: Stocker cattle enterprises in the southern Great Plains rely upon winter wheat for forage between mid November to early March in graze + grain production systems and until late April in graze-out production systems. Replacing some wheat pasture with perennial cool-season grasses (PCSG) could reduce uncertainties of sufficient fall forage and annual tillage operations that are costly and lead to soil loss. Even though wheat is considered excellent forage capable it is known to accumulate toxic levels of nitrate and elevated protein levels associated with pasture bloat in ruminants. We compared levels of crude protein (CP) and nitrate in fall forage clipped four years (2002-2005), from replicated pastures of winter wheat and three PCSG pastures of tall wheatgrass, intermediate wheatgrass and smooth bromegrass. The CP levels of PCSG were often substantially less (21 to 37%) than that of wheat, but were sufficient for growth of stocker calves. Nitrate levels of wheat forage ranged from safe to toxic levels, while among the PCSG forages, nitrate levels were always in at a safe level. The nitrate risks that sometimes occur with wheat would make PCSG a safer choice for pasture. This research provides useful information to other researchers, consultants, and producers seeking alternatives to winter wheat pastures for stocker cattle.

Technical Abstract: 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 grasses (PCSG) could reduce uncertainties of sufficient fall forage and 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/d, but wheat can accumulate high levels of nitrate that pose a health risk to stockers. We compared 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 wheatgrass (Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang), ‘Manska' intermediate wheatgrass (Thinopyrum intermedium (Host) Barkworth & D.R. Dewey), and one PCSG pasture established in 2002 (‘Lincoln' SBG (Bromus inermis Leyss)). Levels of CP in PCSG forage were > 148 g/kg DW, but were 21 to 37% less, depending on year, than that of wheat forage (244 ± 3 g/kg DW). Mean nitrate-N levels of wheat forage were 400, 1400, 4600, and 840 mg/kg DW in 2002 through 2005, respectively. Among the PCSG forages, nitrate-N did not exceed 660 mg/kg 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.