Submitted to: Agronomy Society of America, Crop Science Society of America, Soil Science Society of America Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/2007
Publication Date: 11/4/2007
Citation: Mackown, C.T., Phillips, W.A., Northup, B.K. 2007. Do elevated nitrate concentrations in wheat forage affect performance of fall stocker cattle [abstract]. Agronomy Society of America, Crop Science Society of America, Soil Science Society of America Meeting, November 4-8, 2007, New Orleans, LA. 2007 CD-ROM. Interpretive Summary: Abstract Only
Technical Abstract: Winter wheat (Triticum aestivum L.) is the predominate cool-season forage grown in the southern Great Plains and is considered excellent forage capable of producing gains greater than 1.4 kg/day in stocker cattle (Bos taurus L.). Occasionally properly processed stocker cattle gain little or no weight after initial turnout on fall wheat pasture. Shoots of small grain cereals can accumulate elevated concentrations of nitrate that reportedly pose performance and health risks to ruminants. From 2002 to 2006 we measured nitrate concentration of clipped wheat samples within 8 d of the onset of fall grazing and recorded weight gains of yearling stocker steers after 23 to 69 d of grazing. Yearly broadcast applications of 45 kg N/ha were made 2 to 4 weeks before forage sampling, except in 2004 when 90 kg N/ha was applied. Across years forage nitrate-N differed as much as 11-fold (range 590 mg/kg DW in 2002 to 6600 mg/kg DW in 2004). Cattle weight gains ranged from -0.03 to 1.34 kg/day. The -0.03 kg/day value occurred in 2004. A high stocking rate (1,900 kg/ha) was chosen in 2004 because of abundant fall forage (3960 kg/ha), but excessive rain (13 cm; about 3-fold > normal) leading up to and after initiation of grazing resulted in severe pasture trampling and only 23 d of grazing. With 2004 results excluded, the correlation between cattle weight gains and forage nitrate concentrations (590, 760, 1300, and 1600 mg/kg DW) was not significant (P = 0.89). Even though the two highest nitrate levels were above the lowest value considered safe for all cattle, livestock weight gains were unaffected.