Repeated Grazing Affects Quality and Sampling Strategies of 'WW B. Dahl' Old World Bluestem

Abstract

Selective grazing can exaggerate the difference between quality of standing forage in the pasture as a whole, and quality of forage actually consumed.  In research paddocks near Lubbock, TX, repeated grazing by steers caused spatial heterogeneity in the nutritive value of Bothriochloa bladhii (‘WW B. Dahl’ old world bluestem) that was not accounted for by standard sampling techniques.  Forage in repeatedly grazed and avoided areas was sampled on Sept. 1, 2010.  Entire plants sampled at the standard clipping height in avoided areas had greater acid detergent fiber (ADF), neutral detergent fiber (NDF), cellulose, and lignin, and lower net energy for maintenance (NE_m) and crude protein (CP) than tops of plants had in both areas.  Crude protein differed between tops of plants in avoided (5.3%) and repeatedly grazed (7.4%) areas.  Thus, B. bladhii sampling strategies should account for animal-imposed variation in pastures when herbage allowances exceed those required by grazing animals.