ID # 22-24 LEAF BLADE SELECTION BY SHEEP IN KLEINGRASS (Panicum coloratum L.) PASTURES WITH DIFFERENT DEFERMENT PERIODS

The winter use of standing dead biomass produced by warm season grasses during the previous growing season may be an alternative to grazing systems in the semi-arid Pampean Region of Argentina. This study evaluated: 1) the effect of different deferment periods on the leaf blade percentage and quality of ‘kleingrass’ (Panicum coloratum L.), a warm season specie recently introduced to that region, and 2) whether rams grazing the vegetation accumulated during these different periods are able to select leaf blades to maintain the quality of their diets. It was generated three treatments by deferment of the forage produced after harvesting in mid December 1987 (T1), and in early January (T2) and early February (T3), 1998. Length of the deferment reduced (P<0.05) the percentages of leaf blade from 42.2+0.01 % to 30.5+2.40%. However, the percentage of blades in ram diets remained stable (62+5.4%; P>0.05). The percentage of crude protein (CP) in the vegetation was not affected by the length of the deferment period (P>0.05), however CP contents in the blades were twice higher than in the rest of the vegetation (4.13+0.9 vs 1.82+0.34). Rams actively selected leaf blades in all the treatments (P>0.05), but selection effort was stronger in those with longer deferment. These results indicated that rams are able to made an effort to select the plant part of highest quality, and suggest that this effort is restricted by the vegetation structure.