SHEEP GRAZING EFFICIENCY AND SELECTIVITY ON OREGON HILL PASTURE

Grazing trials were conducted during early and late spring of 1988 and 1989 to evaluate the impact of sheep grazing duration and stocking de nsity on grazing efficiency and forage selectivity in tall fescue (Fes tuca arundinacea Schreb.)-subclover (Trifolium subterranum L.) hill pa stures near Corvallis, Ore. Grazing treatments were 2, 6, and 10 days duration with corresponding stocking densities 380, 130, 78, and 1,390 , 460, and 280 ewes/ha during early and late spring trials each year, respectively. Grazing efficiency was generally greater (P<0.05) for th e low density/longer duration (10-day) than for higher density/shorter duration (2-day) treatments. Greater grazing efficiency as duration i ncreased largely reflected higher rates of intake rather than lower le vels of non-consumptive forage destruction. Stocking density within a constant grazing duration (2 days) had little effect on grazing effici ency. Within the 10 day grazing treatment, grazing efficiency was high est during the last 4 days and lowest during the first 2 days (P<0.05) . Although short duration/high density grazing is considered to be non -selective, sheep were equally or more selective under very short dura tion/very high density compared to longer duration/lower density treat ments in this study. These results suggest that the very short duratio n with very high stocking density was not an attractive management opt ion since grazing efficiency was low and sheep were more selective.