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 density on grazing efficiency and forage selectivity in tall fescue (Festuca arundinacea Schreb.)-subclover (Trifolium subterranum L.) hill pastures 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 the low density/longer duration (10-day) than for higher density/shorter duration (2-day) treatments. Greater grazing efficiency as duration increased largely reflected higher rates of intake rather than lower levels of non-consumptive forage destruction. Stocking density within a constant grazing duration (2 days) had little effect on grazing efficiency. Within the 10 day grazing treatment, grazing efficiency was highest 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 duration/very high density compared to longer duration/lower density treatments in this study. These results suggest that the very short duration with very high stocking density was not an attractive management option since grazing efficiency was low and sheep were more selective.