The effect of the quantity and quality of pasture available to sheep on their grazing behaviour

During the spring of 1969 four originally similar plots of a Phalaris tuberosa subterranean clover pasture were grazed at different stocking levels to produce a range in levels of pasture availability. The plots were subsequently grazed at 12, 16, 20, and 24 sheep per acre in a 4 x 4 Latin square design. On these pastures, as the amount of pasture available decreased, there was a significant increase both in the nitrogen content of available material and in the diet selected by oesophageal-fistulated sheep grazing them. These differences in the quantity and quality of available pasture produced significant changes in the grazing behaviour of sheep. Grazing time showed a linear increase with decreasing pasture availability, but the rate of increase in grazing time was insufficient to maintain liveweight. Ruminating time was significantly reduced as pasture availability declined. There were considerable differences between sheep in their ability to increase their grazing times as pasture availability decreased. These differences could be of considerable practical implication.