Effects of pasture availability and liveweight on the feeding of grass hay to grazing sheep

Abstract

In the first of two experiments the amount of hay (69% organic matter digestibility) eaten by 1.5 -year-old Corriedale wethers when fed every 2 d was measured in a series of grazing trials to study the effects of pasture availability and liveweight. The greatest amount of hay (1 .8 kg/head. 2 d) was eaten on dry summer pasture, but consumption fell when green growth appeared. During winter, on slow growing pastures, hay consumption (1.3 kg/head .2 d) was highest at about 0.7 t herbage (DM)/ha, but less hay was consumed on plots with lower amounts of pasture. On pasture more abundant than 0.7 t DM/ha hay intake decreased, but small amounts were still eaten at very high yields (about 5 . 0 t DM/ha). Pooled data of all winter observations yielded the following expression for predicting the organic matter intake of hay voluntarily eaten when fed every 2 d (y, g/2 d) from the quantity of pasture available (x, t DM/ha): Y = 330 + 738exp (- 0.0322x4) : r2 = 0.87 ; P < 0.01 Various weather conditions experienced in different periods of one trial changed the responses slightly. Wet or frosty weather reduced hay consumption on sparse pasture relative to that on fine days. Heavy animals (49-57 kg) ate more hay (450 vs 170 g/d) at high availabilities than light animals (44 kg) and spent less time grazing than light animals (5 vs 7 h) indicating a preference by lighter animals for a high quality diet from pasture. In the second experiment, daily consumption of hay (61 % organic matter digestibility) and pasture were estimated at a range of pasture availabilities (0.5- 1.5 t DM/ha). When hay was fed, each 100 kg increment in pasture dry matter availability decreased the voluntary organic matter intake of hay by 57 g/d, while apparent consumption of pasture organic matter increased by 92 g/d. Grazing time was not reduced as much as expected from the substitution of hay for pasture, from 10 h with no hay to 9 h when fed, and suggests a slow rate of pasture intake with selection of higher quality material to complement the hay diet. A practical implication of these results is that heavy animals in good condition will eat hay in preference to grazing pasture, while lighter animals which are assumed to have a greater need for supplement prefer to consume the higher quality pasture.