A comparison of the forage value for sheep of buckwheat and sorghum stubbles grown on the Southern Tablelands of New South Wales

Two grazing experiments were conducted to evaluate buckwheat and sorghum stubbles as forage for sheep. The stubbles were stocked by young crossbred wethers at 10 and 20 ha-1 for 55 days on the buckwheat and 81 days on the sorghum. Measurements were made at regular intervals of the availability and composition of plant material, diet selection, the intake of digestible organic matter (DOM) and liveweight change, while wool production was measured over each experimental period. More than one-third of the sheep grazing buckwheat stubble were affected by fagopyrism (buckwheat poisoning) and this probably reduced both liveweight gain and wool production. Buckwheat residues had a similar nitrogen content to sorghum (1 .0% vs 0.87%), but a lower organic matter digestibility (43.7% vs 57.1%). Mature buckwheat plants were not eaten readily. Mean liveweights of sheep on buckwheat stubble declined throughout the experimental period and overall changes were -3.8 and -7.0 kg for the low and high stocking rates, respectively. Corresponding values for sheep on sorghum stubble were 0.3 and -4.6 kg, although weight losses at the higher stocking rate did not occur until after 40 days grazing. For the same length of grazing as the buckwheat (55 days) the liveweight changes for sorghum were 0.2 and -1.2 kg, respectively. Wool growth rate was low for both stubbles but was more than 60% higher for sheep on the sorghum. Values for each stocking rate were 3.86 and 2.67 (g clean dry wool day-1) for the buckwheat, and 5.39 and 4.33 for the sorghum. It was concluded that sorghum stubble is a useful source of grazing for sheep on the Southern Tablelands but buckwheat stubble, because of its low acceptability, poor nutritional value and the risk of fagopyrism, is of very limited value.