Abstract:
DIET SELECTED BY SHEEP GRAZING ON ANNUAL PASTURE IN SOUTHERN VICTORIA I. F. DAVIS * I. INTRODUCTION Growth of pasture in southern Victoria occurs during autumn, winter and particularly spring. The pasture matures and dries off in late spring and thereafter only dry, vegetative material, burr and seed are present. Sheep grazing on the pastures usually maintain weight for 6-8 weeks after the pasture dries off, but little is known about what they eat. Information on this is presented here. II. EXPERIMENTA L The observations were part of a larger study of animal, pasture inter-relationships on annual pasture at Werribee, 20 miles west of Melbourne. The annual rainfall is 20 in. (508 mm). The pasture consists predominantly of Wimmera rye grass (Lolium rigidum Gaud.) and subterranean clover (Trifolium subterraneum L .) . The area was divided into one acre plots, on each of which four, five or seven sheep grazed. Half of the plots received a top-dressing of 60 lb of nitrogen per year as urea. There were three replicates of each treatment. The present observations were confined to plots grazed by four and seven sheep. An oesophageal fistula was made in one animal on each plot by the method of Torell, as described by Tribe and Peel (1963). Material eaten was determined by examination of extruded material on each of two to four days in October and December, 1963, and February, 1964. The extruded material was collected in plastic-lined bags during a grazing period of 30 min duration shortly after dawn. Immediately following collection, a sample of 30-40 g was taken and stored in a screw-top glass jar at 3' DupliC. cate 10 g subsamples were sorted for botanical analysis within 48 hr. The proportions of grass and clover in the extruded material were calculated after drying at 100�C for 24 hr. III. RESULTS AND DISCUSSION (a) Animals The grazing behaviour of the sheep with oesophageal fistulae appeared unaffected by the fistulation. The change in bodyweight of these animals throughout the period of observation was closely similar to that of others on the plot and they tended to graze with the other animals. (b) Changes in the pasture In October, when observations were initiated, the pasture was in a green, vegetative stage. By December the pasture components had flowered, set seed and *Department of Agriculture Animal Husbandry Research Centre, Werribee, Victoria 249 dried off, leaving much standing grass 'hay', except on the plots which did not receive nitrogen and were grazed by seven sheep; here there was only sparse dry material. In February standing grass 'straw ' was still present in some quantity, but the 'no nitrogen' plots grazed by seven sheep looked bare, although on close examination they were found to contain dry, vegetative fragments; mostly of grass but with some clover and clover burr. (c) The material eaten Of the oven-dried matter in the extruded material, grass comprised 20-97% in October, 77-97% in December and 4-20% in February (Table 1). In October, the proportion of grass in the extruded material was quite variable, suggesting that the sheep had no strong preference for grass or for clover. However, in December, unless the proportions of grass and clover in the pasture had changed considerably, as seems unlikely, the animals must have selected for grass at that time. Since there was still much grass residue on the plots in February, the sheep must have selected the clover residues at this time. Most of the material eaten in February was vegetative material or burr. Clover seed, usually thought to sustain sheep on such pastures, constituted no more than 2% of the extruded material. TABLE 1 Proportion of grass in oesophageal extrusa IV. ACKNOWLEDGMENTS I wish to thank the staff of this laboratory and Dr R. H. Watson, in particular, for help and advice. The work was undertaken with funds provided by the Department of Agriculture, Victoria, and by a Commonwealth Sheep and Wool Research Grant. V. REFERENCES T RIBE , D. E., and P EEL ,L YNETTE A gricdtural Research 14: 330. (1963). Tota l salivation in lambs. Australian Journal of 250