Abstract:
The grazing value of two Australian cultivars of winter wheat was evaluated in two preliminary trials. In the first, March-sown crops of Blackbutt oats, Tennant and Gordon winter wheats and a mixture of Tennant and the extreme spring wheat Sunset (2:1) were grazed in July by young crossbred sheep (39.5 kg). Crop growth rates differed initially, so that herbage on offer at the start of grazing was significantly higher (P<0.05) for the oats. Crops were therefore grazed at equal initial herbage allowances of 40 kg DM/animal, to assess their capacity to support liveweight gain (LWG). Lambs grazing the winter wheats grew significantly faster (320-369 g/day; P<0.05) than those grazing the oats (282 g/day) or the Tennant:Sunset mix (252 g/day). Winter wheat grain yields were also significantly higher (4.45-4.30 t/ha: P<0.05) than either the oats (3.29 t/ha) or the mixture (3.72 t/ha), which did not differ. Compared with adjacent ungrazed areas, grain yields were not affected by razing. In the second trial, Tennant winter wheat was grazed for 56 days by second-cross lambs (34.2 kg), at an initial herbage allowance of 57 kg DM/animal. Weight gains were less than in the first trial, averaging 274 g/day in the first half of the grazing period and 199 g/day in the second half. This occurred despite the forage having very high digestibility (>80%) and crude protein content (>21%) throughout. The mean herbage intake estimated in 10 lambs was 1071 g DM/day. At slaughter, mean fat depth at the GR site was 14.4 mm, indicating that lambs were still lean. The results of the two trials indicate that winter wheat forage can support rapid LWG and finish lambs to market specifications. However, they also indicate the need for closer examination of the factors influencing weight gain during such grazing, in relation to the nutritive value of the crop and herbage intake.
