Comparison of the alkane-based herbage intakes and the liveweight gains of young sheep grazing forage oats, dual-purpose wheat or phalaris-based pasture

Two experiments were conducted between 2004 and 2006 near Canberra, Australia, to provide information about herbage intake and liveweight gains of young sheep grazing dual-purpose crop cf. pasture. In an indoor feeding trial (2004-2005), dual-purpose wheat (cv. Mackellar) and oats (cv. Blackbutt) had estimated organic matter (OM) digestibilities of 0.849 +/- 0.0070 and 0.847 +/- 0.0001, respectively. The indoor trial also provided data for the concentrations and faecal recoveries of the cuticular wax alkane and long-chain alcohol (LCOH) markers used to estimate diet composition and intake in the grazing trial. The faecal recoveries of both alkanes and LCOH were well described by asymptotic regressions. Alkane recovery differed between crops, though not between years. Faecal LCOH recovery did not differ between crops or years. Under grazing conditions in 2004-2005, the OM digestibility (OMD) of crop herbage was 0.825-0.871, significantly higher than the OMD of phalaris-based pasture (0.752-0.758). The estimated OMD of wheat in 2006 (0.792) was lower than in the earlier years. Sheep consumed similar to 1 kg/day digestible OM intake (DOMI) from crop in 2004-2005. In 2004 this was significantly higher than the DOMI of sheep grazing pasture (0.75 kg/day) whereas in 2005 the DOMI from pasture was slightly (1.15 kg/day) but significantly higher than that from crop (mean 0.97 kg/day). Regardless of the source of herbage consumed, sheep daily liveweight gains were in the range 200-250 g/kg DOMI. Liveweight gains of sheep grazing crop were also predicted from their calculated metabolisable energy intakes and requirements for maintenance and were within 1% of the observed liveweight gains. Our results demonstrate that in high-rainfall areas, the quantity and quality of the herbage provided by sowing dual-purpose crops, and the resultant increased animal liveweight gains, justify the inclusion of dual-purpose crops in grazing systems.