Modelling the effect on stocking rate and lamb production of allowing ewes to graze a dual-purpose wheat crop in southern New South Wales
S. R. McGrath A B C E , J. M. Virgona B D and M. A. Friend A B CA School of Animal and Veterinary Sciences, Charles Sturt University, PO Box 588, Wagga Wagga, NSW 2678, Australia.
B Graham Centre for Agricultural Innovation, Locked Bag 588, Wagga Wagga, NSW 2678, Australia.
C Future Farm Industries CRC, University of Western Australia, Crawley, WA 6009, Australia.
D Present address: Graminus Consulting Pty Ltd, 1 Heron Place, Wagga Wagga, NSW 2650, Australia.
E Corresponding author. Email: shmcgrath@csu.edu.au
Animal Production Science 54(10) 1625-1630 https://doi.org/10.1071/AN14251
Submitted: 12 March 2014 Accepted: 16 June 2014 Published: 19 August 2014
Abstract
Slow pasture growth rates during winter limit the potential gross margins from autumn and early winter lambing in southern New South Wales (NSW) by limiting stocking rates and/or increasing supplementary feed requirements. Dual-purpose crops can reduce the winter feed gap in mixed-farming systems by increasing the available feed in winter. The simulation software AusFarm was used to model a mixed-farming system at Wagga Wagga with Merino ewes joined to terminal sires and grazing lucerne-subterranean clover pasture over a 41-year period. A paddock of dual-purpose wheat was then added to the system, and ewes were allowed to graze the wheat crop when feed on offer reached 850 kg DM/ha and before GS31. Weaned lambs were sold after late August if lamb growth rates fell below 20 g/head.day, mean lamb weight reached 45 kg or production feeding of lambs was required. Lambing in June resulted in the highest median gross margin whether or not ewes were able to graze the wheat crop during winter. Grazing of a dual-purpose wheat crop resulted in greater proportional increases in gross margins as stocking rate was increased, increased lamb production and reduced supplementary feeding costs, and reduced interannual variability in gross margin returns.
Additional keywords: AusFarm, feed gap, lambing time, lucerne.
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