Influence of end-grazing forage residual and grazing management on lamb growth performance and crop yield from irrigated dual-purpose winter wheat
D. R. Miller A C D , G. J. Dean A and P. D. Ball BA Tasmanian Institute of Agricultural Research, University of Tasmania, PO Box 46, Kings Meadows, Tas. 7250, Australia.
B Tasmanian Institute of Agricultural Research, University of Tasmania, 13 St Johns Avenue, New Town, Tas. 7008, Australia.
C Present address: 49 Merino Street, Toowoomba, Qld 4350, Australia.
D Corresponding author. Email: Moramby13@bigpond.com
Animal Production Science 50(6) 508-512 https://doi.org/10.1071/AN09163
Submitted: 30 November 2009 Accepted: 2 March 2010 Published: 11 June 2010
Abstract
The effects of end-grazing forage residual and continuous v. rotational grazing systems on prime lamb performance, grain yield and quality were examined in an irrigated dual-purpose winter wheat (cv. Mackellar) crop in Tasmania. The design was a two end-grazing residual (400 and 800 kg/ha of dry matter (DM) at Zadoks Growth Stage 30, Low and High respectively, 0.2 ha plots) × two grazing system (continuously, or rotationally grazed in four subplots) factorial, replicated three times. Mixed-sex, second-cross lambs [37 kg liveweight (LW), 2.5 body condition score, 45 kg DM/head initial feed allowance] grazed for a total of 46 days before removal. Initial feed availability was 1875 kg DM/ha, with final residuals of 520 ± 57 and 940 ± 70 kg DM/ha for the Low and High treatments respectively. Particularly for the Low residual, in vitro DM digestibility and crude protein at stem elongation were reduced (P < 0.05) by rotational compared with continuous grazing. The weekly lamb growth rate (g/day) during the first 5 weeks of grazing was linearly related to average weekly available DM in kg/ha (GR = 0.35 ± 0.041 × DM – 194 ± 49.0, P < 0.01, R2 = 0.56). Total LW produced (336 ± 11.7 kg/ha), and grain yield (6.9 ± 0.21 t/ha), protein (11.4%), screenings <2.2 mm (10.9%) and 100 grain weights (3.82 g DM) were not different between treatments. There were no advantages of rotational grazing compared with continuous grazing. Irrigated dual-purpose winter wheat can be continuously grazed by lambs up to a 500 kg DM/ha residual at stem elongation without compromising total LW produced, grain yields or grain quality.
Acknowledgements
This study was supported financially by Meat and Livestock Australia. The authors acknowledge the generous provision of the trial site and animals, and assistance in animal handling, by Stewart and Gordon McGee. Technical assistance was provided by A. Robertson, R. Parkinson, J. Sykes, B. Davey, G. Crisp, P. Dolan, S. Gatenby, A. Fowles, and R. Smith. Surgical preparation and care of fistulated wethers was performed by B. Jackson and C. Gulbrandson. R. Thompson and the late P. Williams also contributed to trial planning and implementation. Ross Corkrey provided statistical advice.
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