Crop and Pasture Science Crop and Pasture Science Society
Plant sciences, sustainable farming systems and food quality
RESEARCH ARTICLE

Variation within and between two saltbush species in plant composition and subsequent selection by sheep

Hayley C. Norman A C , Colby Freind B , David G. Masters A , Allan J. Rintoul A , Robyn A. Dynes A and Ian H. Williams B

A CSIRO Livestock Industries, Centre for Environment and Life Sciences, Private Bag 5, Wembley, WA 6913, Australia; and Cooperative Research Centre for Plant-based Management of Dryland Salinity, University of Western Australia, Crawley, WA 6009, Australia.

B School of Animal Biology, Faculty of Natural and Agricultural Sciences, University of Western Australia, Crawley, WA 6009, Australia.

C Corresponding author. Email: Hayley.Norman@csiro.au

Australian Journal of Agricultural Research 55(9) 999-1007 http://dx.doi.org/10.1071/AR04031
Submitted: 10 February 2004  Accepted: 4 August 2004   Published: 24 September 2004

Abstract

This work examines nutritive value and preference by sheep of 2 saltbush species, river saltbush (Atriplex amnicola) and old man saltbush (Atriplex nummularia). Both species are woody perennials that are native to Australia and used in commercial grazing systems. The hypothesis for this study was that sheep will graze saltbushes with higher nutritive value and lower secondary compounds in preference to bushes with lower nutritive value and higher secondary compounds. This was expected to be found both within and between the old man and river saltbush species.

To test the hypothesis, 10-month-old Merino ewes grazed a 10-ha plot containing a mixture of old man and river saltbush in approximately equal proportions. Within the plot, and prior to grazing, 20 bushes of each species were pegged for identification and samples of edible plant material collected for analysis. Each week during the grazing period the bushes were photographed for assessment of preference. Sheep preferred river saltbush to old man saltbush and also showed some preferences for specific bushes within each species. Differences in digestibility of dry matter and organic matter, crude protein, ash, oxalates, and nitrates were not clearly associated with differences in preference. Although the reasons for preferences were not demonstrated, the analysis of the plant material did indicate that the content of total ash and oxalates was at levels likely to depress voluntary feed intake.

Additional keywords: shrub biomass, salinity, preference, feed intake, protein, ADF, sulfur, oxalate.


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