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Background -- In southern Australia up to 2 million hectares of land in the high rainfall and mixed farming zones is affected by dryland salinity. Despite our best efforts to counter this problem through the strategic management of recharge areas, over the next 20 years more land will become saline, leaving some individual farmers with up to 30% of their property affected. Much of this land may never be returned to its former condition. However, it has been suggested that approximately 50% of salt affected land is suitable for improvement by planting halophyte-based (salt tolerant) pastures. This has significant implications for animal production, as only the grazing industry has the existing infrastructure and markets to make productive use of such land on this scale. Accordingly, a key aim of the CRC is to understand the consequences, opportunities and risks associated with feeding ruminants high salt diets, as well as other secondary compounds known to accumulate in halophytic plants. Objectives -- To determine the physiological and functional implications of feeding high salt diets to grazing ruminants, so that risks and benefits can be identified, and production systems optimized, to make the best use of saline land. Design -- A program of research has been designed to investigate numerous aspects of salt tolerance in ruminants, from the level of the farm production system, through studies on the individual animal, down to the molecular level of cellular responses. Comparative studies using cattle, and various breeds of sheep selected for meat or wool production, will help to identify the existing species and breeds that are best suited to grazing salty pastures. Physiological responses of sheep to high salt diets are being measured, in terms of diet selection, feed intake, digestibility, growth rate, feed conversion efficiency, and water requirement. The effect of a salt load on fetal development has been investigated in pregnant sheep and their lambs. Endocrine markers of the response to NaCl are being sought, with a view to developing rapid screening, selection and toxicity tests. The way in which salt affects rumen microorganisms is being investigated at the molecular level, and physiological responses are being measured in both plants and sheep after grazing saltbush, to identify and characterize the effects of secondary compounds in a halophyte diet. Outcomes -- Dietary NaCl decreases feed intake and digestibility in ruminants in a concentration-dependant manner, and beyond a concentration of approximately 12% NaCl, growth in sheep is depressed significantly. Nevertheless, sheep will select a high energy/high protein feed that is also high in salt, in preference to a feed that is low in salt, protein and energy, and will combine high and low salt feeds to improve the overall quality of their diet. At low levels of NaCl (up to 8% dry matter) cattle appear to tolerate salty diets better than expected, and do not show the same depression in feed intake observed in sheep. Furthermore, at high salt concentrations (20% dry matter), feed efficiency is improved markedly in cattle (and to a lesser extent in sheep), such that body weight is maintained for up to 6 wk, despite a 50% reduction in organic matter intake. When a salt load of 15% NaCl was administered to ewes throughout pregnancy, no detrimental effects were observed on blood pressure, lambing rate, or lactation, with some evidence that the pattern of water consuption and urine output in their lambs is altered following an acute salt challenge. Both insulin and leptin concentrations are altered by feeding salty diets, but further work is needed to isolate the direct effects of NaCl from those mediated by associated changes in feed intake. Only a small proportion of the rumen microbial population is able to tolerate high concentrations of NaCl added to rumen fluid in vitro.… [ABSTRACT FROM AUTHOR]