CSIRO PUBLISHING www.publish.csiro.au/journals/ajar Australian Journal of Agricultural Research, 2005, 56, 427–434 Feed intake and production in sheep fed diets high in sodium and potassium David G. Masters A,C , Allan J. Rintoul A , Robyn A. Dynes A , Kelly L. Pearce A,B , and Hayley C. Norman A A CSIRO Livestock Industries, Centre for Environment and Life Sciences and Cooperative Research Centre for Plant-based Management of Dryland Salinity, Private Bag 5, Wembley, WA 6913, Australia. B Division of Veterinary and Biomedical Science, Murdoch University, Murdoch, WA 6150, Australia. C Corresponding author. Email: David.Masters@csiro.au Abstract. Salinity is a problem facing many crop and livestock producers in southern Australia. One management option is to revegetate with salt-tolerant plants suitable for animal production. These plants are often halophytic shrubs containing up to 30% ash, predominantly as sodium, potassium, or chloride. This experiment examines the consequences of a high intake of sodium and potassium separately or together on feed intake, digestibility, liveweight change, and wool growth. Twelve groups of 6 weaner wethers were allocated to treatments according to a balanced 3 × 4 factorial design with 3 levels of added potassium (0, 0.38, and 0.77 mol/kg DM equivalent to 0, 15, and 30 g/kg DM) and 4 levels of added sodium (0, 0.87, 2.18, and 3.48 mol/kg DM, equivalent to 0, 20, 50, and 80 g/kg DM) as the chloride salts. The treatment diets were fed to sheep for 6 weeks. Increasing sodium in the diet significantly decreased feed intake, digestibility, liveweight gain, and wool growth either as a main effect or through an interaction with potassium. Organic matter intake was reduced from 1.35 kg at the lowest levels of sodium and potassium to 0.67 kg at the highest levels. Comparing the same 2 groups, liveweight gain was reduced from 144 to 0g/day, organic matter digestibility from 59.1% to 57.3%, and wool growth from 1.21 to 1.04 mg/cm 2 .day. The response surfaces indicate that production was depressed even at the lower levels of sodium, whereas high potassium depressed intake, digestibility, and liveweight gain at high levels of sodium only. The interaction between sodium and potassium was always negative at high levels of sodium, indicating that manipulation of the proportions of the 2 elements is unlikely to provide benefits for animal production when total salt levels are high. Although wool growth was depressed at high sodium and potassium, the efficiency of wool growth increased from 10.0 to 15.4g/kg organic matter intake when the lowest and highest levels of the sodium and potassium were compared. This result may present significant opportunities for the use of saline land to grow fine wool. Additional keywords: salt, salinity, wool growth, digestibility. Introduction Current estimates are that 5.7 Mha are at risk from dryland salinity in Australia; much of this is in areas used for grazing ruminants (National Land and Water Resources Audit 2001). In southern Australia, land too saline for conventional crops may be revegetated with halophytic shrubs (particularly Atriplex and Maireana spp). These shrubs are usually grazed in autumn in Mediterranean climates when annual pastures are dry and senesced. Although the halophytic shrubs produce biomass when grown on moderate to highly saline soils, livestock performance is often less than expected (Warren and Casson 1994; Morcombe et al. 1996). The high levels of soluble salts in the plants (up to 30%) (Norman et al. 2002) usually mean that there is a low digestible organic matter content in the dry matter (DOMD) so that, even if the organic matter digestibility (OMD) is reasonable, animals still need to consume high levels of dry matter (DM) to meet the energy requirements for maintenance or growth. High concentrations of sodium chloride in feed or water have been shown to depress food intake (Peirce 1957; Wilson 1966b), alter the size and frequency of meals (Rossi et al. 1998), and lower the efficiency of conversion of digestible energy (DE) to metabolisable energy (ME) (Arieli et al. 1989). It is therefore possible that even with unlimited quantities of edible plant material on halophytic shrubs, the high salt levels would cause a suppression in appetite and this would result in weight loss. The aim of this experiment is to provide information for use in the development of strategies to improve the use of halophytic shrubs. Specifically, the aims are to quantify © CSIRO 2005 10.1071/AR04280 0004-9409/05/050427