Mineral metabolism of sheep fed saltbush or a formulated high-salt diet

Old man saltbush (Atriplex nummularia) is sown in saline farming systems worldwide, and is commonly utilised as fodder for livestock. Saltbush contains very high concentrations of NaCl and KCl, however, the complex interactions between minerals means that sheep grazing saltbush may be susceptible to mineral deficiencies. The aim of this experiment was to assess the effect of high NaCl and KCl intakes on the apparent absorption of some macro-minerals (Mg, Ca, P) by sheep fed formulated high-salt diets or old man saltbush to help identify likely mineral deficiencies. Two experiments were conducted. In both experiments 18-month-old Merino wethers were offered one of 4 diets at maintenance: a control pellet (no added salt), control pellet + 10% salt (low salt), control pellet + 20% salt (high salt), or old man saltbush containing approximately 20% salt. The salt addled to all diets was 2NaCl:1KCl. Sheep were fed the diets for a minimum of 3 weeks before any measurements were taken. In the first experiment we measured the accumulation of Na and K in the rumen of cannulated sheep for 24 h following feeding. In the second experiment we measured the apparent digestion and absorption of Na, K, Cl. Mg, Ca and P over 6 clays. There was a net loss of Mg (0.83 g/day), Ca (0.61 g/day) and P (0.46 g/day) from sheep fed the saltbush diet, but the addition of salt to the control pellet and high levels of Na and K in the rumen had no effect on the apparent digestion and absorption of Mg, Ca and P. The loss of Mg, Ca and P from the gastrointestinal tract of sheep fed saltbush is likely to be clue to a combination of reduced availability and absorption of minerals from the saltbush leaves. Deficiencies in Mg. Ca and P can reduce animal production and even cause stock deaths. These results indicate that saltbush as a sole source of feed may be unsuitable for sheep with high nutritional demands, and further research is required to fully assess the mineral balance of sheep grazing saltbush pastures. (C) 2010 Elsevier B.V. All rights reserved.