Differences between sheep excreting sodium predominantly in their urine or in their faeces: the effect of changes in sodium intake

Sheep receiving a total of about 31 mmol day‐1 (0.5 mmol kg‐1) of sodium were classified according to the predominant route of sodium excretion; urinary (U) or faecal (F). U sheep had a greater water turnover than F sheep; their intake was 41% higher and they produced 133% more urine but there was little difference in faecal water loss. Most faecal sodium was readily exchangeable with water in both groups. When sodium intake was reduced by 80% (to 6 mmol day‐1; 0.1 mmol kg‐1), the reduction in total sodium excretion was equally effective in F sheep and U sheep after 48 h and after 2 weeks the overall losses of sodium were smaller in F sheep. On sodium intakes close to requirement (0.1 mmol kg‐1 or less) the majority of the sheep excreted most of their sodium in faeces and did so on intakes up to 0.5 mmol kg‐1 day‐1. Excess dietary sodium is mainly excreted renally. When sodium intake is increased abruptly (by 20 mmol day‐1, 0.3 mmol kg‐1), total sodium excretion only increases gradually but after about 3 days it ‘overshoots’ as in humans.