[Investigations on the development of hyponatremia in older calves with diarrhea].

The study involved 50 hospitalized calves (four weeks to five months old) suffering from diarrhoea and hyponatraemia (blood sodium concentration below 130 mmol/l). Starting from the day of admission blood, urine, and faecal samples were taken each morning and sodium and potassium concentrations were measured. In addition, blood and urine samples were taken in the evenings, if electrolytes had been given orally during the day. The obtained values from urine samples were compared with the plasma concentrations in order to check for inadequate renal excretion of electrolytes. Consistency of the faeces and visible blood admixture were the main criteria in the evaluation of electrolyte concentration in the 317 samples of faecal water. With one exception no inadequate renal losses of sodium were observed. Sodium and potassium concentrations in faecal water showed a distinct negative correlation. As the consistency of faeces grew increasingly normal, electrolyte contents of faeces approached those reported for adult cattle, i.e. potassium levels rose and sodium levels decreased. Visible blood admixtures had no significant effect on the sodium and potassium concentrations in the faeces. A distinct relationship between electrolyte contents in faecal water and the consistency of the faeces was found. There were highly significant differences in electrolyte concentrations between faeces of watery (Na: 82 +/- 21 mmol/l; K: 23 +/- 12 mmol/l) and soupy (Na: 54 +/- 26 mmol/l; K: 42 +/- 19 mmol/l) consistency (mean +/- standard deviation). By contrast, soupy and pulpy faeces just showed a slight or no difference in electrolyte concentrations. Only faeces of watery consistency contained approximately as much sodium as observed in neonatal calf diarrhoea. These results show that the pronounced hyponatraemia in older calves can hardly be attributed to loss of sodium via faeces and urine. The following possible causes are proposed: (a) older calves usually have access to water (therefore there is more gradual dehydration or no dehydration at all); (b) oral electrolyte solutions are seldom administered.