[Obtaining fecal fluid from calves: dialysis compared to filtration]

To obtain faecal fluid from the calf by dialysis the following procedure was used: small dialysis bags filled with dextran 10% were placed in the cooled (4 degrees C) faecal sample to which gentamycin was added to inhibit fermentation. Equilibrium between dialysate and surrounding fluid was reached after 24 hours. However, depending on the consistency of the faeces, after 6 hours 90 to 95% of the final osmolality at 24 hours was reached. In regard to osmolality, sodium, potassium and chloride concentrations as well as to concentrations of short chain fatty acids no significant differences could be observed between the faecal fluid obtained by dialysis or by centrifugation (3500 g, 20 min, 4 degrees C) and subsequent filtration. Distinctly higher concentrations of calcium and inorganic phosphate were measured in the filtrates; a possible explanation is that these ions in faeces are largely present as poorly diffusible compounds (in particular with faeces of a more solid consistency) or are bound to the cell membranes.