[Comparison between dialysis methods and centrifugation/filtration for collecting fecal fluid from calves]

Faecal samples of different consistency from 15 calves were subjected to two methods to separate faecal fluid. Osmolality as well as the concentrations of electrolytes and short chain fatty acids were determined for each of the fluid samples obtained and the results compared. For 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; the probable explanation is that these ions in faeces are largely present as poorly diffusible compounds (in particular with faeces of a more solid consistency) or bound to the cell membranes.