Three double-marker systems were used in cannulated steers offered straw-based diets supplemented with barley, fishmeal or a combination of both, in an attempt to reduce the risks of misinterpreting biological results based on calculations of digesta flows using markers. Ruthenium phenanthroline (Ru-phe), ytterbium acetate (Yb-ac) and the indigestible acid detergent fibre fraction (IADF) were used as markers of the particulate phase of digesta in conjunction with Cr-EDTA as a liquid-phase marker to estimate duodenal and ileal digesta flows. The present paper presents the difficulties met in the application of marker techniques. The particulate marker used in a double-marker system for calculation of nutrient flow modified the degree of statistical significance observed for dietary treatment effects on digesta flow parameters. The data suggest that the type of diet used affects the behaviour of individual markers in different ways and could incur some bias in the results. It is hypothesized that the physical and chemical characteristics of digesta, in different dietary conditions, can be responsible for differential attachment of markers to particles of the solid phase. In such cases, the distinction made in the double-marker technique between particulate and liquid phases may not be sufficient to correct for lack of representativeness of digesta contents sampled from T-shaped cannulae. For the diets studied it was concluded that the interpretation of digestion parameters should be based on both Ru-phe and Yb-ac results. © 1990, Cambridge University Press. All rights reserved.
