Selecting Appropriate Markers for Digestibility Studies


Bernard JB, Ullrey DE, Wolff PL. 1995. Selecting appropriate markers for digestibility studies. In Proceedings of the First Conference on Zoo and Wildlife Nutrition, AZA Nutrition Advisory Group, Scarborough, OT.


Markers provide a method for indirect quantitation of digestive parameters. Gastrointestinal physiology and kinetics show a tremendous variation among species that is undoubtedly a reflection of evolution and dietary adaptation. Therefore, markers used in nutrition research must be appropriately selected for each species and each circumstance. Markers serve to facilitate quantification of passage rate and digesta fill as well as the relationship between intake and diet digestibility. They are generally administered by one of two techniques, either as a constant level in the diet or as a Pulse (or bolus) dose. By definition, markers are closely associated with the fractions of the digesta, are non-absorbable by the animal, and do not interfere with the normal function of the gastrointestinal tract. Additionally, it is a general assumption that the marker is in equilibrium with the pool of the fraction that it labels and that it is recoverable. Digesta may be divided into two fractions, a liquid phase and a particulate phase. Appropriate markers for most circumstances are those which are specific to a particular phase of the digesta. However, multiple marker systems in which both liquid and particulate fractions may be monitored simultaneously have been developed and successfully utilized in a number of species. Unfortunately, a perfect marker or marker system for all species does not seem to exist. Sensitivity to particular markers may cause a gastrointestinal upset that alters transit time, and in turn digestibility, eliminating the possibility of collecting valid data.

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