Magnification and Shrub Stemmy Material Influences on Fecal Analysis Accuracy

Abstract

When 100X and 200X microscope magnification levels were used singly and interchangeably in microhistological analysis, magnification level had no effect (P<.05) on diet botanical composition of 60% grass and 60% forb diets containing 6 forage species fed to mule deer. However, large differences occurred between magnification levels for individual plant species in a 60% shrub diet containing the same forage species. The use of the 100X and 200X magnification levels interchangeably was slightly more accurate than exclusive use of either magnification level for the high grass and high shrub diets. For fecal analysis our study shows 100X and 200X microscope magnification levels can be used singly or interchangeably with little influence on accuracy. Use of the 100X magnification level to scan fields for potentially identifiable fragments followed by switching to 200X magnification for better resolution of fragments difficult to discern can slightly improve both speed and accuracy. Fourwing saltbush, which had a high proportion of stemmy material relative to leaves, was severely underestimated in the feces of all 3 diets. Our data indicate fecal analysis has limited value as an estimator of diets of herbivores, such as mule deer, that consume significant but variable quantities of stemmy material from shrubs.