• Chromic oxide contamination of pasture previously used in marker studies

      Sprinkle, J. E.; Kress, D. D.; Doornbos, D. E.; Anderson, D. C.; Tess, M. W.; Ansotegui, R. P.; Olson, B. E.; Roth, N. J. (Society for Range Management, 1995-05-01)
      Fecal output of range cows was determined during 2 periods of summer (period I) and late summer (period II) grazing using a constant release intraruminal Cr2O3 bolus. Chromic oxide contamination was determined by analyzing forage for Cr2O3 and by obtaining fecal samples from cows prior to bolusing. Control cows were also monitored along with the experimental cows during grazing periods. The overall herd least squares mean for fecal output during period I was lower than the expected value by 48%. Forage during period I contained an average of 55.7 microgram Cr2O3 g-1 of forage or about 45% of the daily dose of the bolus. Forage during period II contained an average of 38.3 microgram Cr2O3 g-1 of forage or about 29% of the daily dose of the bolus. Our results indicate that comparisons of fecal output least squares means by period of the year can be biased by Cr2O3 contamination of forage in pastures which have been previously used for marker studies.
    • Technical Note: Physical factors that influence fecal analysis estimates of herbivore diets

      Bartolomé, J.; Franch, J.; Gutman, M.; Seligman, N. G. (Society for Range Management, 1995-05-01)
      Microhistological analysis of epidermal fragments in feces is often used to estimate the diet of herbivores but is not generally accepted as a consistently reliable method. Gross errors arise, especially when diets are composed of herbage components with widely different morphological and structural characteristics. The present study investigated the possibility of using such physical characteristics to improve the reliability of the method. Over a 7 day period, 4 rumen-fistulated beef cows were given a fixed diet composed of a shrub, a grass, and a forb component. On the last 2 days, samples of rumen content and feces were taken for analysis of epidermal fragment. Forbs were under-estimated, grasses over-estimated, and shrubs correctly estimated. Correction factors to estimate true diet composition were defined as the biomass represented by the specific epidermal fragments (epidermal weight index) and the degree of degradation to which the epidermis is subjected in the digestion process (epidermal erodibility factor). These factors account for characteristic physical features of the different dietary components and were measured directly or were derived from the calibration experiment. The utility of such factors depends on accurate determination of the component variables and may be overshadowed by sampling error and observer bias in the microhistological identification of epidermal fragments.