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Evaluation of Polyethylene, Chromic Oxide, and Cerium-144 as Digestibility Indicators in Burros¹

Agricultural Research Laboratory of the University of Tennessee, Oak Ridge, Tennessee³

An experiment was designed to study the relative effectiveness of three external indicators in the determination of nutrient digestibility in burros. Eight mature male burros received Cr₂O₃ and polyethylene in their diet, and no restrictions were placed on their physical activity. Rectal "grab" fecal samples were collected for a 10-day period, pooled and analyzed for organic matter, crude fiber, crude protein, ether extract and nitrogen-free extract as well as the 2 indicators. Differences in digestion coefficients based on these indicators were not statistically significant. Subsequently, six fo the burros were confined in metabolism stalls and received daily doses of ¹⁴⁴Ce in addition to the Cr₂O₃ and polyethylene. After a 10-day total collection period, samples were analyzed for the nutrients mentioned earlier and the 3 indicators. Differences between digestion coefficients based on polyethylene, ¹⁴⁴Ce, and the total collection of feces were not statistically significant; those based on Cr₂O₃ were significantly (P < 0.05) lower. The low digestion coefficients based on Cr₂O₃ were directly attributed to the low recovery of this indicator. Recovery of Cr₂O₃ was 81.5% as compared with 96.6% and 103.2% of the ¹⁴⁴Ce and polyethylene, respectively. Crude protein digestion was significantly decreased (P < 0.025), and ether extract digestion was significantly increased (P < 0.025), when the burros were in metabolism stalls.

² Department of Animal Husbandry-Veterinary Science, University of Tennessee, Knoxville.

³ Operated by the Tennessee Agricultural Experiment Station for the U.S. Atomic Energy Comission under Contract no. AT-40-1-GEN-242.

Manuscript received 7 January 1967.