are listed in Many of the characteristics of the cows used in this study Table 3. shows no The variation among cows in sand particle excretion times indication of correlation with: a. cow age, b. cow weight, c. cow weight losses during the study, d. days of lactation, e. fecal output rates, f. milk production rates, ge urine output rates, h. water consumption rates (as indicated by urine, milk, and feces production), or : i. gross food consumption rates (as indicated by fecal output). Results from this experiment indicate that the excretion patterns and retention times for various sizes of debris particles which cattle ingest are roughly predictable from previously reported observations for fine and coarse food materials. Although considerable variation was observed in retention times among the study animals on similar diet regimes, similar variation would be expected from results of conventional studies using marked food materials. Since transuranic elements should be absorbed subsequent to the reticulorumen (Barth and Mullen, 1974), where larger particles are retained longer than small particles, the longer retention of large particles may offset somewhat the higher solubility rates for the smaller. The net result should be to cause the biological availability or absorption of transuranic elements from large and small particles to be less different than solubility rates (e.g., as a function of particle size) would indicate. Because cattle are not normally maintained in very close proximity to nuclear events, most particles which could be ingested should be very small. By either air or water transport mechanisms, the large heavy particles tend not to be transported over large distances. Therefore, the rapid passage of the 20-um particles observed in this experiment is particularly pertinent to generally assess transuranic-particle passage through cattle. 164