Table 7. Retention Times for Sand Particles in Dairy Cows (Days) Particle Size (um) 200 Retention Time 20 80 Mean Retention Time* 0.8 3.2 3.9 5.2 Average Time for 50% 1.7 3.5 4.2 5.1 1.4-1.8 2.5-6.0 2.7-7.0 3.0-7.5 Average Retention 1.8 5.0 6.0 7.3 Average Time for 90% 2.8 7.6 8.7 10.0 2.2-3.2 5.5-9.7 5.5-11.2 Excretion** Range Time*** Excretion** Range 450 6.4-11.5 *Calculated as 1.44 times the average half-time given in Table 5. **Time required after dosing to excrete X% of the particles, average and range for experimental data. **kkTime required after dosing to excrete 67% of the particles, from experimental data. 162