Two experiments involving dosing sheep with 60Co were conducted to determine the effect of plant species on cobalt retention. Two digestibility trials with different levels of dietary cobalt were conducted to attempt to detect the effect of cobalt level upon nutrient digestibility. Experiment 1 was a 2 × 2 factorial design with sheep adjusted to a ration of alfalfa or timothy hay and then given a small portion of the same forage species grown in cultures with 60Co in the nutrient medium or administered 60CoCl2 via capsule. The retention of radioactive colbalt in the sheep and excretion in feces and urine was followed with a low level radiation counter. Seventy-one to 83% of the dose of 60Co was excreted within 48 hours. There was no difference in excretion pattern between animals receiving cobalt in a capsule and those receiving it in forage. Virtually all of the dose was excreted within 5 days. The feces contained 98 to 100% of the excreted activity. No activity was detected in the urine of timothy-fed sheep. Whole body counts of alfalfa-fed sheep were lower (P<.05) than timothy-fed sheep at 2, 3, 4 and 5 days after administration of the isotope. This reflects the faster excretion rate of the major portion of cobalt in the alfalfa-fed sheep during this period. After 11 days the counts in the alfalfa-fed sheep were higher (P<.05) indicating greater retention of 60Co. In experiment 2, sheep received alfalfa or timothy hay with 0 or added cobalt and were drenched with a 60Co solution. The 60Co activity disappeared at two rates. The rapid rate is assumed to represent gastrointestinal tract passage and the slow rate body loss of the absorbed isotope. The rate of loss of the slow component of the alfalfa-fed sheep was less than in timothy-fed sheep.
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Looney et al. (1976) studied this question.