METABOLISM OF RADIOMANGANESE AND RADIOZINC IN SHEEP — EFFECTS OF INTRARUMINAL DOSING WITH NITRILOTRIACETIC ACID

Abstract

Two experiments were carried out with rams fed a concentrate diet containing 17 and 27 ppm (air dry basic) of manganese and zinc, respectively. In the first, fistulated rams were dosed intraruminally with 54Mn and samples of rumen contents were taken at different times after dosing. A peak uptake of radiomanganese by mixed rumen bacteria was obtained within 2 h after dosing. The uptake by rumen protozoa was almost unchanged during the first 7 h after dosing. In the second experiment, eight fistulated rams were divided into two groups. One group was dosed intraruminally with 180 mg of nitrilotriacetic acid (NTA) twice daily (before each feeding) for 1 mo and then both groups were dosed intraruminally with 54Mn and 65Zn and total 96-h fecal and urinary collection was commenced. Samples of rumen contents were taken at 2 h. Ninety-six hours after the administration of the radioisotopes the sheep were killed and tissue samples removed. Significantly lower uptakes of 54Mn and 65Zn by the rumen bacteria and protozoa were obtained in the NTA-treated sheep than in control sheep. The uptake of 54Mn by the rumen tissue was significantly higher in the NTA-treated sheep. There were no differences between treatments in the urinary excretion of radioisotopes, while fecal excretion of 54Mn and 65Zn tended to be lower in the NTA-treated sheep. It was apparent that the absorption of 54Mn and 65Zn was slightly increased by intraruminal dosing of sheep with NTA but the rate of uptake of radiomanganese by soft tissues tended to be lower in the NTA-treated sheep.