Effects of high dietary lead on the metabolism of intravenously dosed selenium-75 in dairy calves.

The metabolism of intravenously dosed 75Se was studied in 10 Holstein bull calves fed for ad libitum access a control diet containing no added Pb or a control diet supplemented with 1000 ppm Pb as PbSO4 for 4 wk. The Pb-supplemented calves exhibited no clinical signs often ascribed to lead toxicity. Likewise, feed intake and body weight gains were not affected adversely. The lead content of rib, kidney, liver, and brain was increased. Serum glutamic oxaloacetate transaminase activity increased in the calves fed Pb during the last 2 wk of the experiment. The kidneys of the calves supplemented with lead were 34% larger than those of controls. The total endogenous 75Se in the feces over the 4-d collection period was not different between treatments (4.14% of dose versus 3.31% of dose). Likewise, urinary 75Se excretion values were similar. About 97% of the 75Se dose disappeared from the blood within 6 h after dosing four calves on both treatments. Tissue concentrations of 75Se were reduced in kidney, spleen, pancreas, brain, and spinal cord. In summary, ingested Pb had very little effect on the endogenous excretion of 75Se in urine and feces; therefore, the data are consistent with earlier research in which the main effect of Pb on Se occurs at the absorption site.