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Two experiments were conducted to determine the effect of estrogenic growth implants on P excretion of sheep and cattle in concentrated animal feeding operations (CAFO). In experiment 1, fifty-four Rambouillet wether lambs were either implanted with 12 mg zeranol or not implanted and housed in pens of 3 to 4. Lambs were fed a finishing diet for 56 d. At 14-d intervals, the pen floor was cleaned thoroughly and P content determined. From d 0 to 42, 53.7% of consumed P was excreted, and from d 42 to 56, 79.8% of consumed P was excreted onto the pen surface. In experiment 2, because a large number of growing cattle are implanted with estrogenic growth implants before entering the feedyard, we conducted this study to determine P excretion from cattle previously implanted when grazing pasture. Eighty crossbred steers were implanted with no implant, 20 mg estradiol + 200 mg progesterone or 8 mg estradiol + 40 mg trenbolone acetate and grazed for 179 d. Steers were then transported to the feedyard and housed in 9 pens based upon previous implant treatment (3 pens per implant treatment). Steers were given ad libitum access to a high-concentrate diet for 137 d. At the end of the feeding period, pen surface manure was collected, weighed and sampled for P analysis. During the feeding period, cattle consumed 21.5 g of P per head daily and 11.0 g/d of the consumed P accumulated 1 Reference to a company or trade name does not imply endorsement by the Texas Agricultural on the pen surface. Implant strategy before entering the CAFO did not affect (P > 0.10) the efficiency of P utilization in the CAFO.