Chronic renal disease is a common cause of nonregenerative anemia in animals. Erythropoietin is normally produced by the peritubular endothelial cells in the renal cortex. Animals with renal disease produce less erythropoietin, leading to anemia. Recombinant human erythropoietin (44–132 U/kg, three times/wk, with most animals starting at 88 U/kg) has been used for treatment. PCV is monitored weekly until the desired improvement is reached (this will vary with the initial degree of anemia), after which the dosage is decreased. Animals receiving recombinant human erythropoietin require supplemental iron to support RBC production. (Also see Hematinics.) Darbepoeitin also has been found to be valuable in management of anemia associated with chronic kidney disease.