Hens fed 5%, but not 3% FO had lower (P < 0.05) body weight at the end of study compared with the control group (Table 4). Supplementation of microalgae A at 7.5 or 10% caused hens fed 5% FO to maintain body weights similar to the control. Neither microalgae nor FO affected average daily feed intake, plasma uric acid concentration, egg production, or the weights of whole egg, albumen (egg white), egg yolk as well as egg shell. Compared with the control diet, diets supplemented with 7.5 or 10% microalgae A decreased (P < 0.05) plasma alkaline phosphatase activity. Both plasma inorganic phosphorus concentration and alkaline phosphatase activity in hens fed diets supplemented with microalgae A (regardless of presence of FO) were lower (P < 0.05) than those of hens fed 3 and(or) 5% FO alone.