Comparison of genetically engineered microbial and plant phytase for youngbroilers

This study was conducted to compare the efficacy of genetically engineered microbial (Natuphos(R)) and plant (Phytaseed(R)) phytase for enhancing the utilization of phytate P in corn-soybean meal-based diets fed to young broi lers and to evaluate the safety of Phytaseed(R) phytase. Three levels of ea ch of the two sources of phytase (250, 500, and 2,500 U/kg of diet) were ad ded to a corn-soybean meal basal diet containing 0.46% total P, 0.21% nonph ytate P, and 0.92% Ca. There were eight cages per treatment (eight birds pe r cage for Weeks 2 to 3 and seven birds for Weeks 4 to 5), except for the b asal diet without added phytase that had 16 cages. Cage BW and feed consump tion were recorded weekly. During Week 5, cage excreta samples were collect ed for determination of apparent retention coefficients of DM, Ca, and P. A t the end of Week 5, all birds were killed, and the left and right toes wer e removed for determination of toe ash weight and percentage. Forty birds ( one per cage from the diet without added phytase and diets with 500 or 2,50 0 U phytase/kg from both sources) were randomly selected for gross necropsy and histologic evaluation of liver, kidney, and bone tissues. Addition of both sources of phytase resulted in similar increases (P < 0.05) of BW gain ; feed intake; gain:feed; apparent retention of DM, P and Ca; and toe measu rements. Phosphorus excretion decreased as phytase addition increased. No s ignificant abnormalities were seen in any of the 40 broilers necropsied. Fu rther, the fit of a nonlinear function revealed that most measurements reac hed a plateau at 2,500 U/kg. Based on performance, bone characteristics, an d retention of P, Ca, and DM of young broilers, the efficacy of Phytaseed(R ) phytase was similar to that of Natuphos(R) phytase for enhancing the util ization of phytate P in corn-soybean meal-based diets. General necropsy and histologic examination of liver, kidney, and tibial tissues revealed no ad verse effects of phytase source or level.