retention of phosphorus and nitrogen in growing pigs

It is well documented that the supplementation of pig diets with microbial phytase significantly improves the availability of phytate-bound phos-phorus, thus reducing its excretion to the envi-ronment (Jongbloed et al., 1992; Düngelhoef et al., 1994; Kornegay and Qian, 1996; Omogbenigun et al., 2003). Due to its chelating capacity, phytate may also form complexes with other nutritionally important minerals such as calcium, zinc or copper (Oberleas, 1973) as well as with protein (O’Dell and De Boland, 1976). There is evidence suggesting that the phytate-protein complexes are present not only in plants but they may also be formed de novo in the guts, thus compromising the utilization of dietary protein irrespective of its origin (Selle et al., 2000). Other possible consequences of phytate-protein interactions in reducing the utilization of dietary protein have been suggested such as the inhibi-tion of proteolytic enzymes by altering their pro-tein configuration (Singh and Krikorian, 1982) or increase of endogenous nitrogen losses (Ravindran et al., 1999). However, the results of experiments aimed at the study of the efficacy of microbial phytase for im-proving protein utilization in pigs were contradic-tory. Phytase has been reported by several authors to increase protein or amino acid digestibility and retention (Officer and Batterham, 1992; Mroz et al., 1994; Kemme et al., 1999a). Contrary to these observations, there are other studies which failed to demonstrate any significant effect of added phytase on protein utilization in pigs (O’Quin