Growth Performance of Growing Pigs Fed Crude Protein-Adequate or Deficient, Low Phosphorus Diets with Graded Levels Of Phytase

Nitrogen and phosphorus are the nutrients that are potential environmental pollutants when excessive quantities are applied to soils (Jongbloed and Lenis, 1998). These nutrients are excreted as a consequence of normal metabolic processes, but dietary excesses lead to increased manure excretion. Exogenous phytase (P T) as a dietary additive is widely accepted as an effective strategy for reducing manure P excretion by pigs. There have been conflicting reports as to the efficacy of PT for improving N or amino acid digestibility and retention. Phytic acid may form insoluble complexes with proteins (Cheryan, 1980) and inhibit proteolytic enzymes (Singh and Krikorian, 1982), which can lower protein digestion. Phytase has been reported to increase digestibility (Mroz et al., 1994; Kemme et al., 1999; Zhang and Kornegay, 1999) and retention (Keteran et al., 1993; Mroz et al., 1994; Li et al. 1998) of protein and/or amino acids in pigs. Keteran et al. (1993) reported that the addition of PT to the diet of growing pigs led to an increased N retained as a percent of intake and protein deposition in skeletal muscle, but found no effect on the apparent digestibility of protein. The effect of PT on amino acid digestibility appears to be more accurately determined at the terminal ileum, rather than in the feces. If the main objective, however, is to determine the effect of PT on overall utilization of N, a balance study would be the more appropriate approach. A growing pig retains only 30 to 35% of the total dietary N and P ingested (Jongbloed and Lenis, 1992). Pigs in the growing phase account for approximately 75% of the total P excreted in the production cycle (Poulsen et al., 1999). Feeding strategies aimed at reducing N and P excretion by reducing dietary crude protein and inorganic P along with PT supplementation may maximize the efficiency of utilization of both N and P. The objective of this study was to determine the effects of graded levels of PT added to reduced protein, low P diets on N and P balance and growth performance of growing pigs.