The Effects of Phytase on Performance, Serum Mineral Levels, Enzyme Activities and Immune Function of Broilers Fed Nutritionally Marginal Diets

2 Abstract: An experiment was conducted to study the effect of microbial phytase (Natuphos 10000) supplementation in chicks fed Nutritionally Marginal Diets on performance, plasma minerals, serum enzyme activities and humoral immunity. Treatments were replicated with 4 pens of 12 chicks each. Diets were Corn-wheat-soybean meal based with the same nutritional specifications, differing only in the concentration of Ca and nonphytate P (Ca-nPP). The treatments were: 1) adequate-Ca-nPP diets (CTL+); 2) Low-Ca-nPP diets (CTL-); 3 to 5 = diet 2 plus 600, 800, or 1000 phytase units (FTU) /kg of diet from Natuphos. The low-Ca-nPP diets caused a negative effect on feed consumption compared to the CTL+ diet. Performances of chicks fed with low-Ca-nPP diets and phytase were comparable to those obtained with the low-Ca-nPP and adequate-Ca-nPP diets. By decreasing Ca-nPP levels in the diet, plasma Ca concentrations, aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) activity were reduced and alkaline phosphatase (ALP) activity increased. Phytase supplementation increased plasma Ca level and serum AST activity and reduced ALT, ALP and LDH activities. Antibodies against Newcastle disease virus vaccine were enhanced of 14 to 42-d-old broilers in the low Ca-nPP diets with phytase addition. Increasing the phytase dose to 1,000 FTU /kg did not improve immune function further than 800 FTU /kg. The results suggest that application of phytase in nutritionally marginal diets could enhance antibody titer of 14- to 42-d-old broilers, suggesting that both deficient in Ca-nPP and phytase may have a role in immune competence.