ABSTRACT
The effects of phytate and phytase on broiler performance and cellular and humoral immunity was assessed by using 504 Cobb 500 female broilers fed nutritionally marginal diets. At 1 d of age, the chicks were randomly allocated to 6 treatments in a 2 x 3 factorial arrangement including 2 levels of phytate P (0.22 or 0.44%) and 3 dose rates of an Escherichia coli-derived phytase [0, 500, or 1,000 phytase units (FTU)/kg of feed]. Both low- and high-phytate diets were corn and soy based with the same nutritional specifications (AME 2,900 kcal/kg, CP 21.00%, Ca 0.78%, and nonphytate P0.28%), differing only in the concentration of phytate P. The immune status of birds was measured at 14, 21, and 28 d of age. The results revealed that phytase improved feed intake, BW, and feed conversion ratio (P < 0.05), whereas high dietary phytate depressed bird performance (P < 0.05). There was no interaction between phytate and phytase on bird performance. Feeding phytase increased the percentages of erythrocyte rosette-forming cells and erythrocyte-antibody complement cells by 3.03 and 1.83% at d 21, and by 2.76 and 2.20% at d 28, respectively (P < 0.05). The percentages of CD4(+)CD8(+) T lymphocyte subsets were also increased by phytase (P < 0.05), without affecting the ratio of CD4(+) and CD8(+). The levels of intestinal secretory IgA were improved with phytase at d 14, 21, and 28 (P < 0.05). Antibodies against Newcastle disease virus vaccine were enhanced at d 21 and 28 in the high-phytate diets with phytase addition (P < 0.05). Increasing the phytase dose to 1,000 FTU/kg did not improve immune function further than 500 FTU/kg. The results suggest that application of phytase in nutritionally marginal diets could enhance lymphocyte numbers and the seral and mucosal antibodies of 1- to 28-d-old broilers, suggesting that both phytate and phytase may have a role in gastrointestinal health and immune competence.
