Abstract
Two experiments were conducted to evaluate extra-phosphoric effects of phytase and nutrient density on growth performance, meat yield, and hypothalamic appetitive hormone expression and catecholamine concentrations of broilers. Experiment 1 determined differences of digestible amino acid concentrations and AMEn using 256 Yield Plus × Ross 708 broilers (32 cages, 8 birds/cage) fed diets without or with 4,500 phytase units (FTU)/kg inclusion (16 reps/treatment). In Experiment 2, 832 Yield Plus × Ross 708 broilers (32 pens; 26 birds/pen) were provided diets in a 2 × 2 factorial arrangement consisting of 2 nutrient contents (without or with increased density) and 2 phytase inclusions (0 or 4,500 FTU/kg). Increased nutrient density was formulated to contain 0.007, 0.015, 0.013, 0.021, 0.024%, and 61 kcal/kg higher digestible SAA, Lys, Thr, Val, Ile, and AMEn (from Experiment 1) respectively, compared with the control diet. Growth performance was determined at 14, 28, and 40 d of age and carcass characteristics at 41 d of age. At 43 d of age, plasma inositol, hypothalamic appetitive hormone expression, and catecholamine concentrations were determined from 4 birds/pen. Additive effects of phytase inclusion and increased nutrient density resulted in the lowest (P < 0.05) feed conversion from 1 to 40 d of age and the heaviest (P < 0.01) breast meat weights among dietary treatments. Phytase addition numerically increased feed intake (P = 0.06) and BW gain (P = 0.051) compared with birds fed diets without phytase from 1 to 40 d of age. Plasma inositol and dopamine concentrations were 2.3- and 1.2-fold higher (P < 0.01), respectively, in broilers fed phytase-added diets than birds fed diets without phytase inclusion. However, mRNA expression of neuropeptide Y, agouti-related peptide, proopiomelanocortin, cholecystokinin A receptor, ghrelin, and serotonin concentration were not different (P > 0.05) among treatments. These data indicated additive effects of phytase supplementation and increased nutrient density on growth performance and meat accretion of broilers. However, the influence of phytase on feed intake warrants future research.