This experiment was conducted to evaluate the combination effect of low dietary non-phytate phosphorus (NPP) concentrations, phytase (PHY) levels, and 25-hydroxycholecalciferol (25-OH-D 3 ) levels on the growth performance and meat quality of broilers. Two levels of NPP, two levels of PHY, and two levels of 25-OH-D 3 resulted in a 2×2×2 factorial arrangements, with eight treatments (TRT). The birds on TRT 1-4 were fed diet 1 (NRC NPP was reduced by 0.1) and the birds on TRT 5-8 were fed with diet 2 (NRC NPP was reduced by 0.2). Each diet was mixed with different levels PHY and 25-OH-D 3 . Performance and meat quality parameters were measured. Results showed that during entire experiment the most advantageous effects were obtained with TRT 3 (NRC NPP reduced by 0.1 + 600 U/kg phytase + 34.5µg/kg 25-OH-D 3 ) and TRT 4 (NRC NPP reduced by 0.1 + 600 U/kg phytase + 69µg/kg 25-OH-D 3 ). The lowest body weight gain (BWG) and feed intake(FI) were observed with TRT 5 (NRC NPP reduced by 0.2 + 300 U/kg phytase + 34.5µg/kg 25-OH-D 3 ). Lowering NRC NPP by 0.1 to 0.2 significantly reduced weight gain (WG) (p< 0.05) and FI (p< 0.05) during the starter phase (ST), while during grower phase (GF) lowering NRC NPP by 0.1 to 0.2 did not affect WG (p>0.05) and produced small decrease in FI. BWG, FI and feed conversion ratio were not influenced (p>0.05) by different PHY or 25-OH-D 3 levels. In addition, the meat color, pH, and shear force were not affected by the different NPP, PHY or 25-OH-D 3 levels.

2In pig production, insufficient feed digestion causes excessive nutrients such as phosphorus and 3 nitrogen, which are then released to the environment. To address the issue of environmental 4 emissions, we have established transgenic pigs harboring a single-copy quad-cistronic transgene 5 and simultaneously expressing three microbial enzymes, β-glucanase, xylanase, and phytase in the 6 salivary glands. All the transgenic enzymes were successfully expressed, and the digestion of non-7 starch polysaccharides (NSPs) and phytate in the feedstuff was enhanced. Fecal nitrogen and 8 phosphate outputs were reduced by 23%-46%, and growth rate improved by 23.4% (gilts) and 9 24.4% (boars) when the pigs were fed on a corn and soybean-based diet and high-NSP diet. The 10 transgenic pigs showed a 11.5%-14.5% improvement in feed conversion rate compared to the 11 age-matched wild-type littermates. These findings indicate that transgenic pigs are promising 12 resources for improving feed efficiency and reducing nutrient emissions to the environment.