ABSTRACT
The effect of applying an energy and nutrient matrix to a wheat-corn-soybean meal-based diet supplemented with a novel consensus bacterial 6-phytase variant (PhyG) and xylanase-ß-glucanase on growth performance, bone mineralization, carcass weights, feed costs, and carbon footprint was evaluated. A randomized complete block design (3,300 Ross 308 mixed-sex birds; 60 pens, 12 pens per treatment) tested 5 treatments: 1) a positive control diet (PC), containing 0.92, 0.84, 0.71% Ca and 0.43, 0.38, 0.30% digestible P during 1 to 10, 11 to 21, and 22 to 32 d of age, respectively; 2) a negative control reduced in Ca, digestible P, digestible AA, ME, and Na by phase based on the PhyG dosing regimen (NC1); 3) NC1 supplemented with PhyG at 2,000, 1,500, and 1,000 FTU/kg by phase (NC1+PhyG); 4) as NC1 but additionally reduced in ME (NC2); and 5) NC2 supplemented with PhyG as in 3) plus 1,220 U/kg of xylanase and 152 U/kg of ß-glucanase (NC2+PhyG+XB). Final (d 32) BW, overall (0-32 d of age) ADFI, FCR, d 10 and 32 tibia ash and carcass part weights were reduced or impaired (P < 0.05) in NC1 and NC2 vs. PC (d 32 BW -477 g/bird (23.4%) and -422 g/bird (20.7%), respectively). Growth performance (all measures, all phases) was improved and tibia ash (at 10 and 32 d of age), total carcass thigh, breast and leg weights were increased (P < 0.05) in NC1+PhyG vs. NC1, and NC2+PhyG+XB vs. NC2. Overall growth performance outcomes in NC1+PhyG and NC2+PhyG+XB were not different (P > 0.05) from the PC. Total feed cost and carbon footprint per kilogram BW gain (BWG) were reduced (P < 0.05) vs. PC in NC2+PhyG+XB [-0.052 and -376 g CO2 eq./kg BWG, respectively] and NC1+PhyG [-0.038 and -260 g CO2 eq./kg BWG, respectively]. The results validated the nutrient matrices in the test diets and highlighted a potential feed cost and environmental sustainability benefit which was greatest when the enzymes were applied in combination.
