Effects of feed form and xylanase supplementation on metabolizable energy partitioning in broiler chicken fed wheat-based diets

An experiment was conducted to investigate the effects of feed form and xylanase supplementation on the growth performance, energetic efficiencies, energy partitioning, and nitrogen (N) balance of Ross 308 male broilers fed wheat-based diets. The experiment was conducted as a 2 x 2 x 5 factorial arrangement with 2 levels of feed forms (mash or pellets) and xylanase (0 or 500 mg/kg), and five feeding levels (ad libitum, 85%, 70%, 55%, and 40% of ad libitum intake). Each of the 20 dietary treatments was fed to 5 replicate pens (5 birds/pen) from 22 to 42 days of age. A significant interaction between feed form and xylanase on was observed for average daily feed intake and heat production (p < 0.01). Pelleting and dietary supplementation with xylanase increased average daily gain and feed conversion ratio but decreased (p < 0.05) average daily feed intake. Broilers fed xylanase-supplemented diet ingested and pelleted diet retained more than in those fed the mash form or the diet without xylanase. Xylanase and pellets decreased (p < 0.01) heat production and metabolizable energy intake (MEI), but increased retained energy (p < 0.05). The birds fed xylanase also needed less MEI per gram of N retained than those fed the diets without enzyme (p < 0.01). Estimation of both metabolizable and net energy requirements for maintenance as a function of BW0.75 showed that requirements for broilers fed pelleted diet and xylanase-supplemented diet were lower than in those fed mash form or the diet without xylanase (p < 0.01). The higher energetic efficiencies for retention were estimated in the birds offered pelleted and xylanase-supplemented diets compared with the values determined for those fed the diet with mash form or the diet without xylanase (p < 0.05). The efficiency of energy utilization for protein for birds fed xylanase-supplemented diets was higher (p < 0.01) than those fed diets without xylanase, and fat deposition for broilers fed the pelleted diet was greater than those fed the mash diet (p < 0.01). Because MEI for maintenance requirements represents a large portion of the MEI, the results from this experiment could be considered in calculation of energy requirements for finishing broilers fed wheat-based diets.