The effect of reduced calorie diets, with and without fat, and the use of xylanase on performance characteristics of broilers between 0 and 42 days

When decreasing the energy value of broiler diets, nonstarch polysaccharide degrading enzymes, such as xylanase, are often used. In doing so, they are assigned an energy value and considered to contribute energy to the diet. The aim of this study was to determine the effect of decreasing energy in a broiler diet by 100 kCal/kg on performance and whether the expected drop in performance could be recovered with the use of xylanase. Two formulations were used to provide decreased energy diets, both with and without supplementary fat. Six hundred 1-d-old male Cobb broilers were placed in a 2 x 3 full factorial design in 5 randomized complete blocks. The treatments were enzyme dose at 0 or 16,000 U/kg, and the 3 different diets [positive control (PC), negative control 1, without fat (NC1), and negative control 2 with fat (NC2)]. At no point were there any interactions between diet type and enzyme inclusion; where there was an effect of xylanase, it was consistent regardless of the diet type. There was a significant effect of diet type on feed intake between d 0 to 35; NC1 and NC2 had significantly increased feed intake compared with the PC (P = 0.006). The feed conversion ratio was significantly increased in birds fed the negative control diets during 0 to 35 d and 0 to 42 d (P = 0.003 and P = 0.002, respectively). However, feed conversion ratio was significantly improved by the addition of enzyme during periods 0 to 35 d and 0 to 42 d. There were no significant main effects between d 0 and 21 (all responses P > 0.1). Liveability was not affected by any of the treatments (P > 0.1). Decreasing energy in broiler diets results in worsened performance. The use of xylanase may improve feed conversion ratio. The use of some fat may help, so the whole diet composition should be considered in conjunction with enzyme dose to achieve the best advantage.