Effects of beta-mannanase supplementation in combination with low and high energy dense diets for growing and finishing broilers

A total of 540 and 1-d-old male Ross 308 broilers (BW=43±1 g) were randomly divided into 4 treatments (9 replicates/treatment, 15 chicks/replicate) by their BW. This experiment lasted for 28-d and there were 2 phases, starter (0 to 14 d) and finisher (15 to 28 d). The experiment was a 2×2 factorial arrangement with two levels of metabolizable energy [low energy=12.34 (starter) and 13.08 MJ ME/kg (finisher); high energy=12.66 (starter) and 13.39 MJ ME/kg (finisher), the differences in dietary energy were based on differences in the content of tallow and maize] and two levels of β-mannanase (MAN) (0 and 0.04%). During starter phase, the effect of MAN and high energy were observed to increase (P<0.05) BW gain and decrease (P<0.05) feed conversion ratio. Chicks consumed high energy and MAN diets improved (P<0.05) BWG, whereas only effect of MAN was found to improve feed efficiency in overall phase. There was a significant interaction between mannanase and dietary energy content with respect to BWG (P=0.014) and FCR (P=0.042). The apparent total tract digestibility of dry matter and energy were improved (P<0.05) by the high energy density and MAN alone at end of experiment. There was a significant (P=0.045) effect of MAN with respect to meat lightness. Feeding chicks with high energy and MAN supplementation alone were shown to have higher (P<0.05) relative breast meat weight. There was a significant interaction between mannanase and energy regarding the breast meat yield (P=0.024). The breast meat of chicks fed high energy diet had greater (P<0.05) concentration of C16:0 and C18:0 and total saturated fatty acids and lower (P<0.05) linoleic acid (18:2n-6), and total unsaturated fatty acids than in low energy diet. In conclusion, the results indicated that the β-mannanase supplementation in low and high energy diets can improve body weight gain, feed conversion ratio, nutrient digestibility, and relative breast meat weight and decrease the LDL-C in serum.