Effects of Dietary Net Energy/Lysine Ratio and Sex on Growth Performance, Digestive Organ Development, and Cecal Microbiota of Broiler Chickens.

This study aimed to investigate the effects of the net energy (NE) and lysine ratio in low-protein diets on growth performance, intestinal development, and cecal microbiota of male and female broilers. A 4 × 2 factorial design was used with lysine levels at 1% and 1.5%, and net energy levels at 8.93 MJ/kg and 9.76 MJ/kg were used to form four diets with net energy/lysine ratios: Group I (8.93), II (5.95), III (9.76), and IV (6.50), respectively. A total of 960 AA broilers at age of 1 d were selected; then, 480 male and 480 female broilers were randomly divided into four groups, with eight replicates per group and 15 birds per replicate. The trial lasted for 17 days, with slaughter tests conducted separately at d 7 and 17 to measure growth performance and slaughter performance. The results are as follows: (1) At d 17, broilers in high NE/lysine groups had significantly higher final weights and average daily gain compared to other groups ( < 0.01), with males weighing more than females. (2) High NE/lysine ratios (8.93 and 9.76) significantly increased the relative lengths of the jejunum and ileum from d 1 to 17 ( < 0.05). At d 7, female broilers had greater relative lengths of the duodenum, jejunum, and ileum compared to males ( < 0.05, < 0.05, and < 0.01), while at d 17, male broilers had greater relative lengths of the duodenum and ileum than females ( < 0.01 and < 0.05). (3) At d 7 and 17, the villus height to crypt depth ratio in male broilers was significantly lower than that in females ( < 0.05). There was an interaction effect between NE/lysine ratios and sex on intestinal morphology. (4) High NE/lysine ratios (8.93 and 9.76) resulted in higher levels of Firmicutes and Bacteroidetes. Male broilers had higher levels of Firmicutes and Verrucomicrobia compared to females. Therefore, when lysine was at an appropriate level, a high NE/lysine ratio was more conducive to the growth and development of broilers through improving intestinal development and microbiota abundance. Female broilers showed faster intestinal development at the early age but weaker absorption capacity, while males showed dominance in intestinal length development. There were differences in characteristic gut microbiota between male and female broilers, with males having a higher abundance of energy metabolism-related microbiota.