Does modern broilers need less energy for better growth and intestinal development?

The current study was carried out to evaluate the response of broiler chicks to dietary energy. In total 11,400 day-old Ross-308 chicks (95 males and 95 females per pen) were placed in the study for 42 days. Hatchlings were randomly distributed to 6 dietary treatments with 10 replicates. Aviagen metabolisable energy (ME) recommendation for Ross 308 was served as a positive control (PC) and other treatments were adjusted to 101.25, 98.75, 97.50, 96.25 and 95% of PC. Birds had free access to water and pellet feed. Body weight (BW), Feed intake, feed conversion ratio (FCR), carcass yield and jejunal morphometric analysis were determined per replicate. Feeding the birds with 1.25% higher ME than PC did not result in any improvement in BW, FCR, mortality and carcass parameters. Significant linear improvement was observed at starter period for BW and FCR with the reduction of dietary ME (p < 0.05). There was no significant impairment in final BW with the reduction of ME up to 5.0%. Whole period FCR reduced by 0.009, 0.022, 0.014, 0.037 points by lowering ME by 1.25, 2.5, 3.75 and 5%, respectively (linear, p < 0.05). Carcass yield, abdominal fat and pancreas weights were not significantly influenced (p > 0.05). However, significant improvement in villus height, surface area (quadratic and cubic, p < 0.05), and villus width (quadratic, p < 0.05) were observed with 2.5 and 3.75% reduction of dietary ME. Dietary treatments had no significant effect on liver haemorrhagic lesion score. The results of the current research suggest that the optimum level of dietary energy level of modern broilers may be lower than the one recommended by the primary breeders. Lowering dietary energy density up to 5% leads to 0.03 points reduction in FCR without any negative effect on BW.