Net energy reduction and intended slow starch formulation decreased fat deposition in broiler chickens offered conventional and reduced crude protein diets.

The drawbacks of reduced-crude protein (RCP) diets could include poor growth performance and increased fat deposition. Formulating diets with reduced net energy (NE) densities and slower starch digestion rates could mitigate fat deposition without compromising growth performance. Therefore, this study determined how different NE levels and starch digestion rates influence the performance in broilers offered 205 and 175 g/kg CP grower and 190 and 160 g/kg CP finisher diets. The study comprised a 2 × 2 × 2 factorial arrangement with two NE levels (conventional and 75 kcal/kg reduction), two starch digestion rates (with and without field pea inclusion), and two CP levels (standard and 30 g/kg reduction). Each dietary treatment had 7 replicates with 6 birds per replicate, totaling 336 off-sex male Ross 308 broiler chickens over feeding phases of 11-25 and 25-35 d. Conventional NE during d 11-25 and 25-35 periods were 2350 and 2400 kcal/kg, respectively; while the standard CP were 205 and 190 g/kg, respectively. Overall (d 11 - 35), RCP diets compromised growth performance and increased fat deposition (13.8 versus 11.6 g/kg, P< 0.05). Reducing dietary NE significantly reduced relative fat-pad weights by 9.02% (12.1 versus 13.3 g/kg), as did slowly digestible starch (SDS) by 7.58% (12.2 vs 13.2 g/kg). At day 35, the birds' abdominal fat pad was positively correlated ileal starch: protein disappearance rate ratio (r = 0.610; P< 0.001) and breast weight was negatively with ileal starch: protein disappearance rate ratio (r = - 0.485; P< 0.001). In conclusion, moderate reductions in dietary NE can be successfully incorporated into reduced-CP diets to reduce fat pad deposition; however, it remains challenging to maintain growth performance in RCP diets.