Abstract
This study evaluated the effects of different dietary levels of sunflower hulls (SFH) as an insoluble fiber source on growth performance, nutrient digestibility, intestinal morphology, cecal microbial populations, litter quality, and digesta transit time in broiler chickens fed varying levels of crude protein (CP). A total of 360 one-day-old broiler chicks were randomly assigned to a 3 × 2 factorial design comprising three SFH levels (0, 20, and 40 g/kg) and two CP levels (normal and 10% reduced). Broilers fed diets containing 40 g/kg SFH combined with normal CP exhibited the most favorable feed conversion ratio (FCR), whereas the poorest FCR was observed in those reared on the fiber-free, low-CP diets. Dietary inclusion of SFH progressively enhanced the apparent ileal digestibility (AID) of nitrogen, organic matter, and ether extract. Furthermore, improvements in villus height, width, and surface area in both the duodenum and jejunum were observed, as levels of SFH increased. These morphological advancements were accompanied by a significant shift in the cecal ecosystem, characterized by an increased population of beneficial Lactobacillus spp. Additionally, the inclusion of 40 g/kg SFH effectively reduced litter nitrogen content. In conclusion, these findings suggest that moderate inclusion of sunflower hulls, particularly at 40 g/kg, has the potential to enhance digestive efficiency, support gut health, and modulate microbial populations in broiler chickens. However, its efficacy in mitigating the performance drawbacks of reduced-crude protein diets warrants more cautious optimization depending on the specific dietary balanced amino acid profiles.