Effects of physical feed form (mash, crumble, pellet and extruded) of the diets on growth performance, intestinal microflora and morphology and litter quality in broiler chickens

Introduction: The poultry industry has faced numerous challenges in recent years, many of which relate to litter quality, gut health, and feed efficiency. Various nutritional factors such as energy and protein levels, mineral content, feed physical form, and dietary restrictions significantly influence litter moisture, litter quality, carcass traits, and foot health. Among these, the relationship between feed physical form and litter quality has received relatively little attention, despite its potential link to locomotion problems, carcass defects, and economic losses. Feed processing methods such as mash, crumble, pellet, and extrusion markedly affect the feed’s structure, density, digestibility, viscosity, and digestive characteristics, thereby influencing gut health, microbial populations, nutrient utilization, feed intake, and growth performance. For example, pelleting reduces feed wastage, increases metabolizable energy density, and improves feed conversion ratio, whereas extrusion by applying heat, pressure, and moisture enhances starch and protein digestibility. Litter moisture creates a favorable environment for microbial proliferation and ammonia production, which is a major concern in closed poultry housing systems due to its negative effects on respiratory health. Ammonia emission from litter depends on factors such as pH, moisture, temperature, ventilation, ammonia and uric acid concentration, litter type, stocking density, and bird age. Moreover, feed physical form influences intestinal morphology such as villus height and crypt depth which can improve or impair nutrient absorption. These morphological changes also affect the stability and composition of the gut microbiota, a critical factor in disease prevention and nutrient utilization. Although several studies have investigated the effect of feed physical form on poultry performance, most focus on a single feed form, with limited research on combinations of feed physical forms across different growth phases. Therefore, this study aimed to evaluate the effects of different feed physical forms, including mash, crumble, pellet, and extruded—administered separately or in combination during starter, grower, and finisher phases, on growth performance, intestinal microbiota, intestinal histology, and litter quality in broiler chickens. Materials and methods: 480 one-day-old male broiler chickens of Ross 308 strain with an average weight of 36 gr were used. The chicks were supplied by Navaid Morgh Gilan Company (Rasht, Iran). Before the arrival of the chicks, experimental diets were prepared and distributed in feeding trays, also water was provided in siphon and nipple drinkers. The diets were supplied in four physical forms: mash, crumble, pellet, and extruded. Diets were formulated to meet the nutrient recommendations for Ross 308. At the end of the experiment, chickens were weighed and feed consumption was recorded. Body weight gain (BWG), feed intake (FI), feed conversion ratio (FCR), and mortality weight were calculated for at the end of rearing period. The birds were slaughtered on day 42. To assess the effects of feed physical form on the intestinal microbial flora, the contents of the duodenum, jejunum, and ileum were collected for counting Escherichia coli, Lactobacillus, and total coliforms. On days 21 and 42, the litter of all pens was examined. Litter samples were collected from five areas of the litter in each replication (four samples from corners and one sample from the center) and transferred to laboratory for analysis. To measure litter moisture, approximately 50 gr of litter sample was placed in an oven at 105 °C until a constant weight was reached, and the moisture content was determined by the weight loss method after drying. After slaughter, samples were taken from the duodenum, jejunum, and ileumand were placed in 10% formalin solution. After tissue fixation for 72 h, dehydration was done with increasing concentration of ethanol following xylene treatment. Then, samples were embedded in paraffin and sectioned into 5-6 μm slices. The tissue sections were stained with hematoxylin and eosin (H&E). The distance from the top to the base of the villi was measured as villus length. The width of the villi was reported from the middle of the villi as villus width. The distance between the base of the villi and the end part of the mucous layer was measured as crypt depth. The villus length to the crypt depth ratio and the villus surface area were calculated. The thickness of the lamina propria and muscularis mucosae was also measured. Statistical analysis was performed using SAS software in a completely randomized design with the GLM procedure. Results and discussion: The results showed that feed physical form significantly influenced growth performance (P<0.05). Chicks fed extruded feed throughout the rearing period had the highest feed intake and weight gain, while the lowest intake was in the mash diet group. No significant difference was observed between the extruded-only group and those receiving crumble in the starter and extruded or pellet in later phases for weight gain (P>0.05). Feed form also affected feed conversion ratio (FCR) (P<0.01), with the lowest FCR in chicks fed crumble in starter and extruded in later phases, but not significantly different from the extruded-only group. Mash diet showed the highest FCR. Feed physical form impacted relative weight and length of jejunum and ileum (P<0.05), but not duodenum. The lowest jejunum and ileum weight were in the extruded group. Feed form significantly affected intestinal microbiota composition and litter characteristics including moisture, pH, and bacterial counts (P<0.05). The highest villi height in jejunum was observed in groups fed crumble in starter and extruded in later phases or pellet throughout. Conclusion: Physical form of feed markedly affects broiler growth, nutrient absorption, gut morphology, microbiota, and litter quality. Extruded feed throughout rearing yielded highest weight gain, while combination of crumble starter and extruded later improved FCR without significant difference to extruded-only. Pellet and extruded feeds increased litter moisture compared to mash, potentially raising risks of leg problems. Thus, optimizing feed form along with litter management is crucial for improving performance and bird health.