Effects of physical feed form of the diets on growth performance, intestinal microflora and morphology, and litter quality in broiler chickens

Introduction: In recent years, the poultry industry has encountered several challenges. One critical yet often overlooked issue is the relationship between feed texture and litter quality, which significantly impacts locomotive problems and carcass quality. Nutritional factors such as energy and protein levels, minerals, feed texture, and dietary restrictions play a crucial role in influencing litter moisture, litter quality, carcass characteristics, and the condition of bird feet. Litter serves as a conducive environment for microbial growth and ammonia production. Effective management of litter moisture and ammonia emissions is vital for disease prevention and enhancing air quality in poultry houses. Ammonia production is a major concern in enclosed poultry systems, originating from the microbial breakdown of uric acid in excreta. The emission rate of ammonia gas from poultry litter is influenced by pH, moisture content, temperature, ventilation, ammonia and uric acid levels in excreta, litter type, stocking density, and bird age. Different feed processing methods and structural changes impact bird performance, intestinal microbial diversity, intestinal health, digestion, intestinal content viscosity, enzyme activity, and pH levels. In the first week post-hatching, the small intestine experiences rapid growth, with increased villi height and crypt depth, enhancing nutrient digestion and absorption. This growth is accompanied by the stabilization of gut microbiota. The balance between pathogenic and non-pathogenic bacteria is crucial in determining disease occurrence. The type, structure, quality, and quantity of diet significantly influence intestinal cell growth, nutrient utilization, and bacterial species composition, particularly at the digestive system's end. Over 640 microbiota species in the digestive system contribute to digestive health and microflora balance. Research indicates that the ileum's microbial profile in broiler chickens affects intestinal performance and, subsequently, nutrient digestion and absorption. This study aimed to explore the effects of different feed textures (mash, crumble, pellet, and extruded) on intestinal histology, microbiota, and litter quality in broiler chickens.
Materials and methods: In this study, 480 one-day-old male Ross 308 broiler chickens, each weighing approximately 36 grams, were used. The chicks were sourced from Navaid Morgh Gilan Company in Rasht, Iran. Before their arrival, experimental diets were prepared and placed in feeding trays, while water was provided using siphon and nipple drinkers. The diets were offered in four physical forms: mash, crumble, pellet, and extruded, formulated to meet the nutrient guidelines for Ross 308. At the experiment's conclusion, the chickens were weighed, and their feed consumption was recorded. Body weight gain (BWG), feed intake (FI), feed conversion ratio (FCR), and mortality rate were calculated at the end of the rearing period. The birds were slaughtered on day 42. To evaluate the impact of feed physical form on intestinal microbial flora, contents from the duodenum, jejunum, and ileum were collected to count Escherichia coli, Lactobacillus, and total coliforms. On days 21 and 42, litter from all pens was examined. Samples were collected from five areas of each pen's litter (four corners and one center sample) and analyzed in the laboratory. For moisture measurement, approximately 50 grams of litter were dried in an oven at 105 °C until a constant weight was achieved, determining moisture content through weight loss. Post-slaughter, samples from the duodenum, jejunum, and ileum were preserved in a 10% formalin solution. After 72 hours of tissue fixation, dehydration was performed using increasing concentrations of ethanol followed by xylene treatment. Samples were then embedded in paraffin and sectioned into 5-6 μm slices, stained with hematoxylin and eosin (H&E). Villus length was measured from top to base, and width was recorded at the midpoint. Crypt depth was measured from the villus base to the end of the mucous layer. The villus length to crypt depth ratio and surface area were calculated, along with the thickness of the lamina propria and muscularis mucosae. Statistical analysis was conducted using SAS software with the GLM procedure in a completely randomized design.
Results and discussion: The study results indicated that growth performance was significantly affected by the form of feed (P<0.01). Chicks fed with extruded feed throughout the rearing period demonstrated improved performance compared to other treatments (P<0.05). The highest level of anaerobic bacteria in the litter at 35 days was found in the pellet group (P<0.05). At 21 days, the greatest litter moisture was associated with crumbled feed in the starter diet and pellets in the grower and finisher diets. The lowest weights of the ileum and jejunum were observed in chicks fed extruded feed throughout the rearing period (P<0.05). The maximum villus height in the jejunum was noted with crumbled feed in the starter diet and extruded feed in the grower and finisher diets, as well as with pellets throughout the period. Additionally, using crumbled feed in the starter diet and pellets in the grower diet resulted in the maximum villus width.
Conclusions: The study indicated that the physical form of diets significantly influences growth performance, digestive efficiency, nutrient absorption, intestinal histology, litter pH and moisture, and intestinal bacterial populations. Birds fed extruded feed throughout the rearing period achieved the highest BWG. The lowest FCR was observed in chicks that consumed crumbled feed during the starter phase and extruded feed during the grower and finisher phases; however, these differences were not significant compared to birds consistently fed extruded feed. Pellet and extruded diets negatively impacted bedding moisture compared to mash diets, potentially increasing the risk of hock joint burns and lameness in broiler chickens. Therefore, careful attention must be given to litter management, considering the type of feed used.