The Impact of Feed Additives and Calcium Concentration and Source on Broiler Performance, Nutrient Utilization, and Intestinal Health Under Different Disease States

Abstract

Optimizing broiler nutrition is essential for maintaining performance, enhancing nutrient utilization, and supporting intestinal health, especially when birds face various disease challenges. The reduction or removal of antibiotic growth promoters (AGP) in broilers has presented additional challenges for nutritionists, necessitating the development of alternative feeding strategies that sustain broiler performance and health while minimizing feed costs. These feeding strategies should aim to replicate performance outcomes previously achieved with AGP, though this remains difficult due to the complex mode of action of AGP. The present research explored two nutritional strategies to address AGP removal in broiler feeding: (1) feed additives and (2) diet manipulation. Feed additives like phytase and butyrate may help to alleviate the negative effects of AGP removal on broiler growth. Phytase, an exogenous enzyme, is commonly included in broiler diets to degrade phytate and enhance phosphorus (P) digestibility. Butyrate, an organic acid, improves intestinal health by modulating the microbiota and providing energy to intestinal epithelia. To evaluate the first nutritional strategy, broilers were provided with 1 of 9 treatments that included varying levels of phytase, calcium butyrate (CB), and bacitracin methylene disalicylate (BMD). Supplementing BMD increased early broiler body weight (BW), particularly when combined with 1,500 FTU/kg of phytase, but not with 500 FTU/kg. Depending on phytase inclusion, broilers fed a diet with CB exhibited similar BW compared to those fed BMD. Additionally, phytase at 1,500 FTU/kg enhanced fat and P digestibility, and apparent ileal digestible energy (AIDE). Intestinal physiology and cecal microbiota composition were influenced by CB and BMD, with changes in villus height, tight-junction gene expression, and cecal microbial evenness, depending on dietary phytase concentrations. These findings highlight the complex interactions between feed additives and their potential to modulate broiler performance and intestinal health. The second nutritional strategy involved manipulating dietary components, such as calcium concentration and limestone particle size, to help mitigate performance and mortality impacts from enteric diseases. Broiler diets are often unintentionally formulated with excess calcium, which may exacerbate necrotic enteritis by supporting NetB and α-toxin activity, leading to reduced nutrient utilization and compromising broiler health. Excess calcium can also increase calcium-phytate formation, resulting in undigested nutrients that become available to intestinal microbiota, potentially promoting proliferation of pathogenic bacteria. To evaluate this strategy, broilers were assigned to 1 of 7 treatments, including an unchallenged control and 6 enterically challenged groups fed diets with varying limestone particle sizes and calcium concentrations. The enteric challenge reduced broiler performance without affecting mortality. Reducing dietary calcium by 0.10 percentage units from recommended levels maintained broiler performance, tibia mineralization, and AIDE during an enteric challenge. Furthermore, calcium and P digestibility increased when dietary calcium was reduced. However, feed conversion and nutrient utilization responses varied depending on limestone particle size. Understanding the interaction between dietary calcium and limestone particle size could help to mitigate the impact of enteric diseases. Ultimately, to develop sustainable solutions that enhance broiler growth and health, broiler nutritionists must continue exploring AGP alternatives and further understand interactions between feed additives and dietary components.