The Effects of Replacing Synbiotics and macroalgae Sargassum with Oxytetracycline on Performance, Carcass Characteristics, Intestinal Morphology and Blood Serum Lipid Parameters of Broiler Chickens

Introduction: Antibiotics have been used for many years in animal production to treat infectious diseases and as growth promoters. However, the misuse of antibiotics causes problems such as bacterial antibiotic resistance. Also, the possible accumulation of antibiotic residues in livestock products is risky for consumers. After the ban on the use of antibiotic growth promoters in 2006, there was a need to use substitutes in animal feed to replace antibiotics. These alternatives include prebiotics, probiotics, phytobiotics and synbiotics. Probiotics are live microorganisms that, when consumed in sufficient amounts, have beneficial effects on the host by creating a microbial balance in the gut. The purpose of probiotics is to create a competition between the species that are naturally present in the intestinal flora of broilers. The most important advantage of probiotics is that they do not remain in animal products. Prebiotics are feed compounds that are not digested by the host when consumed but can support beneficial bacteria. These compounds are short-chain carbohydrates such as non-digestible oligosaccharides that cannot be digested by animal enzymes. Compounds containing prebiotics and probiotics used in nutrition are called synbiotics. Phytobiotics include a wide range of plant-derived products with bioactive compounds. Plant feed additives (PFAs) are widely effective in improving gut health, increasing digestibility and thus growth performance. These bioactive compounds include secondary metabolites (phenolic and flavonoid). In recent years, various marine organisms have been considered as valuable biological compounds for livestock. Marine algae, due to a wide range of bioactive components such as flavonoid, carotenoid, phenolic compounds, tocopherol, peptide and various sulfated and carboxylated polysaccharides such as alginate and fucoidan with antibacterial, antifungal and antiviruses have beneficial effects on health. Brown macroalgae such as Sargassum angustifolium have beneficial effects on health due to a wide range of bioactive components such as fucoidan, fucose sulfate and polysaccharides. Also, this group of algae is a rich source of sodium alginate oligosaccharides.Materials and Methods: The present study was conducted in the form of a completely randomized design, lasted for 42 days at the Ali Abad Kamin research farm of the Fars Agricultural and Natural Resources Research and Education Center, Shiraz, Iran. A total of 240 Ross 308 broi