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Abstract

The use of antibiotic growth promoters (AGPs) in poultry began in the mid-20th century and became widespread. However, concerns over the emergence of antibiotic resistance have led to increasingly strict regulations in the EU, US, and Canada, and have driven a search for alternative solutions. Antimicrobial peptides (AMPs) are short and mostly cationic biomolecules. Some AMPs show antimicrobial activity and are promising alternatives to conventional antibiotics in the poultry industry. Yet their safety, delivery, and efficacy under commercial production environments remain underexplored. In this study, I aimed to evaluate the safety, growth promoting effects, delivery feasibility, stability, and selective antimicrobial activity of several AMPs through in vivo and in vitro experiments. Selected AMPs (TeRu4, TeBi1, PeNi4, and CLIB_denovo6) were administered via in ovo injection at 10 or 20 µg/egg and tested in pen trials, assessing hatchability, survival probability, and production parameters. Moreover, I assessed the stability of these AMPs in drinking water conditions of farms and assessed their antimicrobial spectra. All AMPs were well-tolerated, with hatchability, survival, and production parameters for most AMPs comparable to controls. There were some AMP- and sex-specific effects, suggesting context-dependent responses. Notably, TeRu4 and CLIB_denovo6, both at 20 µg/egg, significantly increased the survival probability of female birds compared to the controls by approximately 4.9 and 5.7%, respectively, by day 35. Moreover, TeBi1 at 20 µg/egg significantly increased the survival probability of male birds compared to the control by approximately 6.6% by day 35. All AMPs demonstrated high stability in tap water and TeRu4 had selective activity against Gram-negative pathogens, supporting its potential for targeted use. These findings support the feasibility of AMP-based interventions in poultry but highlight the need for standardized protocols and mechanistic studies. Next steps should focus on validating these outcomes in larger, production-scale settings.