Researchers at Penn State University have discovered that the age of broiler chickens has a more significant impact on their resistome — the collection of genes that contribute to antimicrobial resistance — than the type of feed additives they receive. This finding, published in the journal Poultry Science, comes from a study involving 320 broiler chickens that were fed one of four different diets: a standard diet with no additives, a diet containing antibiotics, one with essential oils, and another with a probiotic. To analyze the resistome, scientists collected fecal samples from the chickens at three key stages of development: 1 day, 10 days, and 21 days old. Using DNA sequencing, they identified a total of 823 unique antimicrobial resistance genes. The results showed that the resistome of a 1-day-old chick was quite different from that of a 10-day-old chick, and it changed again by day 21. This shift in the resistome is linked to the natural evolution of the gut microbiome as the chickens grow. Over time, new bacteria colonize the gut, others disappear, and some become more dominant, altering the types and abundance of resistance genes. While the study does not claim that feed additives have no effect on antibiotic resistance in poultry, it suggests that under the specific conditions of the experiment, the natural changes in the chickens’ gut microbiomes had a greater influence on the presence and types of resistance genes than the dietary treatments. This insight could help guide future research and practices in poultry farming, focusing on how age-related changes in gut health might influence antimicrobial resistance. The research team used the high-performance Roar Collab cluster, a computational resource at Penn State’s Institute for Computational and Data Sciences, to analyze the large datasets generated by DNA sequencing. This advanced computing power allowed for a detailed and accurate examination of the resistome dynamics in the broiler chickens.