Antibiotic free farms are increasing in the poultry sector in order to address new EU regulations and consumer concerns. In this pilot study, we investigated whether the efforts of raising chickens without the use antibiotics make any difference in the microbiome of poultry meat eaten by consumers. To this aim we compared the microbiomes characterizing caeca and the corresponding carcasses of two groups of chickens reared, one reared on a conventional farm and one on an antibiotic-free intensive farm. The results showed a clear separation between the taxonomic, functional and antibiotic resistant genes in the caeca of the birds reared on the conventional and antibiotic free farm. However, that separation was completely lost on carcasses belonging to the two groups. The antibiotic-free production resulted in statistically significant lower antimicrobial resistance load in the caeca in comparison to the conventional production. Moreover, the antimicrobial resistance load on carcasses was much higher than in the caeca, without any significant difference between carcasses coming from the two types of farms. All in all, the results of this research highlighted the need to reduce sources of microbial contamination and antimicrobial resistance not only at the farm level but also at the post-harvest one.

This research investigated the effects of different synbiotic administration programs on broiler productive performance and foot pad dermatitis (FPD). Molecular insights on caecal microbiota and plasma metabolomics were also performed. - A total of 1000 one-day-old male chicks were grouped by the synbiotic treatment. The synbiotic was either sprayed as gel droplets onto newly hatched chicks at the hatchery (100 g/10,000 birds) or supplemented in-feed during the entire rearing period (1000, 500, and 250 g/ton according to feeding phase), or both. Only the treatments’ combination produced significant results in comparison with the control group (untreated), improving feed conversion ratio from 14 to 29 d and in the overall period of the trial (1.570 vs. 1.509 and 1.643 vs. 1.596, respectively; p < 0.05) while lowering FPD occurrence at slaughter (17% vs. 5%; p < 0.05). These findings can be related to significant variations of caecal microbiota, like higher Firmicutes to Bacteroidetes ratio (with favorable implications for host’s energy-harvesting potential from the diet) and more beneficial microbial consortium presumably sustaining eubiosis. Overall, these results indicate that administering synbiotics through gel droplets at the hatchery combined to in-feed supplementation for the whole growing cycle positively affects broiler feed efficiency and welfare.

The aim of this study was to assess how raising chickens without the use of antimicrobials affects the microbiome of poultry carcasses. A total of 151 caeca and neck skin samples from chickens raised without antimicrobials were collected in the same slaughterhouse and submitted to shotgun metagenomic sequencing. Caeca were dominated by Bacillota and Bacteroidota, while carcasses by Pseudomonadota. The caeca microbiome was enriched in genes related to a proliferating and metabolically active microbial community. Carcass-associated microbiomes were enriched in functional genes linked to adaptation to nutritionally limited and oxidative environments. A significantly higher cumulative antimicrobial resistance gene abundance was detected in carcasses compared to caeca. Specifically, carcasses exhibited approximately 1.5 times more AMR genes, reflecting an increase of nearly 49%. While caeca showed enrichment of resistance determinants associated with Gram-positive anaerobic gut commensals, carcasses were characterized by a predominance of multidrug efflux systems and clinically relevant β-lactam resistance genes, commonly associated with environmental and opportunistic Gram-negative bacteria. In carcasses, carbapenem-associated genes, such as OXA-58-like and CphA, were detected. However, these genes have not been associated with carbapenemase-producing Enterobacterales. Overall, the findings of this study indicate that reducing antimicrobial resistance in food animal production systems extends beyond farm-level intervention. At present, the benefits of the interventions aimed at reducing antimicrobial resistance at farm level seem to be compromised during the post-harvest stages.