Gut microbiota and its relationship to animal health and productivity in commercial broiler chickens has been difficult to establish due to high variability between flocks, which derives from plenty of environmental, nutritional, and host factors that influence the load of commensal and pathogenic microbes surrounding birds during their growth cycle in the farms. Chicken gut microbiota plays a key role in the maintenance of intestinal health through its ability to modulate host physiological functions required to maintain intestinal homeostasis, mainly through competitive exclusion of detrimental microorganisms and pathogens, preventing colonization and therefore decreasing the expense of energy that birds normally invest in keeping the immune system active against these pathogens. Therefore, a “healthy” intestinal microbiota implies energy saving for the host which translates into an improvement in productive performance of the birds. This review compiles information about the main factors that shape the process of gut microbiota acquisition and maturation, their interactions with chicken immune homeostasis, and the outcome of these interactions on intestinal health and productivity.

Aims The study was aimed to evaluate the antibacterial activity and efficacy of chestnut and quebracho wood extracts against Salmonella by in vitro assays and in vivo trials. Methods and results The extracts showed inhibitory activity against Salmonella determined by the minimum inhibitory concentration method as well as on the adhesion and invasion of S. Gallinarum (SG) and S. Enteritidis (SE) in Caco‐2 cells. Also, transmission electron microscopy revealed that extract‐treated Salmonella showed disruption of cell walls and membranes, damage of the cytoplasm and tannin‐protein aggregations. In addition, efficacy of the extracts to control SG and SE was evaluated in experimental infection trials in laying hens and broilers, respectively. SE excretion was significantly reduced on days five (P<0.01) and twelve (P<0.025) only in the quebracho group. In the fowl typhoid infection model, hens that received the chestnut extract showed a significantly reduced mortality (P<0.05). Conclusions Our results evidence that these alternative natural products may be a useful tool to control Salmonella in poultry. Significance and impact of the study Salmonella is a zoonotic pathogen usually associated with poultry production. This study provides information about the mechanism of antibacterial effects of chestnut and quebracho wood extracts to control Salmonella in poultry.

Background: Beef feedlots are increasing concerns that antibiotic use in beef cattle selects for antibiotic resistance, but limitations of primary studies and previous syntheses make it difficult to confirm a consistent effect. We conducted a rigorous systematic review and meta-analysis to summarise: 1) the effect during and after antibiotic administration; 2) its moderation by time since administration started/ended. Methods: Eligible studies longitudinally compared beef cattle administered antibiotics to those that were not, measuring resistance determinants in faeces and/or environments. Information sources included Web of Science, CAB Abstracts, and Medline (last searches: 05/03/25). Risk of bias was assessed using RoB 2 and ROBINS-I. Meta-analysis was conducted where feasible, using individual participant data where necessary. Results: The 33 included studies were mostly small trials of North American feedlot cattle, all with high risks of bias. Meta-analysis of 11 studies of tylosin, ceftiofur, and chlortetracycline indicated positive effects on absolute abundance of resistance both during (SMDH = 0.4; 95% CI = 0.11 to 0.69, p = <0.01) and after (SMDH = 0.52; 95% CI = 0.33 to 0.71, p = <0.01) antibiotic administration. Log-transformed time was positively associated with effect size during (Slope = 0.63; 95% CI = 0.1 to 1.16, p = 0.02), and negatively associated after (Slope = -0.65; 95% CI = -1.24 to -0.06, p = 0.03) Discussion: Available evidence indicates time-dependent selection for antibiotic resistance in beef cattle, warranting further regulation to limit human health risks. Simultaneously, uncertainty about precise effect sizes warrants further research. Funding: BBSRC Registration: https://doi.org/10.17605/OSF.IO/RXQHT