Antibiotic-free broiler meat production is becoming increasingly popular worldwide due to consumer perception that it is superior to conventional broiler meat. Globally, broiler farming impacts the income generation of low-income households, helping to alleviate poverty and secure food in the countryside and in semi-municipal societies. For decades, antibiotics have been utilized in the poultry industry to prevent and treat diseases and promote growth. This practice contributes to the development of drug-resistant bacteria in livestock, including poultry, and humans through the food chain, posing a global public health threat. Additionally, consumer demand for antibiotic-free broiler meat is increasing. However, there are many challenges that need to be overcome by adopting suitable strategies to produce antibiotic-free broiler meat with regards to food safety and chicken welfare issues. Herein, we focus on the importance and current scenario of antibiotic use, prospects, and challenges in the production of sustainable antibiotic-free broiler meat, emphasizing broiler farming in the context of Bangladesh. Moreover, we also discuss the need for and challenges of antibiotic alternatives and provide a future outlook for antibiotic-free broiler meat production.

Enzymes excreted by rumen microbiome facilitate the conversion of ingested plant materials into major nutrients (e.g., volatile fatty acids (VFA) and microbial proteins) required for animal growth. Diet, animal age, and health affect the structure of the rumen microbial community. Pathogenic organisms in the rumen negatively affect fermentation processes in favor of energy loss and animal deprivation of nutrients in ingested feed. Drawing from the ban on antibiotic use during the last decade, the livestock industry has been focused on increasing rumen microbial nutrient supply to ruminants through the use of natural supplements that are capable of promoting the activity of beneficial rumen microflora. Selenium (Se) is a trace mineral commonly used as a supplement to regulate animal metabolism. However, a clear understanding of its effects on rumen microbial composition and rumen fermentation is not available. This review summarized the available literature for the effects of Se on specific rumen microorganisms along with consequences for rumen fermentation and digestibility. Some positive effects on total VFA, the molar proportion of propionate, acetate to propionate ratio, ruminal NH₃-N, pH, enzymatic activity, ruminal microbiome composition, and digestibility were recorded. Because Se nanoparticles (SeNPs) were more effective than other forms of Se, more studies are needed to compare the effectiveness of synthetic SeNPs and lactic acid bacteria enriched with sodium selenite as a biological source of SeNPs and probiotics. Future studies also need to evaluate the effect of dietary Se on methane emissions.

Aerosol particles and airborne microorganisms are crucial factors of indoor air quality. The purpose of the present study was to evaluate the interrelationships among aerosol numbers, various types of airborne bacteria, temperature, and relative humidity (RH) to decide which parameters have more significant relationships among them. The concentrations of aerosol numbers, airborne total aerobic bacteria, Staphylococcus aureus (S. aureus), and Escherichia coli (E. coli) in the indoor air, as well as indoor and outdoor temperatures and RH, were assessed each week for a total of 20 days in a tie-stall dairy barn during the summer season in Tochigi, Japan. The mean concentrations of the fine aerosol numbers (0.3–2.0 µm) were greater than the mean concentrations of coarse aerosol numbers (5.0–10.0 µm). Among the airborne total aerobic bacteria, the mean concentration of airborne S. aureus was higher compared with airborne E. coli. More significant positive associations were found between outdoor environmental temperatures and aerosol numbers rather than indoor temperatures and aerosol numbers. All three types of airborne bacteria were associated with both outdoor and indoor environmental temperatures. These findings are crucial in the mitigation of aerosol numbers and airborne bacteria in the indoor air of dairy barns.

: The quality of indoor air dramatically affects the health of animals and humans. An investigation was conducted into the relationships among the total number of aerosol particles and different types of airborne bacteria and their dependence on indoor and outdoor environmental factors, including air temperature and relative humidity (RH), in the indoor air of a dairy calf house in Tochigi, Japan, during the summer season. The concentrations of aerosol particles, the concentrations of airborne total aerobic bacteria (, , and spp.) in the indoor air, and the indoor and outdoor temperature and RH were evaluated from 14 weekly measurements. The mean concentration of small aerosol particles (0.3 to 2.0 µm) was higher than the mean concentration of large aerosol particles (2.0 to 10.0 µm) in the summer season. The mean concentration of airborne total aerobic bacteria was higher than the concentrations of airborne , , and spp. Airborne and were positively correlated with the number of 2.0 to 10.0 µm aerosol particles, i.e., high concentrations of 2.0 to 10.0 µm particles were correlated with high concentrations of airborne and . Airborne total aerobic bacteria did not correlate with the number of aerosol particles of any size, but spp. was negatively correlated with the number of 1.0 to 2.0 µm aerosol particles, i.e., high concentrations of 1.0 to 2.0 µm particles were correlated with low concentrations of airborne spp. The indoor temperature and indoor and outdoor RH did not correlate with any airborne bacteria. The outdoor temperature was negatively correlated with spp., i.e., high outdoor temperature was correlated with a low concentration of spp. in the indoor air of the dairy calf house. Both indoor and outdoor temperatures were positively correlated with the number of 0.5 to 5.0 µm aerosol particles, and indoor RH was negatively correlated with the number of 5.0 to 10.0 µm aerosol particles. These findings will be important for elucidating the role of aerosol particles in the transmission of airborne bacteria and ultimately for the mitigation of aerosol particles and airborne bacteria in dairy houses. HighlightsThe number of fine aerosol particles increased with increasing temperatures.Environmental factors had a less critical effect on airborne bacteria than aerosol particles.Airborne E. coli strongly positively correlated with 5.0 to 10.0 µm aerosol particles.Airborne Salmonella spp. negatively correlated with 1.0 to 2.0 µm aerosol particles.Relative humidity did not affect any airborne bacteria. Keywords: Aerosol particle number, Airborne bacteria, Dairy calf, Indoor air, Relationship, Summer season.