Respiratory disorders in farms are among the main reasons that justify the use of antibiotics. The molecules used in this context are said to be "critical" because they are last generation molecules. Respiratory disorders are among those that generate the highest number of decreasing growth performance. They result in high morbidity and also in particularly high mortality rates. Livestock buildings have modernized to adjust the changes in environmental conditions (temperature, humidity, gas emissions...). However, for a better management of these risks, it is important to act at the upstream stage of the rearing cycle, by supporting the animal’s natural defense barriers and by sustaining, as early as possible, the animal’s respiratory stress phases.