Appeasing Pheromones against Bovine Respiratory Complex and Modulation of Immune Transcript Expressions

SIMPLE SUMMARY: Bovine respiratory complex is still a major issue in bovine feedlots. Most of the time, antimicrobial molecules are used to manage these diseases with deleterious consequences for microbiota and the emergence and shedding of resistant bacteria. To improve bovine health and reduce the risk for cattle to develop respiratory infections, alternative molecules such as appeasing pheromones have been developed. In this study, we tested bovine appeasing pheromones in young bulls. We treated them at the beginning of the fattening period and measured zootechnical and health parameters over several weeks. We identified dual effects of pheromone treatment. Indeed, more respiratory clinical signs were observed in bulls who received the pheromone treatment on Day 8 than in bulls who did not, while it was the opposite on Day 30. Regarding the potential mechanism to explain the effect of the pheromone treatment, we identified an increased expression of transcripts associated with the expression of immune molecules involved in the recruitment of cells important to manage pathogens. Our study suggests a positive final effect of appeasing pheromones and opens the doors for future studies in beef cattle. ABSTRACT: Bovine respiratory disease is still a major concern and has major economic impact. Another consequence of respiratory infections is the use of antimicrobial molecules to control bacterial pathogens. This can participate in the emergence and shedding of antimicrobial resistance that can threaten animal as well as human health. Appeasing pheromones with their capacity to reduce stress and thus their ability to preserve the functions of the immune system have been proposed to reduce the use of antimicrobial substances. In this study, we assessed the effect of appeasing pheromone administration on bovine health and performance during the fattening period. Zootechnical and health parameters and whole blood immune transcript expressions were measured over four weeks in bulls to determine the effect of the pheromone. We observed increased clinical signs on Day 8 (D8) and decreased clinical signs on D30 in bulls who received the pheromone and a higher expression of interleukin 8 transcripts in this group than in the control group on D8. Our results are overall in line with previous reports in livestock species. Further studies are needed to shed more light on the effect of appeasing pheromones and decipher their exact mechanisms of action.