The Characteristics of Key Odorants from Livestock Farms and Their Mitigation Potential: A Meta-Analysis

The persistent issue of odor nuisance poses significant challenges to the sustainable development of livestock farming. While previous studies have primarily focused on individual gas concentrations, a comprehensive understanding of overall odor impact based on human perception remains limited. This study introduces a novel perspective by employing the odor activity value (OAV)—calculated from the ratio of gas concentration to its olfactory threshold—to evaluate the actual odor contribution of various compounds. Through a meta-analysis of data from 123 papers, we systematically assessed odor emission characteristics and mitigation strategies across different manure management stages. The results indicated that ammonia (NH3) (with maximum concentration of 8056 ppm) and hydrogen sulfide (H2S) (with maximum concentration of 20,057 ppm) were the most concentrated odor components in the whole manure management links. However, considering the olfactory threshold, trimethylamine (TMA) (with OAVmax 380800), H2S (with OAVmax 48919512), butyric acid (with OAVmax 801684), and aldehydes (with OAVmax 11707) played major odor-causing roles. Notably, biological methods (83%), covering (77%), and additives (39%) were the most efficient odor mitigation strategies in the barn, manure storage, and manure treatment link, respectively. Therefore, employing the OAV-based approach is crucial for identifying priority pollutants and developing targeted control strategies across different livestock species and management stages, ultimately guiding more effective odor mitigation and healthier cohabitation.