Effects of Different Laying Hen Species on Odour Emissions

Simple Summary Odour emissions from the laying hen industry receive considerable attention because they influence the air quality, the efficiency of animal production and the health of workers. Recently, numerous researchers have hypothesized that the choice of animals may influence the emission of gases, which may be utilized as the basis for gas pollution reduction strategies in the future. The present study employed an in vitro fermentation technique to simulate gas production from the caecum to explore the effects of laying hen species on the production of ammonia (NH3) and hydrogen sulphide (H2S). The results showed that the Xinghua laying hen had the lowest odour gas production among the six laying hen species tested. Spearman correlation analysis showed that odour production was associated with enzyme activities but was not significantly associated with specific enzyme genes. The results of this study provide useful information for odour reduction in the laying hen industry. Abstract Odour is one of the main environmental concerns in the laying hen industry and may also influence animal health and production performance. Previous studies showed that odours from the laying hen body are primarily produced from the microbial fermentation (breakdown) of organic materials in the caecum, and different laying hen species may have different odour production potentials. This study was conducted to evaluate the emissions of two primary odorous gases, ammonia (NH3) and hydrogen sulphide (H2S), from six different laying hen species (Hyline, Lohmann, Nongda, Jingfen, Xinghua and Zhusi). An in vitro fermentation technique was adopted in this study, which has been reported to be an appropriate method for simulating gas production from the microbial fermentation of organic materials in the caecum. The results of this study show that Jingfen produced the greatest volume of gas after 12 h of fermentation (p < 0.05). Hyline had the highest, while Lohmann had the lowest, total NH3 emissions (p < 0.05). The total H2S emissions of Zhusi and Hyline were higher than those of Lohmann, Jingfen and Xinghua (p < 0.05), while Xinghua exhibited the lowest total H2S emissions (p < 0.05). Of the six laying hen species, Xinghua was identified as the best species because it produced the lowest total amount of NH3 + H2S (39.94 µg). The results for the biochemical indicators showed that the concentration of volatile fatty acids (VFAs) from Zhusi was higher than that for the other five species, while the pH in Zhusi was lower (p < 0.01), and the concentrations of ammonium nitrogen (NH4+), uric acid and urea in Xinghua were lower than those in the other species (p < 0.01). Hyline had the highest change in SO42− concentration during the fermentation processes (p < 0.05). In addition, the results of the correlation analysis suggested that NH3 emission is positively related to urease activities but is not significantly related to the ureC gene number. Furthermore, H2S emission was observed to be significantly related to the reduction of SO42− but showed no connection with the aprA gene number. Overall, our findings provide a reference for future feeding programmes attempting to reduce odour pollution in the laying hen industry.