Odor components and the effects of different managements on odor characteristics in layer houses

Odor compounds in waste gas emissions have been ever-increasing public complaints to the large-scale intensive farms, particularly with the rapid expansion of the poultry industry in recent years in China. All kinds of waste gases during laying hens breeding have posed a threat to the body health and living environment. It is a high demand to quantify the odor components and their contributions for the higher efficient deodorization of laying hen farms. This study aims to clarify the effects of management measures and manure accumulation on the component and concentration of odors in layer houses. Two typical commercial and breeder layer houses were sampled in summer (2019.07.10-2019.09.24). Four management measures were also set, including no management, feeding, spraying, and manure cleaning, where the frequency of manure cleaning was 2d/time. The results showed that there were similar odor components and concentrations in the two-layer houses, due to the similar feed nutrition. Specifically, the concentrations of odorant compounds in the layer houses were ranked in a descending order of the NH3 (2.26 mg/m3), volatile fatty acids (0.93 mg/m3), volatile sulfur compounds (0.40 mg/m3), phenols (0.36 mg/m3), indoles (0.32 mg/m3), and amines (0.12 mg/m3). The odor contributions were ranked in the descending order of the indoles (72.91%), phenols (10.07%), volatile sulfur compounds (7.85%), volatile fatty acids (4.93%), amines (4.23%), and NH3 (0.01%). Hence, the indole or total volatile organic compound was regarded as the deodorant target in layer houses. In addition, there was no significant difference between the odor concentrations under no management and feeding (P>0.05), indicating that the manure was the main source of odor rather than the smell of feed. The odor concentration under the spraying sanitization was the highest, followed by the manure cleaning. Correspondingly, the NH3 and indole concentrations were attributed to the high concentrations of odor components after the spraying sanitization and manure cleaning. Furthermore, the spraying was expected to significantly increase the relative humidity and the water content of manure, where an excellent environment for the anaerobic fermentation of bacteria and the activity of urease. By contrast, a large number of odorant components were emitted from the end of the manure belt during manure cleaning. The NH3 concentrations increased significantly during the periods of manure accumulation (6 times of initial concentration), but lower than 15 mg/m3 limited by NY/T 388-1999 (Environmental quality standard for the livestock and poultry farm), indicating that NH3 was not the key component to deal with for the deodorization. The concentrations of other components remained relatively stable during manure accumulation, where the total contribution to the odor was 99.99%. Consequently, the components except NH3 came from the degradation of intestinal microorganisms. Anyway, a strong recommendation during this time can be made to scientifically regulate the diet of laying hens using feed additives in the poultry industry.