Ammonia emission modelling and reduced sampling strategies in cage-based laying hen facilities

Ammonia (NH3) is the major source of N loss related to laying hen facilities. Previous studies are often based on continuous monitoring of NH3 concentration and ventilation rate in the facilities during long periods. The objectives of this study were (i) to relate climate and production management parameters to model NH3 emission, (ii) to check the accuracy of the proposed model and (iii) to evaluate the accuracy of reduced sampling strategies in estimating NH3 emission. Four datasets of laying hen facilities located in areas representing different climates in Spain were used for model development and reduced sampling strategies evaluation. Indoor and outdoor temperatures, relative moisture, ventilation rate, NH3 concentration, hen live weight and feed N consumption were introduced in the statistical analysis. Outdoor temperature was the main factor related to NH3 emission. Tests showed that the variation between the model estimates and on-farm calculated NH3 losses was, on average, ±15%. Four sampling frequencies were tested to evaluate reduced sampling strategies. The reduction of the sampling frequency resulted in an increase of estimation error ranging from <±10% for weekly to ±20% for bi-monthly sampling. It was concluded that (i) NH3 emission estimation by using simple explanatory variables like outdoor temperature, and (ii) applying sampling reduction strategies can be feasible means to reduce the effort and labour demand of continuous monitoring by obtaining NH3 emission estimates with an assumable associated error