Study On Emission Characteristics Of Ammonia & Hydrogen Sulfide And Biotoxicity Of Ammonia From Dairy Farms

Ammonia?NH₃?and hydrogen sulfide?H₂S?emitted from dairy farms have a wide range of negative impacts on air environment,human health and animal production.These gases can cause serious damages to respiratory systems and nervous systems of humans and animals after inhalation.In order to mitigate the effect of these harmful gases on animals and humans,current efforts have been focused on nutrition regulation and feeding management.Recently,it has been reported that genomic selection can be adopted to reduce the emission of methane?CH₄?gas and to improve the utilization of nutrients in feed,in order to achieve a long-term and stable emission reduction effect.Similar research on NH₃ and H₂S emission through genomic selection has not been carried out probably due to the lack of basic research.Therefore,this research was carried out to monitor NH₃ and H₂S emission data on dairy farms and study the effect of NH₃ on the respiratory system and nervous system of animals,using a mouse model.It is hoped that this research could provide the basic information of NH₃ and H₂S emission for future mitigating effects through nutrition and animal breeding.This study includes the following three experiments:Experiment 1:to explore the emission characteristics and influencing factors of NH₃ and H₂S in naturally ventilated cow houses.The NH₃ and H₂S concentrations and emission rates were measured in and out of 11 cow barns in 3 typical dairy farms in Henan province in February 2018.NH₃ concentration was determined by sodium reagent spectrophotometry,while H₂S concentration was determined by methylene blue spectrophotometry.The emission rate was estimated by a CO₂ equilibrium method and a hot pressure wind pressure method,while safety protection distance was calculated by the Screen3Model.The concentrations of the gases near the ground were higher than those at the height of 1.5m.There were great differences in gas concentrations in different regions of dairy farms.There were significant positive correlations between the concentration of NH₃ and H₂S and the content of N and S in the feed,as well as the indoor temperature.The average emission rates for NH₃and H₂S were29.33g AU^-1d^-1 and0.254 g AU^-1d^-1,respectively.It was estimated that the comprehensive protection distance of NH₃ and H₂S in the three dairy farms was 400m.The average concentration of NH₃ was much higher than that of H₂S,and the atmospheric protection distance and safety protection distance of NH₃ were both greater than those of H₂S.Experiment 2:the respiratory system is the main target organ for the absorption and action of gaseous toxic substances.The toxicological test of NH₃ was conducted to explore the influence of long-term chronic inhalation of NH₃ on the respiratory system of animals.Ninety SPF ICR young mice?45 male and 45 female?were randomly divided into 3 groups,based on the exposed NH₃ concentrations:0 mg?m^-3,20 mg?m^-3or 200 mg?m^-3.During the test period,the mice were exposed to NH₃ for 4h every day.During the exposure period,no water and food were provided.On day 1,day 7,day 14 and day 28 of the experiment,5?7mice were randomly selected from each group for sampling 1 hour after the exposure.The experimental results showed that NH₃ inhalation led to loss of mucosal epithelial cilia,goblet cell proliferation,4?6 times increase of mucin secretion,destruction of the close connection between mucosal epithelial cells and lung epithelial cells,pulmonary fibrosis symptoms,abnormal increase of TNF-?and other inflammatory factors.At the same time,NH₃inhalation caused the apoptosis of olfactory neurons in the nasal cavity and decreased the thickness of olfactory epithelial cells.Experiment 3:Further pathological analysis and molecular biological analysis of the olfactory bulb,piriform cortex and hippocampus of NH₃-treated mice were performed to investigate the damage to theses tissues caused by NH₃.In addition,the neurobehavioral changes of mice were recorded.Expression of Neu N?a marker for neurons?,PSD95 and SYP?markers for synapses?,and GFAP and IBA-1?markers for astrocytes?was localized and quantified in the olfaction bulb,piriform cortex and hippocampal tissues,while amounts of ammonia and IL-6 in brain tissues and serum of mice were measured.In addition,foraging test,open field test,plus maze test and forced swimming test were performed to the behavior changes after exposure to NH₃.After exposure to NH₃ for 14 days,mice in the two NH₃treatment groups showed significant pathological changes in neurons and synapses,with significant decrease in numbers of neurons,increase of IL-6,and increased numbers of activated astrocytes and microglia.In addition,abnormal behavior was observed,with less activities in foraging,loss of memory,and increased anxiety.This study showed that the major damage to the respiratory system in the early stage of NH₃ inhalation test was first observed at the beginning of the test.Only after 14 days,NH₃exposure caused reduction of numbers of smelling-related neurons and synapses,reduced feeding activity and other behavior changes.These results have provided basis data for reducing emission of harmful gases form dairy farms,formulating reasonable policies for manual management and setting the human health and safety protection threshold.Meanwhile,it could provide some basic data for future animal breeding programs to reduce NH₃ emission and improve utilization of feed nitrogen and sulfur.