With growing environmental concerns and the emphasis on sustainable development in pig production, the emissions of ammonia (NH3) and greenhouse gases (GHGs) have emerged as a progressively significant issue within the industry. Optimizing the manure removal systems could modify the physicochemical properties of manure in pig houses, which results in the reduction of these gas emissions. The objectives of the study were to assess the gas emission reduction strategies of two classic manure removal systems, scraper and pull-plug system, in a scale-down pig house model. Three manure removal systems were designed: scraper-Ⅰ (1 time per day, scrapping manure at 8:00), scraper-Ⅱ (2 times per day, scrapping manure at 8:00 and 16:00) and pull-plug system (retaining manure for 44 days). NH3, CH4, CO2, and N2O concentrations were measured continuously with a trace gas analyzer during the experimental period. Slurries in each group were randomly collected after manure removal and the characteristics (pH, EC, dry matter, total nitrogen, total ammonium nitrogen and total carbon) were analyzed. The results showed two scraper systems had relatively lower GHGs, expressed as CO2-equivalents, and NH3 emissions than the pull-plug system in general, and scraper-Ⅰ showed lower GHGs emissions and higher NH3 emissions than scraper-Ⅱ. The average NH3 emission rate of scraper-Ⅱ was the lowest, 32% and 38% lower than that of scraper-Ⅰ and pull-plug system, respectively. The average emissions of other gases (CH4, CO2, and N2O) in scraper-Ⅰ were 54%, 56% and 25% lower than those in scraper-Ⅱ, and 71%, 67% and 6% lower than those in pull-plug system. A greater increase in GHGs emissions, expressed as CO2-equivalents, was observed in pull-plug system than scraper-Ⅰ (2.1 times) and scraper-Ⅱ (1.6 times). Moreover, diurnal variation of NH3 emission rates was observed in three systems, which showed a temporary peak after each application of urine. Also, the extreme values of NH3 emission rates were observed during each manure removal. In pull-plug system, a burst of growth of each gas emission was observed during the period from Day 39 to Day 41. The total nitrogen and total ammonium nitrogen of slurry for the scraper system were lower than the pull-plug system, while the total carbon was higher. The results of this study build the foundation of gas emission estimation and GHGs emission inventory estimation, reduction strategy, which can guide the manure removal system design and daily operations in pig farms
