Abstract: With the advancement of modern farming, understanding the baseline emissions of gaseous pollutants from pig houses and mitigating them through optimized environmental control and management has become a critical environmental challenge.This study conducted field monitoring in a mechanically ventilated pig barn with a manure scraping system to quantify baseline CO2 and NH3 emissions and to examine how environmental conditions and sow excretory behavior influence emission dynamics. In previous studies, most research compared manure scraper systems with other manure-cleaning methods to explore the advantages and shortcomings of mechanical manure scraper systems in terms of gas emissions, while fewer studies investigated baseline emission levels of barns with scraper system and the effects of excretion behaviors on gases emissions. Based on this, the experiment investigated the influence of excretion behaviour and feeding on the gas emission rate of the pig barn, with a view to providing reference values for the CO₂ and NH₃ emission rates. The field experiment investigated swine excretion behavior on the emission of CO₂ and NH₃ in a swine barn in central China. During the summer of 2023, the experiment took place in a mechanically ventilated pig house with a manure scraping system in Jingzhou, Hubei Province, China. The experimental pig house had a total floor area of approximately 2400 m² and was equipped with 16 units of 50-inches fans and two units of 51-inches fans, all of which were fully operational during the experiment period. By adjusting fan operation, three experimental groups with different ventilation volumes were set up (542, 532, and 536 m³/(h·pig)), and the excretory behaviors of the pigs were recorded to explore baseline gas emissions under this husbandry management approach and to assess the potential influence of ventilation management on emission characteristics. The experimental results showed that: 1)During the experiment, the outside temperature of the house ranged from 30 to 37 ℃, with a relative humidity of 60% to 70%; the inside temperature ranged from 27 to 30 ℃, with a relative humidity of 80% to 95%. Under a ventilation rate of approximately 532～542 m³/(h·pig), the NH₃ concentration was approximately (1.15 ± 0.12) mg/m³; the NH₃ emission rate was approximately (9.28 ± 1.56) g/(d·pig); the CO₂ concentration was approximately (965.88 ± 26.01) mg/m³; and the CO₂ emission rate was approximately (1723.84 ± 327.54) g/(d·pig); Feeding increased both CO₂ and NH₃ emission rates. 2)Pregnant sows exhibited urinary peaks between 12:00 to 15:00 and 18:00 to 21:00 daily, while defecation peaks occurred between 12:00 to 15:00 and 18:00 to 0:00 daily. The average daily frequency of urination per pregnant sow was approximately (3.78 ± 1.56) times, and the defecation frequency was approximately (1.11 ± 0.33) times. These behavioral rhythms were generally consistent with observed temporal variations in NH₃ emissions. 3)There was a significant correlation between NH₃ emission rate and urinary and defecation activities, with correlation coefficients of 0.62 and 0.57, respectively (P < 0.05). However, there was no correlation between CO₂ emission rate and urination or defecation. Feeding increased CO₂ and NH₃ emission rates. Gas emissions from pig houses are influenced by manure removal methods, floor type, temperature, humidity, stocking density, and feeding practices. Adjusting environmental conditions and management practices while ensuring pig comfort may help reduce emissions at the source and provide practical guidance for emission mitigation in modern intensive pig production systems.