Gas emission characteristics and influencing factors in a scraper system gestation pig barn during summer

Optimal environmental control is often required to mitigate the baseline emissions of gaseous pollutants from pig houses in modern farming. Previous research has compared mechanical manure scraper systems with manure-cleaning in terms of gas emissions. However, only a few studies have investigated the baseline emission in barns with the scraper system. In this study, field monitoring was conducted in a mechanically ventilated pig barn with a manure scraping system. Baseline CO₂ and NH₃ emissions were then quantified to examine the influence of environmental conditions and excretory behavior on gas emission dynamics. A series of experiments was conducted to investigate the influence of excretion behavior and feeding on the gas emission rate of the pig barn. The field tests were also implemented to determine the effects of the swine excretion behavior on the CO₂ and NH₃ emission rates in a swine barn. A case study was taken of the mechanically ventilated pig house with a manure scraping system in Jingzhou, Hubei Province, China, during the summer of 2023. The pig house with a total floor area of 2400 m² was equipped with 16 units of 50-inches fans and two units of 51-inches fans, all of which were fully run during the experiment period. Fan operation was adjusted to determine three ventilation volumes (542, 532, and 536 m³/(h·pig)). The excretory behaviors of the pigs were recorded to explore baseline gas emissions under this husbandry approach, and then the potential influence of ventilation on gas emissions. The experimental results showed that: 1) The outside temperature of the pig house ranged from 30℃ to 37℃ during the experiment, with a relative humidity of 60% to 70%; The inside temperature ranged from 27℃ to 30℃, with a relative humidity of 80% to 95%. The NH3 concentration and emission rate were (1.15 ± 0.12) mg/m³ and (9.28 ± 1.56) g/(d·pig), respectively, under a ventilation rate of 532-542 m³/(h·pig); The CO₂ concentration and emission rate were (965.88 ± 26.01) mg/m³, and (1 723.84 ± 327.54) g/(d·pig), respectively; Feeding also increased both CO₂ and NH₃ emission rates. 2) Pregnant sows exhibited urinary peaks between 12:00 and 15:00 and 18:00 and 21:00 daily, while defecation peaks occurred between 12:00 and 15:00 and 18:00 to 0:00 daily. The average daily frequencies of urination and defecation per pregnant sow were (3.78 ± 1.56) and (1.11 ± 0.33) times, respectively. These behavioral rhythms were consistent with observed temporal variations in NH3 emissions. 3) There was a significant correlation between NH₃ emission rate and urinary/defecation activities, with the correlation coefficients of 0.62 and 0.57, respectively (P<0.05). There was no correlation between CO₂ emission rate and urination/defecation. Gas emissions from pig houses were influenced by manure removal, floor type, temperature, humidity, stocking density, and feeding practices. Environmental conditions and practices were adjusted to reduce gas emissions at the source. The findings can also provide practical guidance to mitigate the gas emissions in modern intensive pig production.