Table 1. Different feed additives for reducing noxious gas emission in pig

Type of additive	Additive	Dose	Animal	Result	References
Probiotics	Bacillus organisms	0.00625% (1.47×108 CFU of Bacillus spp./g)	Growing-finishing pigs	Reduced fecal NH3 emission was found while fecal total mercaptans, H2S and volatile fatty acid was not altered.	[33]
	Lactobacillus plantarum	0.20% (1.30 × 107 CFU/g of L. plantarum /g)	Weaning pigs	Fecal NH3, H2S, total mercaptan, and acetic acid was not changed	[15]
	Probiotics mixture (B. licheniformis, B. subtilis, L. acidophilus and Saccharomyces cerevisiae)	0.20% (5.1 × 107 CFU/g B. licheniformis, 6.3 × 107 CFU/g B. subtilis, 4.3 × 107 CFU/g L. acidophilus and 2.5 × 107 CFU/g S. cerevisiae)	Growing pigs	Fecal NH3, H2S decreased while methyl mercaptans, acetic acid, CO2 was not changed	[35]
	Probiotic complex (L. acidophilus, Saccharomyces cerevisae, and B. subtilis)	0.20% (1.0×107 CFU/g L. acidophilus, 4.3×106 CFU/g Saccharomyces cerevisae and 2.0×106 CFU/g B. subtilis)	Growing pigs	Fecal NH3-N emission decreased while acetic acid, propionic acid and butyric acid was not affected	[80]
	Enterococcus faecium DSM 7134	1.0 × 1010 CFU/g E. faecium	Weanling pigs	Fecal NH3 emission was reduced but H2S was remained unaffected	[34]
	Probiotics complex (B. licheniformis and B. subtilis)	0.2% (3×107 CFU/g of B. licheniformis and 3×107 CFU/g of B. subtilis)	Growing pigs	Fecal NH3 and H2S emission decreased after day 4 of fermentation.	[25]
	B. subtilis and B. licheniformis	0.2% (3.2 × 109 CFU/g of B. subtilis and B. licheniformis)	Growing pigs	Fecal NH3 emission was lowered but while H2S and mercaptan emission was not affected	[81]
	Aspergillus spp., Saccharomyces spp. and Lactobacillus spp.	0.2% (Aspargillus spp., Saccharomyces spp. and Lactobacillus spp.)	Growing pigs	Decreased fecal propionate, ammonia and amine gas emissions, and increased fecal acetate gas emission	[31]
	Bacillus spp.	0.05% (3 × 108 CFU/g Bacillus spp.)	Growing pigs	Methane and ammonia volatilization decreased	[82]
Prebiotics	Fructan	2.0%	Finishing pigs	Fecal ammonia, hydrogen sulfide, total mercaptans decreased	[41]
	S. cerevisiae cell wall extract and poplar propolis ethanol extract	0.10%	Growing pigs	Fecal NH3 and H2S was decreased linearly	[40]
Synbiotics	Probiotics from bacteria or yeast or mold or compounds of bacteria, yeast and mold.	0.2%	Weaning pigs	Ammonia and amine gas emission decreased in bacteria synbiotics, H2S was decreased in bacteria synbiotics, yeast synbiotics, or mold synbiotics	[83]
Enzyme	Enzyme blend (glucoamylase from A. niger, alpha-amylase from B. stearothermophilos, lipase, maltase, cellulose, protease)	1.0%	Grower-finisher pigs	Fecal NH3 decreased while H2S and total mercaptans remained unchanged	[12]
	Protease and fructo-oligosaccharide	0.05% protease and/ or 0.1% fructo-oligosaccharide	Finishing pigs	Total mercaptan and H2S was not changed but fecal ammonia emission decreased in both protease or fructo-oligosaccharide	[59]
	Xylanase	0.01%	Weaning pigs	NH3 and H2S decreased while total mercaptans emission was not altered.	[84]
Medicinal plant	Black pepper (piperine) extract	0.4%	Finishing pigs	Fecal NH3 and methyl mercaptans, and acetic acid decreased linearly. fecal H2S and CO2 was not altered.	[21]
	A. japonica extracts	0.10%	Growing pigs	Fecal H2S emission decreased linearly while fecal NH3 and total mercaptans emission was unaffected	[60]
	Fermented Gynura procumbens, Rehmannia glutinosa and Scutellaria baicalensis	0.2%	Weaning pigs	Fecal NH3 and, total mercaptans and H2S decreased linearly	[85]
	Herb extracts mixture (buckwheat, thyme, curcuma, black pepper and ginger)	0.025%	Growing pigs	Fecal NH3 and H2S emission decreased in the day 2 and day 1 of fermentation respectively	[14]
	Achyranthes japonica Nakai root extract	0.02%	Finishing pigs	Fecal NH3 decreased but fecal H2S and R-SH emissions was not altered	[86]
Organic acid	Mixture of fumaric acid, citric acid, malic acid, and medium chain fatty acid	1.0%	Growing pigs	Fecal H2S emission reduced but ammonia and total mercaptans was unaffected.	[75]
	Fumaric acid, citric acid, malic acid, capric acid, and caprylic acid	0.2%	Growing pigs	NH3 and acetic acid decreased but H2S was not affected	[87]
	Fumaric acid, citric acid, malic acid, capric acid, and caprylic acid	0.2%	Sow	NH3 and H2S decreased but acetic acid was not altered	[76]
	Fumaric acid, citric acid, malic acid, capric acid, and caprylic acid	0.2%	Weaning pigs	NH3 and H2S was not altered	[88]