Odour and ammonia emission from pig manure as affected by dietary crude protein level

The objective of this study was to determine the effects of dietary crude protein (CP) level on odour emission, odour intensity, odour hedonic tone, ammonia and greenhouse gaseous emission from pig manure, and on fresh faeces and manure characteristics. An experiment was conducted with finishing pigs (n = 12) in a randomized complete block arrangement with 2 treatments of 12 and 15% dietary CP in six blocks. The 2 diets were supplemented with essential AA up to the level of the animal's requirement. Pigs with an initial body weight (BW) of 57.7 ± 0.7 kg were penned individually in partly slatted floor pens. Faeces and urine of each pig accumulated in separate manure pits under the slatted floor. In the 3rd week of the collection period, fresh faeces were collected for identifying fresh faeces characteristics and for assessing dry matter, organic matter, nitrogen (N), fat and non-starch polysaccharides digestibility using Cr2O3 as a marker. In the 6th week of the collection period, air samples were collected directly from each manure pit: one for odour, one for ammonia concentration and one for greenhouse gases. Afterwards the manure was mixed and a representative sample was taken for manure characteristic analysis. Odour samples were analyzed for odour concentration and for hedonic tone and odour intensity. Manure samples were analyzed for volatile fatty acids (VFA), indolic, phenolic, sulphurous compounds, ammonium and total N concentrations and pH. Reducing dietary CP level from 15 to 12% did not affect odour emission, odour intensity and odour hedonic tone and greenhouse gaseous concentration (CH4, CO2 and N2O) (P > 0.05) of odorous air above the manure pit. Reduced dietary CP level decreased manure pH (P <0.001), total N (P <0.001) and ammonium (P <0.001) concentrations and ammonia emission from pig manure (P = 0.03). In addition, total VFA, acetic, propionic, iso-butanoic and iso-pentanoic acids, phenol, 4-ethyl phenol and carbon disulfide concentrations in manure were decreased by reducing dietary CP level (P <0.05). We conclude that reducing dietary CP from 15 to 12% did not reduce odour emission and greenhouse gaseous concentration; however, ammonia emission was significantly reduced.