Content of dietary fermentable protein and odour from pig manure

An experiment was conducted in growing pigs to determine the effects of content of potentially fermentable protein (FP) on odour and ammonia emissions from pig manure and on manure characteristics. Pigs (n =18) were allocated in a randomised complete block arrangement with 3 treatments in each of 6 blocks. The three treatments had 28.4, 38.2 and 48.0g fermentable protein per kg of feed. Pigs with an initial body weight (BW) of 41.3±3.2kg (mean±S.D.) were housed individually in pens with partly slatted floor and offered a daily feed allowance of 2.8xmaintenance requirement (293kJ net energy (NE)/BW⁰.⁷⁵). Feed was mixed with water (1/2.5; w/w). After a 2-week adaptation period faeces and urine produced by each pig were collected in individual manure pits under the slatted floor. In the 5th week of the collection period air samples were collected from each manure pit for odour and ammonia analyses. Odour characteristics were measured by olfactometry and ammonia was measured by using two ammonia traps each containing 20ml 0.5M HNO₃ solution. Manure samples from each manure pit, taken in the same week as air samples, were analysed for volatile fatty acids (VFAs), indolic, phenolic, sulphurous compounds, ammonium nitrogen and total nitrogen concentrations. Data were evaluated using analysis of variance. Odour and ammonia emissions from pig manure were in the range from 1.88 to 2.78ouE/(sm²) and from 0.011 to 0.014mg/(sm²), respectively and were not affected by fermentable protein content of the diet (P>0.05). Increased fermentable protein content resulted in higher concentrations of total nitrogen, methyl sulphide, carbon disulphide, ethanethiol, phenol, 3-methyl indole and 4-ethyl phenol in the manure (P<0.01), but did not influence ammonium nitrogen, volatile fatty acids, cresols and indole concentrations in the manure. It is concluded that a decrease in the fermentable protein content of the diet does not reduce odour emission, odour intensity (OI) or odour hedonic tone (HT) in pigs.