The influence of diet crude protein level on odour and ammonia emissions from finishing pig houses

Feed trials were carried out to assess the influence of crude protein content in finishing pig diets on odour and ammonia emissions. Eight pigs (4 boars and 4 gilts), average initial weight 70.8 kg (s.e. 3.167) were housed in two pens that were isolated from the rest of a pig house at University College Dublin Research Farm, Newcastle, Dublin, Ireland. Four diets containing 130, 160, 190 and 220 g kg−1 crude protein were fed during six four-week feeding periods (one treatment per room). The first week of the feeding periods served to allow odour build up in the pens and as a dietary adjustment period. The pens had partially slatted floors that were cleaned and had all the manure removed after each four-week period. Odour and ammonia concentrations were measured on days 9, 14, 16, 21 and 23 of each trial period. Odour samples were collected in Nalophan bags and analysed for odour concentration using an ECOMA Yes/No olfactometer. The odour threshold concentration was calculated according to the response of the olfactometry panel members and was displayed in OuE m−3, which referred to the physiological response from the panel equivalent to that elicited by 40 ppb v−1n-butanol evaporated in 1 m3 of neutral gas. Ammonia concentrations in the ventilation air were measured using Dräger tubes. The odour emission rates per animal for the 130, 160, 190 and 220 g kg−1 crude protein diets were 12.1, 13.2, 19.6 and 17.6 OuE s−1 animal−1, respectively (P<0.01). The odour emission rate per livestock unit (500 kg) for the 130, 160, 190 and 220 g kg−1 crude protein diets were 77.6, 80.0, 115.8 and 102.9 OuE s−1 LU−1, respectively (P<0.01). The ammonia emission rates per animal for the 130, 160, 190 and 220 g kg−1 crude protein diets were 3.11, 3.89, 5.89 and 8.27 g d−1 animal−1, respectively (P⩽0.001). There was no significant difference in the average daily intake and the average daily gain for the four diets (P>0.05). Manipulation of dietary crude protein levels would appear to offer a low cost alternative, in relation to end-of-pipe treatments, for the abatement of odour and ammonia emissions from finishing pig houses