Nitrogen balance, ammonia and odor emissions in growing pigs fed reduced protein diets

The effect of reducing the crude protein (CP) levels in diets fed to growing pigs, was evaluated in two experiments, each using two diets formulated to contain either a normal (19%) or a reduced CP level (14%), with constant levels for standardized ileal digestible lysine (0.85%), and metabolizable energy (3.37 Mcal ME/kg). Exp I measured the N balance of pigs (n= 24) initially weighing 17.7 +/- 1.29 kg, while Exp II used 24 pigs from 17.9 +/- 0.76 kg to assess aerial ammonia (NH3) emissions and odor levels in dynamic airflow chambers for 21 d. In Experiment I, N intake (26.6 %), urinary N (56 %), and total N excretion (41 %) were lower (P<0.001) for the reduced CP level, while fecal N excretion was similar (P>0.4). In Experiment II, reducing dietary CP did not affect (P>0.10) growth performance, but tended to reduce (P<0.10) manure pH (6.71, normal and 6.21 +/- 0.186 for reduced CP) and NH3 emissions, which were diminished after d-9 trial (dietary CP and days in the experiment interacted, P<0.001). Odor levels measured on d-14 and 21 of the study, assessed by olfactometry, did not differ between treatments (512 and 540 +/- 115.6 threshold units for the reduced and normal CP diets), but increased (P<0.01) with time on feed (440 and 612 +/- 111.3 threshold units on d-14 and 21, respectively). These results suggest that each one percentage unit reduction in dietary CP (combined with the appropriate AA supplementation) lowers N excretion (by 8 %) and NH3 emissions from manure (by 15 %), with no effect on manure odor.