Ammonia emissions of pullets and laying hens as affected by stocking density and manure accumulation time

Data on ammonia (NH3) emissions from pullets (hens <18 weeks of age) are non-existent despite the large differences in nutritional and environmental conditions between raising pullets and laying hens. Different stocking densities (SDs) in housing the birds may be used according to certain industry guidelines on production; however, information concerning the impact of SD on properties of accumulated manure and thus NH3 emissions is limited in the literature. It was hypothesized that bird SD affects the amount of manure per unit of storage or surface area as manure accumulates, and the exposed manure surface area may in turn affect NH3 emission from the accumulated manure. A lab-scale study was conducted that resembled the conditions of manure-belt laying-hen houses with the objectives of (1) determining the magnitude of NH3 emission rate (ER) of pullets (W-36 breed) as a function of age, and (2) assessing the effect of SD on NH3 ER of pullets and laying hens during a 6-day manure accumulation time (MAT). Two SDs at a given bird age (4 to 37 weeks) were evaluated, ranging from 155 and 206 cm2 to 413 and 620 cm2 (24 and 32 in.2 to 64 and 90 in.2) per bird, designated as high density (HD) and low density (LD), respectively. Ammonia ER was expressed on the basis of per bird, per animal unit (AU, 500 kg live body weight), per kg of feed nitrogen (N) use, and per kg of as-is or dry manure. Results showed that daily NH3 ER for pullets and laying hens increased exponentially with bird age and MAT (p < 0.0001). Compared to the HD regimen, the LD regimen had 51% lower NH3 ER (in mg bird-1 d-1) for 4- to 5-week-old pullets and averaged 22% lower for laying hens. Results of this study provide a scientific basis concerning the impact of certain management practices on NH3 emissions and offer insight into reducing NH3 emissions from egg production operations.