Mitigating Ammonia Emissions from Liquid-Sprayed Litter of Cage-Free Hen House with a Solid Litter Additive

Abstract. A number of restaurant chains, retailers, and grocers in the US have pledged to source cage-free (CF) eggs only in the foreseeable future (e.g., by 2025 or 2030) due to marketing reasons or concerns over animal welfare. However, CF housing has some inherent challenges and a predominant one is poor air quality (ammonia gas – NH₃ and particulate matter – PM) and increased emissions. The high NH₃ levels primarily arise from the extended accumulation of manure on the litter floor, whereas the high PM levels are generated from dustbathing and foraging activities of the birds on the litter. Spraying liquid agent such as electrolyzed water (EW) has been shown to effectively suppress PM from litter of CF hen houses. However, liquid spray could enhance NH₃ emissions as it increases the litter moisture content (LMC). Application of low pH liquid to the litter would help control NH₃ while suppressing PM, but concerns arise about the potential corrosive effect of acidic liquid on the housing equipment. To overcome this dilemma, this study evaluated the effect of applying a commercial poultry litter additive (LA, PLT^®) on NH₃ emissions of CF hen litter sprayed with neutral EW (NEW) at dosage of 25 mL (kg dry litter)^-1 d^-1. The PLT application rates were 0.3, 0.6, and 0.9 kg m^-2, denoted as Low-LA, Med-LA, and High-LA, respectively. The litter samples were placed inside dynamic emission chambers (DECs) and stirred to mimic hen scratching. PLT was topically applied onto the litter on day 1; NEW was sprayed daily for 11d, followed by a 3-d non-spray period (i.e., 14 d per trial); and each regiment was replicated four times. Ammonia emission rate (ER) of the control-no LA, Low-LA, Med-LA, and High-LA regimens (mean±SE) was 0.76±0.05, 0.55±0.06, 0.37±0.04, and 0.16 ±0.02 g (kg dry litter)^-1d^-1, respectively, namely 28-79% reduction by the treatments. The NH₃ reduction efficiency is linearly proportional to the PLT^® application rate, with higher application rate resulting in significantly lower litter pH (P<0.05). On the last day of each trial (d14), the Med-LA and High-LA regimens continued to show relatively low NH₃ emissions, suggesting the need for a longer measurement period in the field verification that will follow. The NEW spray increased LMC by up to 60% after 11 once-a-day sprays, which reduced PM_2.5, PM₁₀, and TSP levels from 3.83, 6.39, and 7 mg m^-3 to 0.07, 0.14, and 0.15 mg m^-3, respectively. After a 3-day spray suspension, the PM levels rebounded to 0.72, 1.02, and 1.12 mg m^-3 for PM_2.5, PM₁₀, and TSP due to decreased litter moisture. The trade-off between NH₃ emission reduction and the cost associated with the litter additive application needs to be assessed under commercial CF production conditions.