Reduced crude protein (CP) diets with synthetic amino acid (AA) supplementation has proven to be an effect way to reduce ammonia (NH3) emissions from swine housing. However, there are very limited comprehensive feed-through-field studies to quantify gas emissions and carbon footprint changes that occur as a result of the feeding strategy. This study investigated air emissions and nutrient balance from swine housing, manure storage, and field applications using a reduced CP diet mitigation strategy.
Seventy-two pigs in 12 experimental rooms (6 pigs/room) were fed standard (18.5% to 12.2% CP over the grow-finish period, 6 rooms) or reduced CP diets (17.5% to 11.0% CP over the grow-finish period, 6 rooms) over the course of 5 feeding phases (107 d, total). The reduced CP diets were formulated to NRC 2012 nutrient recommendations. Diets contained similar energy and lysine contents within each feeding phase. During the animal growth period, animal performance and air emissions were monitored. Results showed that diet did not alter average daily gain (ADG; 1.013 kg/d-pig), average daily feed intake (ADFI; 2.714 kg/d-pig), or feed conversion ratio (FCR; 2.735 kg feed/kg gain). Feeding the reduced CP diet resulted in lower NH3 emissions (33% over the 107-d feeding period). The percent NH3 emission reduction observed for each percentage unit reduction in diet CP content was 47.9%, 53.2%, 26.8%, 26.5% and 51.6% during phases 1 through 5, respectively. No other gases were affected by the dietary treatments.
Manure was collected during the animal growth period and compiled to represent a single sample of manure for each diet treatment across the grow-finish period. Manure was placed in barrels, covered and air flow moved across the barrels for 90 days. During that time, barrels were stirred every hour and air emissions were collected. As a result of feeding the standard CP diet, room NH3 concentration and NH3 emissions were double that observed when the reduced CP diet was offered. No other gases were affected by the dietary treatments.
Post storage, manure was land applied to a soil surface and air emissions monitored. No differences in NH3, nitrous oxide or methane emissions were observed.
These findings illustrate that feeding reduced CP diets that are formulated based on NRC 2012 recommendations provides an effective tool for reducing NH3 emissions from swine housing compared to recent industry formulations. Once manure is moved to long-term storage and applied to fields, diet effects on the volatilization of gases may be different from that observed during housing. Losses during land application were low compared to housing and storage and no diet differences were observed suggesting that land application may not be the best place to target efforts to reduce ammonia emissions. Furthermore, diet strategies that produce large differences in ammonia emissions do not necessarily result in observed differences in nitrous oxide emissions.
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