Group feeding pig trials were conducted to determine the effects of a specific fiber addition (soybean hulls) and nitrogen manipulation in pig diets on production of odorous ammonia, sulfides, phenols, volatile fatty acids and other volatile organic compounds (VOC) from swine production facilities. Standard commercial diet (control) versus a low crude protein diet (reduced 4.5% CP) supplemented with synthetic amino acids (AA) (Trial 1), low CP diet supplemented with AA versus low CP+AA with 10% soy hulls (SH) (Trial 2) and control versus a control with 10% SH (Trial 2) were compared in replicated studies in two environmentally controlled rooms. Pig performance, carcass quality, manure composition and room air quality data were collected and statistically analyzed.
Based on these group feeding field-type studies, an approach of reducing CP and supplementing diets with synthetic amino acids can be an effective way to control ammonia and odor emissions from confinement buildings. There were 40% reductions in aerial and pit ammonia concentrations with pigs fed the RCP diet. Along with this, there was a 40% lowering of aerial hydrogen sulfide concentrations, and the odor dilution ratio decreased by 30% when pigs were fed the RCP diet. In this experiment, these reductions in odor and gases came at the expense of growth and carcass characteristics. A reduction in CP of 4.5% may be too much, but reducing the CP in diets by 3 to 3.5% could be a good compromise to still reduce odorous emissions and nutrient excretion while maintaining comparable growth and feed efficiency.
Reducing the dietary CP and adding 10% soybean hulls to diets will lower aerial ammonia content (40%), pit total nitrogen, pit ammonia (29%), pit pH, and possibly aerial hydrogen sulfide levels. The addition of fiber to low CP diets did not increase 2 odor control benefits in this study compared to the first study. With the variability in performance, the optimum level of soybean hull addition to a reduced crude protein diet for efficient production and effective odor remediation needs to be tested further.
However, the addition of 10% soy hulls and 4.4% fat to standard corn-soybean diets can have a positive impact towards environmental stewardship, without hindering growth performance and carcass characteristics. The addition of soy hulls lowers aerial ammonia concentration (20%) and hydrogen sulfide levels (32%) in room and exhaust air. There is also an increase in the manure N content indicating greater retention of N in the manure and less volatilization. This increased manure N should also be in a more stable microbial protein form and provide a reduced environmental runoff potential.
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