Impact of Sulfur Level and Source on Manure and Air Emissions from Swine Diets

Sulfur is a key nutrient associated of H₂S emission and associated with both odor emissions and respiratory distress of animals. Due to potential increases in S levels in swine diets, two experiments were conducted to determine the effect of dietary S level and source on manure slurries chemical properties and gas emissions. Experiment 1 investigated the effects of increasing dietary S level while Exp. 2 evaluated the source of increased dietary S. In Exp. 1, 24 gilts averaging 152 kg BW were fed four different diets ranging between 1,800 and 6,000 mg/kg total S, as supplied by CaSO₄, with an ADFI of 3.034 kg/d over the 31 d trial. In Exp. 2, 24 gilts averaging 139 kg BW were fed a diet containing either 1,800 mg/kg total S or diets containing 3,500 mg S/kg diet as supplied by CaSO₄, distillers dried grains with solubles (DDGS), or feather meal (FM) with an ADFI of 2.705 kg/d over the 41 d trial. In each experiment, feces and urine were collected after each feeding and added to manure storage containers. At the end of each experiment, manure slurries were monitored for gas emissions and chemical properties. In Exp. 1, regression analysis was used to determine the effects of S in the diet. Sulfur lowered manure pH by 1.36 units, but increased S and sulfide levels in manure by 57% and 0.8%, respectively, for each g of S added to the diet. Sulfur increased emissions of H₂S by 8% and odor by 2% for each g of S increase in the diet. In Exp. 2, ANOVA indicated that S source had a significant effect on excretion of DM, C, N, S in manure. Animals fed FM and DDGS diets had significantly higher levels of VFAs, phenols, and sulfide in manure compared to animals fed CSBM diets. The S levels in the diets significantly increased odor emissions compared to CSBM diets. Animals fed FM and DDGS had a greater percentage of chemical odor associated with VOCs than CSBM diets, and animals fed FM diets had significantly higher levels of odor emissions. In conclusion, dietary S levels and the source of S have a dramatic impact on manure composition and gas emissions.