Effluent sulphur fate and toxicity Most of the sulphur intake is recovered as sulphate in urine. Mixing of urine and faeces under anaerobic conditions con- duces to a consumption of sulphates in few days with a large production of sulphide. This depletion of sulphate and accu- mulation of sulphides, suggests a dissimilatory sulphate re- duction pathway involved by sulphate reducer micro-organ- isms. The depletion is coupled with an apparent increase of volatile fatty acid consumption, particularly propionate and butyrate, which are required by sulphate reducing bacteria to produce sulphide. The presence of such gas in the barns affects the respiratory tract and animal welfare, as H2 lation, H2


S is extremely toxic. After inha-


S is dissolved in blood and distributed throughout the body (because of its high fat-solubility), interacting with some enzymes. The sulphur can inhibit the cytochrome C oxi- dase activity impacting the mitochondrial respiratory chain and, therefore, oxygen utilisation by the colonocytes. It is also known that H2


S limits butyrate oxidation (responsible for


about 70% of the energy for the colonocytes). This energy deficiency is often associated with the prevalence of ulcera- tive colitis and impaired gut permeability. The deadly atmospheric H2


Figure 2 - Average daily gain of piglets fed different levels of sulphur (S) during 35 days (Iowa: 0.29%, 0.50% and 1.21% S | Illinois: 0%, 0.20% and 0.60% S). 780


Low S


760 740 720 700 680 660


Iowa Illinois S content in the livestock building


is close to 500 ppm but legislation limits worker exposure to less than 10 ppm. That limitation is important to keep work- ers safe, as the literature shows that 33% of accidents are linked to H2


S intoxication provoking worker deaths. In most


cases, the maximum exposure to H2S occurs when the efflu- ent is mixed before land spreading and is well known as “H2


S release rate measured during any period compared to previous ones.


Managing the sulphur produced in farms In pig slurry, H2


S is produced in anaerobic conditions (as pre-


viously mentioned, the sulphate in urine and faeces is re- duced into sulphite and then into sulphide by sulphate-re- ducing bacteria) or as a result of the mineralisation of organic dietary compounds containing sulphur. The feed is ultimately a major source of sulphur in manure, which means that H2


S


production and emission could be reduced by selecting feed- stuffs low in sulphur. The H2


S produced may contribute to odour emissions and


present a risk of intoxication for both farmers and pigs. Be- sides, H2


S is also a highly corrosive gas. That implies that,


when manure is stored to be used for biogas purposes, the H2


S removed, according to the removal S must be removed to reduce engine-generator set main-


tenance costs. Associated costs (including capital, transport and operational expenses) can vary between US$ 3.70 and US$ 6.43 per kg of H2


method. Dry-based chemical methods appear to be the most competitive, with an estimated capital costs around US$ 10,000 – 50,000 per year.


▶ PIG PROGRESS | Volume 37, No. 4, 2021 25 S


burst-release”, which is a sudden increase (100% or greater) of H2


Choice of ingredients The choice of low sulphur feed ingredients can influence the damage caused to intestinal mucosa while reducing the risks of human and pig toxicity in barns. As low sulphur diets generate lower sulphur excretion, a max- imum total dietary sulphur content should be considered to reduce sulphide production during pig manure storage. The right selection of any single ingredients (including sul- phate-free minerals) involved in the feed formulation is a key strategy in sulphur management.


Intermediate S High S


Low sulphur diets generate lower sulphur excretion.


PHOTO: ODAIRSON ANTONELLO | ANIMINE


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