NUTRITION ▶▶▶
Sulphur and sulphate in diets: is it a concern?
Sulphur-containing compounds are essential elements for pigs. However, a rising concern is about the excess of sulphur sources in the diet, as sulphates could serve as a substrate for increased hydrogen sulphide production by sulphate-reducing bacteria, with effects on gut health as well as effluent composition.
BY ALESSANDRA MONTEIRO AND ARTURO PIÑON, ANIMINE, FRANCE; AND PASCAL PEU, INRAE OPAALE, FRANCE
B
Sulphur-containing proteins
ased on the French feed database, the total sul- phur content of raw feedstuffs can range from less than 0.5g/kg to over 10g/kg. Those different sul- phur values depend on the composition of the
material itself but also on its origin and/or processing. The sulphur content of whole grains (wheat, corn) is relatively low, usually close to 1.3g/kg. However, sulphur content in feedstuffs based on cereals like corn gluten meal can be more than 10g/kg. Dietary sulphur content is directly linked to sulphur amino
Figure 1 - Production of H2 S from two pathways (from sulphur- containing proteins and from SO4–2) in the large intestine of pigs.
acids, sulphate-containing ingredients (e.g. trace minerals) and by-products from the milling industry pre-treated with sulphuric acid to enhance starch extraction. Large variation in the total sulphur content of dietary ingredients might af- fect total sulphur feed intake, sulphur excretion by animals (55% of intake in the urine) and gaseous sulphur emissions from pig slurry during anaerobic storage.
Sulphur and gut health Unlike the extensive understanding of sulphur amino acids metabolism, inorganic sulphur requirements have received little attention. As several feedstuffs and minerals have ele- vated levels of total sulphur, intake can exceed the tolerable limits for pigs and affect gut health. In addition, as absorp- tion of total dietary sulphur is about 65% in pigs, sulphur excretion can have an impact on the soil, water and air. Sulphate-reducing bacteria are able to reduce sulphate to H2
S (see Figure 1).
Those bacteria are present in the gastrointestinal tract (GIT) of animals and can significantly influence the gut environ- ment, due to the production of H2
S and the competition for nutrients. H2S interferes in the colonocytes with metabolic Fermentation Methionine gamma lyase CH3SH CH3SCH3 SO4–2 Reduction Sulphate-reducing bacteria H2S
processes, and it damages the intestinal mucosa. It is con- sidered the third gasotransmitter, after nitric oxide and car- bon monoxide, and is involved in inflammation, gut motili- ty, oxidative stress, ulcer healing, vascular tone and cellular apoptosis. Two experiments conducted at Iowa State University with 13kg pigs fed inorganic sulphur showed a linear reduction in daily gain, and the higher dietary sulphur level did alter inflammatory mediators and intestinal bacteria. A third ex- periment conducted in Quincy, IL, United States involved 9kg pigs, also fed inorganic sulphur, which also showed a linear reduction in daily gain. In both studies the reduction in growth rate was primarily due to an effect of diet on feed intake (see Figure 2). In gilts, graded amounts of sulphur resulted in an increase in manure acidity, nitrogen and sulphur content and odour-related compounds like H2
sulphur salts in monogastric species are usually related to abnormalities in water balance in the GIT, generally mani- fested as diarrhoea resulting from the osmotic attraction of water into the gut lumen.
24 ▶ PIG PROGRESS | Volume 37, No. 4, 2021
S. Toxic effects of inorganic
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