Figure 2. Sulphur and sulphate trans- formation in the GIT and environment.

cations (Na+ and K+) and one anion (Cl-): dEBmEq/kg = (Na×434.98) + (K×255.74) – (Cl×282.06). Recently, in a feed formulation exercise conducted together with a Dutch research centre, Schotorst, the total S content of a starter corn and SBM-based diet for broilers was increased from 2400 to 3500ppm. Both diets were iso-protein, iso-Met and iso-energetic. SBM inclusion level (22.6%) in the low-S diet was replaced by SBM (11.7%), rapeseed (6.7%), feather meal (3.7%) and hydrolysed porcine intestine (2.04%), all being contributors to S content. The dEB of each diet was calculated using the two available equations. In the first case (using the current dEB equation), both dEB values were very similar (see Table 1), leading to the assumption that this parameter was good and would not affect bird performance. (NB: for optimum performance a dEB of around 240-250meq/kg is required). When the sec- ond equation was applied (Mongin’s calculations with sul- phates), dEB values not only showed a wider divergence from each other but were also below the reference value for performance.

Other toxic S-related compounds In poultry operations emissions of toxic gases, such as hydro- gen sulphide (H2

In poultry production systems, particular attention to H2S toxic-

ity has been given primarily in relation to respiratory disorders. Inhaled H2

S rapidly enters the blood stream, where it dissoci-

ates, binds to haem compounds and is partially metabolized by oxidation to sulphate and excreted in the urine. But excess of H2

S inhibits cytochrome oxidase enzyme which is critical to mi-

tochondrial respiration in the cells. Nervous and cardiac tissues, which have a higher oxygen demand, are especially disturbed by cellular apoptosis and may result in death.

Managing undesirable effects It is highly unlikely that any single feedstuff or additive will cause direct S toxicity in poultry. Nevertheless, the total S supply (in feed and water) should be monitored to avoid S content in excess of 3500ppm, especially if S-rich ingredients are included in the formulation. At such levels, it is important to consider sulphur supply in the dEB equation to ensure that the acidogenic potential of the feed is not neglected. Along- side this wellbeing-related practice, the use of trace minerals from high quality oxide sources, free of S, can contribute to the sulphate content of diets.

S), can influence the prevalence of various dis-

eases. Such emissions also represent an important health risk for workers, particularly during manure-handling processes be- cause of the rapid release of this gas. A study in 2017 reported that H2

S emissions in manure-belt houses are 77% higher than in the old high-rise layer houses. H2S is the final product of sul-

phate-reducing bacteria that anaerobically decompose S-con- taining amino acids and break down sulphates, forming inter- mediate S compounds that ultimately form H2

S (Figure 2). From

human medicine it is known that high concentrations in the gut can adversely affect gut function (increasing inflammation and motility) and microbiota composition.

Table 1 – Simulation of S impact on dEB according to the equation model used.

Current and commonly used DEB equation (Na+

+K+ )-(Cl- +K+ )-(Cl- )

Mongin’s (1981) equation (Na+

189.9 +SO4-) 166.4

Low S diet (2400ppm) High S diet (3500ppm) dEB interpretations DEB in mEq/kg 200

DEB in mEq/kg 207.8

Both diets are very similar and conform to performance level The dEB of both diets differ and are below the reference value

This simulation clearly shows the importance of considering sulphur in the dEB calculation. ▶ POULTRY WORLD | No. 3, 2021 29


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