Looking at sulphur and sulphate levels in poultry diets

In its organic form sulphur is an essential element for poultry as it is involved in protein synthesis. However, as with most elements, with elevated intakes from both feed and water there is a potential for toxicity.


100 120


20 40 60


0,37% Ca Trial 1992 (7-21 d) Sulfur content (ppm)

1,32% Ca 28 ▶ POULTRY WORLD | No. 3, 2021 0,36% Ca Trial 1994 (1-21 d)

uring the early years of dedicated poultry produc- tion, feed was based on single cereal and protein source ingredients. Although rarely measured at that time, sulphur (S) content in corn could range

from 300 to 4,000ppm. Indeed, S is one of the essential ele- ments for plant development and is required by the corn. Later, with the intensification of crop harvest yields and more rational application of manure to soils, an increase in S defi- ciency in corn crops was observed. This led to the application of fertilizers to enhance S content in corn. Over the last dec- ade, a significant increase in dietary sulphur content contin- ued to occur in livestock diets with the use of DDGS (essen- tially, concentrated corn) as a cost-effective ingredient, and the use of trace minerals in the form of sulphate.

Figure 1 - Relative weigth gain (% to control treatment) of broilers fed S-supplemented SBM diets.

1400 2800

2700 4200

4000 5600


Nowadays, most macro and micro ingredients used in poultry diets contain some S, either as organic compounds (methio- nine and cysteine), sulphates (trace mineral sources, lysine and sulphamethazine) or toxic glucosinolates (present in for- mer canola varieties). Organic S compounds in the form of amino acids or vitamins (thiamine and biotin) are essential nutrients for poultry. Like other vertebrates, birds are not ca- pable of synthesizing these nutrients from inorganic S so they must be supplied by the diet. But according to the NRC recomendations (2005), maximum tolerable levels of S in the diet in poultry are 4,000ppm.

Understanding sulphur toxicity Sulphur toxicity in poultry is known to induce nonspecific pathological conditions, such as poor growth performance, impaired ash deposition in bones, disturbed ovary function and wet litter issues. The interest in S toxicity came along with the use of sulphamethazine for the control of coccidio- sis. Although very effective, the product was seen to be detri- mental in overdosing situations that often occurred when ap- plied in drinking water. Harmful effects attributed to S have been reported at in- gestion levels above 3,000ppm. The University of Guelph (Canada) has conducted trials to assess the growth of broilers in response to S intake. With increasing inorganic S content, a linear depression in weight gain was reported as a con- sequence of reduced feed intake and due to an impaired anion-cation balance (Figure 1).

Impact of S on dEB calculation In 1981 Pierre Mongin from INRA (France) showed the impor- tance of maintaining a constant electrolyte balance in the diet (dEB). Mongin’s original equation included the sulphate pres- ent in the diet: DEBmEq/kg = (Na×434.98) + (K×255.74) – (Cl×282.06) – (SO4×208.29). Over time, the sulphate component in the equation was ig- nored as it was deemed less metabolically active than Cl- and because dietary SO4- levels were considered to be low. The current equation for calculating dEB only considers two

Relative weight gain (%)

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