A few months ago the FEEDAP Panel evaluated the safety and effectiveness of sodium-molybdenate as a trace element compound. The application had originally been made for all animal species and categories, but in the course of consultations in the responsible working group it was reduced to sheep. Sulfur is one of the principal actors that determine the safety (compatibility limits) and toxicity of molybdenum and of copper (mainly together with molybdenum) via a large number of interactions. S-surpluses lead to the known interactions between S with Cu and Mo, as well as of S with vitamins (for example retinol, thiamine, biotin). They also have negative effects on the absorption of different trace elements (for example Cu, Se, Zn). That is why the authors thought it a good idea to cast a separate glance at the sulfur supply of the productive livestock.

In the past years not much attention has been paid to the sulfur concentration in the feed, apart perhaps from the S input via amino acids containing S (methionine, methionine hydroxy analog, cysteine) and various vitamin-like substances (for example alpha lipoic acid, methylmethionine sulfonium chloride (Vitamin U) or taurine). It was largely left out of consideration that S-fertilising (for example of oilseed rape), the processing of vegetable raw materials as well as the amount of by-products used as feed have increased further. Today, considerable amounts of sulfur can make their way into the feed rations through a variety of feedstuffs (for example by-products of oilseed rape, by-products of microbial processes; by-products of sugar beet, dried distiller’s grain), mineral feedstuffs (Ca, Mg, Na) in sulfate form and individual feed additives (for example lysine-sulfate, trace elements in sulfate form). The S-content in cereal grains, grasses (including maize), legumes and cereal straw is <2 g="" kg="" dm="" of="" which="" about="" 50="" is="" accounted="" for="" by="" amino="" acids="" depending="" on="" the="" stage="" vegetation="" and="" location="" distinctly="" higher="" s-concentrations="" up="" to="" 8="" s="" are="" possible="" in="" various="" grasses="" legumes="" most="" cereal="" by-products="" reach="">5 g S, in some cases even >10 g S/kg DM.

Relatively recent original studies and overviews from the German-speaking area (for example Dänicke and Schenkel 2009; Züchtungskunde 81; 442-450; Kamphues et al. 2014; Übersichten zur Tierernährung 42; 81-139) and the international language area (for example Kerr et al. 2011; J. Animal Sci. 89; 426-437; Kim et al. 2014; J. Animal Sci. 92; 4486-4493) provide information about the consequences of higher sulfur levels in the feed on animal health and performance levels.

Neither ruminants nor non-ruminants are very tolerant of high sulfur uptakes. Various compounds containing sulfur are reduced down to H2S in the rumen and then partially installed in microbial protein by the rumen flora. After absorption of the compounds with an S-content, these are quickly oxidised to sulfate in the liver and then eliminated with the urea. A reduction of the feed intake and the growth rate in cattle and sheep has already been observed at 3-4 g S/kg DM, for which the H2S formation in the rumen is considered to be mainly responsible.

This compound can also be absorbed and contribute to disorders of the central nervous system and brain lesions, that are termed polioencephalomalacia or cerebro-cortical necrosis (CCN). This can at least partially explain and help to avoid the diseases observed among fattening lambs and beef cattle fed with rations rich in feed concentrate and poor in structurised feed.

Several disorders observed among ruminants are also described for non-ruminants. High sulfur intake can also lead to a reduction of the dry matter content in the excrement and increasingly to diarrhoea. For example increasing the share of sugar beet vinasse from 16 to 43% of the DM uptake of fattening pigs (increase to 21 g S/kg DM) can lead to a reduction of the dry substance content in the dung from 35 to 5% and accordingly to acute diarrhoea.

Already in 2005 the National Research Council (NRC) in the USA devoted a substantial amount of attention to sulfur in its thematic magazine "Minerals in animal and human nutrition" and formulated maximum content levels (for example <3 g="" s="" kg="" dm="" in="" rations="" rich="" feed="" concentrate="" and="" 5="" staple="" for="" ruminants="" 4="" non-ruminants="" that="" should="" if="" possible="" not="" be="" exceeded="" br="">
The S/SO4-content in the drinking water should also be mentioned. In Germany, no more than 500 mg SO4 (or 150-200 mg S) should be contained per litre of drinking water for both ruminants and non-ruminants. Accordingly, at a mean water intake of about 2 to 3 l/kg DM around 0.5 g S/kg DM can be taken in via the water alone. According to the NRC (2005), the maximum S-limits in the drinking water are 200 or 800 mg/l when feeding rations rich in feed concentrate or rations rich in roughage to ruminants, and 1000 mg/l for pigs. Poultry appear to be particularly sensitive – the maximum limit here is only 330 mg S/l.

Taking these current findings into account, it should be considered whether or not binding maximum content levels should be formulated for the total sulfur content in complete feed. It would be desirable to include maximum sulfur levels in existing quality standards as a self-obligation of the industry. Including sulfur in the list of undesirable substances is only an ultimo ratio if other measures do not produce results or are not available.
The Authors
The authors – Gerhard Flachowsky and Jürgen Gropp – are long-serving members of the EFSA Panel on Additives and Products or Substances in Animal Feed (FFEDAP). They report on the work of the FEEDAP Panel. The articles contain personal views and representations, not those of EFSA or the EU. Consequently they do not necessarily coincide with the viewpoints of EFSA or the EU. Consequently they do not necessarily coincide with the viewpoints of EFSA or the EU. As experts working on behalf of EFSA, the authors are subject to certain confidentiality obligations.