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Assessing Potential Sulfur Intake Excess in Beef Cattle

This assessment requires estimation of total sulfur concentation (TSC) to determine if there could be a hazard. The maximum tolerated level is 0.4% sulfur as dry matter intake (DMI). It is important to account for all potential sulfur sources from feed and water. TSC is expressed as % sulfur of DMI, and is estimated by adding the sulfur contributed by the water (%SH2O) to sulfur contributed by the feed or forage (%SFF), all on a DM basis.

To use the calculator(Click here):

  • Enter the weight in pounds of the type of cattle under consideration.
  • Indicate lactating or nonlactating.
  • Enter the sulfate concentration of the water source in ppm (same as mg/L). Leave the entry as zero, if the number is unknown.

When the calculation is done, the contribution of sulfur from the water is shown for the water intake levels at different ambient temperature conditions. This contribution is expressed as % sulfur of dry matter intake (DMI).

  • If the total mixed ration has been analysed, enter the identification/name of the ration. In the space "% sulfur in feed" enter the % sulfur as dry matter (DM) measured by laboratory analysis. This is usually expressed as % sulfur, but if the data is given as % sulfate, divide the value by 3. In the space under "Percent of total feed/forage intake" enter the number 100, since this is the total ration.
  • If separate feed/forage components are analysed, enter the names of up to five components in the spaces under feedstuff name. In the spaces under "% sulfur in feed" enter the % sulfur as dry matter (DM) measured by laboratory analysis for each component. These are usually expressed as % sulfur, but if the data are given as % sulfate, divide each value by 3. In the spaces under "Percent of total feed/forage intake" enter the % of the DMI each component is estimated to represent. The sum of these percents must = 100. See the note below on behaviour and feed/forage selection.

After the spaces are filled, click on the calculate button. The information is then summarized as animal information, intake information, and calculated values at several ambient temperature assumptions. The calculated values shown are; 1) estimated water intake in liters, 2) grams of sulfur consumed in water, 3) % S as dry matter contributed by sulfur in water, 4) percent sulfur in all feed or forage, and, finally 5) estimated total sulfur concentration taking all sources into account.

This is the value to be compared to the maximum tolerable sulfur concentration, estimated at 0.4% DM (National Research Council, Nutrient Requirements of Beef Cattle, Seventh Revised Edition, pg 61, 1996). However, the actual risk of polioencephalomalacia depends on the state of ruminal microbial adaptation and other factors in addition to total sulfur intake. (For a more complete discussion of these concepts, refer to Gould, DH: Update on sulfur-associated polioencephalomalacia, Veterinary Clinics of North America: Food Animal Practice, Toxicology. 16:481-496, 2000)

When animals are free to select a particular feed ingredient or forage component, behavior becomes an important variable. Therefore, it is useful to calculate TSC for the animals that might have risky behaviors resulting in an exaggerated consumption of a particular diet ingredient. If the sulfur content of individual dietary components is analyzed separately it is possible to look for specific ingredients that, if selectively consumed by animals manifesting particular eating behaviors, could increase the TSC.

To calculate by hand:

Estimate sulfur contributed by water (%SH2O):

  • Determine the concentration of sulfate in the water by laboratory analysis. Sulfate concentration is usually expressed as parts per million (ppm). Milligrams per liter = ppm.
  • Since sulfate is 1/3 sulfur, mg SO4/L divided by 3 = mg S/L of water.
  • Daily water intake in liters for beef cattle = 8%, 10%, 18% of body weight for ambient temperatures of 40°, 70°, and 90° F respectively. Daily water intake in liters for lactating cows = 10%, 15%, 15% of body weight for ambient temperatures of 40°, 70°, and 90° F respectively. Liters of water intake multiplied by mg S/L = intake of sulfur in mg. Divide by 1000 for intake of sulfur in grams.
  • Daily dry matter intake = 2-3% body weight in kg.
  • %SH2O on DMI basis = total intake of S from water in grams divided by kg DMI divided by 10.

Estimate sulfur provided by feed or forage as % DMI (%SFF):

  • Determine the concentration of sulfur in the total mixed ration or individual diet ingredients. These are usually reported % sulfur as DM. If the data is given as % sulfate, divide the value(s) by 3.
  • If a total mixed ration is analyzed, this is the value to be used as %SFF.
  • If individual feed ingredients or forage components are analyzed, multiply the %S as DM for each ingredient by the proportion of the diet it represents. Then add the proportionally adjusted sulfur concentrations for all the components. This sum is the %SFF.

To calculate the estimated total sulfur concentration:

TSC = %SH2O + %SFF

Sources of Excess Sulfur

  • Water. In many areas of the United States surface and deep waters are high in sulfate. Sulfate salts precipitate where evaporation of high sulfate water occurs. Water sulfate concentrations can increase as water evaporates in hot weather. Water consumption by cattle is temperature dependent. and increases greatly at high temperatures. Therefore, in hot weather, sulfur intake from water can be elevated due to concurrent increases in water consumption and sulfate concentrations in water.
  • Forage. High protein forage such as alfalfa can serve as a source of sulfur, probably as a consequence of the sulfur-containing amino acid content of the protein. It has been shown that rumen microbes incubated ex-vivo can generate H2S from added cysteine and methionine. These sources can make important contributions to the total sulfur intake. In general, grasses tend to be low in sulfur, likely as a consequence of their low protein content. However, under some circumstances grasses can be high in sulfate. Certain weeds seem to be able to accumulate large amounts of sulfate. These include Canada thistle (Cirsium arvense), kochia (Kochia scoparia), and lambsquarter (Chenopodium spp.). These sources can make important contributions to total sulfur intake of ruminants. More needs to be learned about the factors that govern the accumulation of sulfate in plants so that the occurrence of hazardous conditions can be better understood and predicted.

    Cruciferous plants constituitively produce glucosinolates, which have 2 sulfur atoms per molecule. Cruciferous forages serve as important sources of sulfur and have been associated with outbreaks of PEM.

    Co-products of corn, sugar cane, and sugar beet processing commonly have a high sulfur content. This is due to the addition of sulfur-containing a cidifying agents. PEM has been associated with the use of these types of co-products as feed ingredients. A high molasses-urea diet has been associated with a form of PEM. It is likely that this represents a type of sulfur-related PEM due to the high sulfur content of the molasses. Similar scenarios are likely with beet and corn co-products, although careful analyses have not been done.