Sulphur and Sorghum Grazing: What Cattle Producers Need to Know

More sulphur isn’t necessarily better sulphur. 

Sulphur has a requirement and a ceiling. When cattle are grazing forage sorghum, the goal is not simply to add sulphur. It is to understand what the animal is already getting from the forage and drinking water, identify the gap, and supplement it appropriately. 

That matters because sulphur supplementation is only one part of managing cattle on sorghum. 

Why sulphur matters when grazing sorghum 

Some sorghum plants can contain cyanogenic compounds that release hydrogen cyanide (HCN) when consumed. 

The level of risk can vary with the sorghum variety, plant growth stage, crop condition and cattle behaviour. Stress factors such as drought, frost, wilting or crop damage also need to be considered. 

This means there is no single sulphur rate that can be applied to every sorghum paddock. 

Sulphur supplementation is one part of the nutritional program. Forage testing, crop management and cattle management remain essential. 

Start with the total diet, not the supplement 

The animal does not consume supplement sulphur separately from everything else in the diet. 

Total sulphur intake can come from: 

• Forage 

• Sulphate in drinking water 

• Supplementation 

Daily dry matter intake, animal class and liveweight also affect the overall nutritional picture. 

Practical reference values for beef cattle are around 1.5–2.0 g of sulphur per kg of dry matter intake. These are total-diet reference values, not fixed supplement targets.  

Total sulphur intake from forage, drinking water and supplementation needs to be considered together. Excess sulphur intake can negatively affect animal performance and may increase the risk of polioencephalomalacia (PEM). 

The objective is therefore not to add as much sulphur as possible. 

The objective is to fill the gap between what the diet already supplies and what the animal requires. 

A simple sorghum example 

Consider a 400 kg steer eating approximately 10 kg of dry matter per day. 

If the forage contains around 0.10% sulphur, the forage itself supplies approximately 10 g of sulphur per head per day. 

Using a total dietary reference range of approximately 15–20 g per day, that leaves a potential gap of around 5–10 g per head per day.  

But forage is not the only source. 

Drinking water can also contribute sulphur, depending on its sulphate concentration. Groundwater sulphate concentrations in northern Australia can vary considerably, with average concentrations reported at around 400 mg/L. 

For example, if that same steer drinks 30 L of water per day containing 400 mg/L sulphate, the water would provide approximately 4 g of sulphur per day. 

In that scenario, forage and water together provide approximately 14 g of sulphur per day. The remaining gap would therefore range up to 6 g per day, depending on the animal’s total requirement. 

That changes the supplementation question. 

Rather than asking: “How much sulphur should I feed?” 

The better question is: “How much sulphur does this animal already receive, and how much do I actually need to add?” 

That distinction helps avoid both under-supplementation and unnecessary sulphur intake. 

The challenge is not only what you feed. It is what each animal actually gets. 

Once the nutritional target has been established, delivery becomes important. 

With a voluntary loose lick, individual intake can vary between animals. A shy feeder may consume very little, while a dominant animal may consume considerably more. 

That creates a practical challenge when the objective is to bring total dietary sulphur into a defined range. 

Water delivery takes a different approach. 

With uPRO FORAGE through uDOSE™, the product concentration in the drinking water can be set and adjusted. Every animal drinking from the trough receives water at the same product concentration. 

However, there is an important distinction: 

The concentration is controlled, but daily product intake still depends on water consumption. 

That is why actual water intake needs to be considered when setting the rate.  

The important point is that the rate should be considered in the context of the whole diet, rather than selected in isolation. 

Don’t overlook sulphate in the drinking water 

Forage is not the only part of the diet that needs to be assessed. 

Drinking water can contribute to total sulphur intake when it contains sulphate. The amount needs to be measured and included when calculating the overall sulphur budget. 

A water analysis should include sulphate and TDS, alongside other relevant minerals.  

This is easy to overlook when calculating supplementation from forage analysis alone. 

The practical approach is simple: 

Test the forage. Test the water. Then calculate the supplement requirement. 

Sulphur does not replace sorghum risk management 

This point is critical. 

Sulphur supports the animal’s normal pathway for converting absorbed cyanide into thiocyanate. It is not an antidote and it does not make hazardous sorghum safe. 

Sorghum grazing management should therefore remain part of the program. 

Practical measures include: 

• Do not turn hungry cattle onto sorghum. 

• Delay grazing until plants are at least 50 cm high for short varieties and 75 cm high for tall varieties. 

• Avoid or tightly manage young, wilted, frost-affected or stressed regrowth. 

• Test higher-risk forage where appropriate. 

• Monitor crop condition. 

The nutritional picture can change as the crop matures 

Sorghum does not remain nutritionally identical throughout the grazing period. 

As the crop matures, fibre, digestibility, protein and energy supply can change. Water consumption and animal performance can change as well. 

For actively growing green sorghum, the focus may be on sulphur contribution, mineral supply and water intake. 

As the crop matures, forage DMD/ME, crude protein, actual water intake and animal performance become increasingly important. 

For dry sorghum stubble, the main nutritional constraints may be different again. 

The decision should therefore be based on feed analysis and the production objective, rather than simply the calendar date.  

How to build a sorghum supplementation program 

Before setting a final uPRO FORAGE rate, DIT AgTech recommends assessing three areas. 

1. Test the forage

Where relevant, the analysis should include: 

• Dry matter 

• Crude protein 

• DMD/ME 

• Sulphur 

• Phosphorus 

• Calcium 

• Magnesium 

• Relevant trace minerals 

2. Test the drinking water

Assess: 

• TDS or salinity 

• Sulphate 

• Sodium 

• Other relevant minerals 

• Potential seasonal changes 

3. Define the cattle and production target

Animal class, average liveweight and production target should all be considered before finalising the program.  

From there, the total diet can be assessed and the uDOSE™ rate set. 

A practical way to think about sulphur 

The key takeaway is simple. 

More sulphur is not automatically better sulphur. 

For cattle grazing forage sorghum, the objective is to understand what is already being supplied by the forage and drinking water, identify the nutritional gap, and then supplement appropriately. 

The delivery method also matters. A voluntary supplement can result in variable intake between animals, while controlled delivery through drinking water provides a consistent product concentration. 

Want to see the numbers? 

We’ve put the calculation into a one-page fact sheet, including a worked example showing how forage sulphur, supplementation and total dietary sulphur fit together.