Pasture Chloride Levels and Heat Stress

Chloride is an essential nutrient that all plants and animals require. It’s extremely well recycled in the environment and as such it’s rare to see chloride deficiencies amongst grazing animals. However, this recycling can lead to an accumulation of chloride with excessive herbage chloride levels contributing to risks to animal health in the summer.

What’s the Risk?

Pasture chloride levels in excess of 1.6% reduces the animal's ability to sweat and as such controlling their heat load on hotter days becomes a problem. Cows may be seen to open mouth breathe (pant) particularly on herding which is a sign of heat stress. When heat stress risk factors such as high air temperatures, high humidity or low air movement are present, high chloride levels will impair the animal’s ability to cool itself with heat stress becoming an issue particularly on the walk to the shed on hot afternoons. Heat stress will reduce intakes and reduce production as well as making cow’s difficult to move.

So how do we prevent this?

To understand how to prevent excessive chloride levels in pastures first we need to know where the chloride is coming from. Natural inputs of chlorine to our soils include rainfall, sea spray and pollution, and unfortunately, we have little control over these factors. However, chloride can also accumulate from the use of chloride containing fertilisers or irrigation water. The most commonly used chloride containing fertiliser is MOP (Potassium Chloride). In fact, fertilising with 80kg/ha MOP will result in application of 37.6 kg/ha of chloride. Other common chloride containing fertilisers include Ammonium Chloride (NH4Cl), Salt (NaCl) and Magnesium Chloride (MgCl2).

Knowing the chloride levels of your pastures means you can determine the risk your herd faces and put in place appropriate strategies to reduce the risk associated with high levels. For example:

• If high levels are associated with proximity to the ocean (ie. Salt spray input) then grazing stock on more distant paddocks (with lower Cl content) of the farm on hot days/summer months may be helpful.

• As a longer-term strategy, if excessive chloride levels are a result of fertiliser inputs, determining fertiliser requirements in response to soil and pasture levels on your farm may allow you to reduce these inputs.

• Using alternative, non-chloride containing fertilisers will also help lower the risk of high pasture chloride levels.

• Provision of shade, good fresh water without excess solutes (magnesium and zinc products) and perhaps even sprinklers in the cow yard will all be helpful.

Chloride is a good example of why all nutrients in our farming environment should be considered, even those that aren’t often seen as an animal health risk. Using an Animal Centered Approach means barriers to desired outcomes (ie. Milking & reproductive goals) are identified and addressed, and your farm environment is optimal for both pasture growth and animal health.

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