Salt supports better pasture utilisation and higher milk production

The problem in New Zealand

Most New Zealand pastures supply plenty of potassium, but very little sodium. Potassium is boosted further when potash fertiliser is applied. Sodium is rarely added to soil or pasture, so it often sits below the level cows need for best performance.

Potassium content of New Zealand pastures often sits above the ideal level for dairy cows.

Why this matters for cows

A sodium shortage and high potassium load affect how cows eat, digest and perform. On farm this can show up as:

• Lower appetite and poor clean up of pasture
• Reduced milk production as cows cannot fully use the energy in the feed
• Fertility challenges during early and peak lactation
• Higher risk of metabolic issues and animal health problems

Sodium is central to fluid balance, nerve function and rumen performance. When sodium is low and potassium is high, cows need to work harder to maintain balance. They often respond by eating less.

The result is a pasture system that looks productive on the surface, but delivers less than it could in milk solids.

As potassium rises, feed intake and milk production can fall if sodium intake is not lifted as well.

What causes the imbalance

The key issue is the interaction between potassium and sodium in the plant, in the rumen and in the cow.

• High potassium in pasture makes it harder for cows to absorb and use sodium.
• Low sodium in soil and pasture means cows start short before the season even gets going.
• The more starch, sugar and lactic acid that are fed, the more sodium chloride is required to help maintain rumen function and overall balance.

It is important to keep the ratio of potassium to salt within an ideal range to support intake and milk.

How salt fixes the problem

Adding salt is the simplest way to lift sodium intake and balance the effect of high potassium. Research and farm experience show consistent gains when sodium chloride is supplied at the right rate.

Key benefits of using salt with dairy cows

• Improved appetite and higher dry matter intake
• Better pasture clean up and fewer clumps or rejection patches
• More persistent milk curves through the season
• Support for fertility and overall cow health
• Better use of existing pasture and supplements

As potassium and fermentable feed load increase, salt requirements rise as well.

How to use salt on farm

There are two main ways to use salt in pasture based dairy systems: directly in the diet, and on the pasture itself.

1. Feed salt directly to cows

• Include finely ground salt in blends, pellets or mineral mixes.
• Dust salt over silage or other supplements where practical.
• Provide controlled access to suitable salt blocks when appropriate.

2. Apply salt to pasture

• Open salt rate calculator
• Focus on times when growth and potassium are high, or when intakes are disappointing.
• On free draining soils, consider more frequent, lighter applications so that sodium remains available.

When to increase salt use

• After potassium fertiliser applications.
• When cows are not fully cleaning up pasture.
• When milk production drops without an obvious explanation.
• During periods of high starch or sugar feeding where rumen balance is under pressure.

Salt product options

Different farm systems and feeding setups call for different salt formats. Common options include:

• Feed grade fine salt for inclusion in blends, premixes and on feed.
• Coarse agricultural salt for pasture spreading or dusting on silage.
• Mineralised salt blocks where sodium and key trace elements are required together.
• Specialty blocks and licks for targeted use in specific classes of stock.

Your local merchant, fertiliser representative or nutrition adviser can help match product type and rate to your pasture, cow and system needs.

Research evidence and New Zealand data

International research and New Zealand pasture surveys support the role of sodium chloride in balancing high potassium systems. Meta analyses and controlled trials show that when sodium is lifted to appropriate levels, cows eat more, perform better and utilise pasture more evenly.

New Zealand pasture sampling frequently finds potassium levels at or above three percent in many systems. This sits above the ideal range for dairy cows if sodium intake is not increased at the same time.

Many New Zealand pastures sit above the ideal potassium band for cows for long periods of the year.

Key takeaway

Resources and next steps

For more detail on application rates, pasture responses and the science behind sodium and potassium balance, explore these resources.