Cattle and salt: the good, the bad and the ugly

Cattle and salt: the good, the bad and the ugly

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THIRSTY: How oral electrolytes work. Picture by Zoe Vogels.

THIRSTY: How oral electrolytes work. Picture by Zoe Vogels.

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Vet Zoe Vogels explains how salt affects cattle, both good and bad.

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There are two benefits to having the kids schooling at home: one is not having to make school lunches, the other is being involved in learning new things.

Watching a ryegrass seed germination experiment on the windowsill has given me a new appreciation of the effect of salinity on pasture growth (for the record, greater than 0.5 per cent salt water is not good!).

It also inspired the topic of this column: how salt (sodium) can affect cattle health.

Saline soil or water impairs seed germination and plant growth due to osmosis, the process that drives water through a membrane from the side with low salt concentration to the side with high salt concentration to obtain the same concentration on both sides; rather than plant cells absorbing water, water moves out of them instead.

Sodium concentration is also the main driver of water movement between body fluids (such as blood plasma) and body cells (red blood cells, for example).

Sodium and the principle of osmosis can be used for good when managing scouring calves who can lose significant volumes of fluid and are often 5-10pc dehydrated.

In the intestines, sodium and glucose are actively absorbed together and this absorption of sodium draws water in, too.

Milk contains relatively little sodium, so feeding scouring calves oral electrolytes with the correct amount of sodium and glucose increases water absorption and corrects dehydration.

Potassium and alkalinising agents are other essential ingredients of oral electrolytes - ask your vet which products are best to use.

What about the bad and the ugly?

There are two ways that salt balance can cause disease in animals.

The first, if their feed or water is very salty, is from a direct overload and osmosis draws water out of body cells to even out the salt concentration in the body fluids.

In the brain, neurons become dehydrated and low in energy and animals show neurological signs, ranging from depression and incoordination to convulsions, coma, and death.

Animals can also have diarrhoea from intestinal irritation and the osmotic effect of the salt.

Instances have included beef cattle drinking from bore-filled dams where evaporation has occurred, calves fed milk replacer prepared with bore water without access to fresh water, and animals exposed to salt licks after periods of salt deprivation.

The second way salt causes toxicity is indirect and occurs where animals suddenly have unlimited access to fresh water after a period of water deprivation.

During water deprivation animals become dehydrated, the salt concentration in body fluids increases and water is slowly drawn out of body cells to equalise the salt concentration.

In this scenario, neurons have time to try and avoid osmotic dehydration by actively increasing their own salt concentrations.

Problems arise when a thirsty animal suddenly drinks a lot of water, which then moves into the neurons, causing them to swell.

The resulting cerebral oedema and increased cranial pressure cause neurological signs such as stargazing, tremor, blindness, convulsions, and death.

Red blood cells can also swell and burst from the influx of water and animals may have red urine.

To minimise the risk of this indirect salt toxicity, it is important to identify that water deprivation has occurred and to introduce water slowly over a few days.

Animals should be offered their daily water requirements (roughly 10pc of bodyweight plus 85pc of milk volume for lactating cows) in six feeds throughout the day.

This allows for gradual water movement to even the salt concentration throughout the body and the brain rehydrates without the oedema.

To sum up, the key to reducing the risk of salt toxicity is ensuring stock always have free access to water (ideally less than 0.5pc or 5000 ppm salt).

Know the salt content of available feed and water to identify potential problems early; take care introducing salt to salt-deprived animals.

And, for scouring calves, mix oral electrolytes as per instructions with fresh water, not bore water or milk.

About the author: Dr Zoe Vogels is a veterinarian at The Vet Group, Timboon.

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