Farm Ireland

Tuesday 20 March 2018

Mineral deficiency can be a hidden killer in dairy herds

More than half of Irish pastureland is deficient in phosphorus and only 10pc is at optimium phosphorus and potassium levels.
More than half of Irish pastureland is deficient in phosphorus and only 10pc is at optimium phosphorus and potassium levels.
Vet Eamon O'Connell.

"I can't stand in the paddock with them because they'll eat the coat off my back," one farmer said to me recently about the unusual behaviour of his cows.

It was a statement that would not have been surprising had I heard it during the fodder crisis of 2012 and 2013.

However, it certainly causes some raised eyebrows in June 2016, with grass in abundance in many areas.

This desire for dairy cows to try to eat unusual items, well outside of their normal diet is, in fact, a symptom of an underlying condition - phosphorus deficiency.

In recent days I was called out to a severe case where the cow was constipated from eating so many sharp stones and she had blood in her urine. Unfortunately, she didn't respond to treatment and died overnight.

The farmer involved, Victor Austin, who milks 80 cows in Cloughjordan, Co Tipperary, started giving his cows 15ml of phosphorus in the water every day for 10 days, but it took the cows three or four days for them to stop eating unusual things. After 15 years milking, they had never encountered the problem as bad before.

"We'd notice the cows were eating the stones and they were at it for a while but we didn't take much notice until one got sick," he said.

Problems caused by mineral deficiencies include reduced weight-gain, decreased milk yield and poor fertility.

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Most cases of phosphorus deficiency however, can be diagnosed purely on clinical signs.

One of the most common signs of phosphorus deficiency is pica: a desire to eat things that aren't of any nutritional value. Cows with phosphorus deficiency will eat stones off the roadway, chew on water hosing and munch on insulators on fencing and twines holding gates shut.

Some cows can present with more acute and severe signs - very weak with a dramatic reduction in milk yield. These cows often have red coloured urine.

This can be confused with Redwater, the tick-borne disease, so it is important to get your vet involved. These cows can go downhill quite rapidly and some losses have been seen so early intervention is very important. Your vet will advise you on the herd health packages available and will tailor them to suit your herd.


Recent studies have shown that the phosphorus content of grazing pastures falls far short of what is required to maintain normal levels in the dairy cow.

Data on herbage from 102 farms showed that phosphorus levels were adequate on average, but there was a significant decline in phosphorus concentration during the mid-season coinciding with peak grass growth.

National soil fertility trends show that approximately 54pc of soils are deficient in phosphorus and that only one in 10 are optimum in terms of soil pH, phosphorus (P) and potassium (K). Some 89pc of soil samples tested by Teagasc were low in at least one of these measurements.

There has been a dramatic reduction in phosphorus fertilisers in recent years. It has been reported that the average phosphorus use on grazing ground has reduced by over 50pc in the past 10 years.

This is, in part, due to the nitrates directive but also, in the past, fertiliser was significantly cheaper.

Cows can deal with phosphorus deficiency for a while, but eventually, their reserves are depleted and problems begin to arise. Diagnosis of phosphorus deficiency is usually done by taking blood samples from eight to 10 cows.

If taking bloods, it can be useful to get a full mineral profile done to assess copper, phosphorus, iodine, selenium and magnesium levels in your herd.

Mineral deficiencies vary from farm to farm but it is important to know what is happening in your herd.

Eamon O'Connell is a vet at the Summerhill Veterinary Clinic in Nenagh, Co Tipperary

Soil sampling essential for prevention

Treatment of individual cows with phosphorus deficiency can be quite difficult.

The only available phosphorus injection was withdrawn from the market a few months ago.

However, we have been assured that a phosphorus injection will be available again in July.

These acutely affected animals may need oral fluids and in some cases, a blood transfusion. Recovery can be quite slow and these cows will often go dry.

Herd treatment of phosphorus deficiency is achieved by oral supplementation of phosphorus. This can be done by adding phosphorus to the dairy ration.

There is also a liquid phosphorus supplement that can be added daily to the drinking water.

Prevention of the clinical signs of phosphorus deficiency is somewhat more complicated.

Soil sampling and grass sampling are of great importance. Every dairy farmer should know the soil pH and the nutrient status of their farm.

It has been proven that soil pH can affect phosphorus availability.

By having the correct soil pH and an adequate level of nutrients in the soil, it will not only allow you to grow more, better quality grass but it will also enable you to prevent the problems associated with phosphorus deficiency.

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