Stone mad: why drought causes strange behaviour in livestock

Drought had firmly set in many parts of the country before some badly needed rainfall over the weekend.

On Friday, soil moisture deficits were running at up to 75mm in places. Grass growth was almost negligible, and what was growing was heading out early and is often of poor quality.

This is affecting milk yield in dairy herds and daily live weight gain in beef herds.

One of the health issues that we are seeing a lot more of in this time of drought is Pica

this is the persistent chewing, licking or eating of unusual things such as soil, stones, wood or plastic. Over the past few days, we have received a number of calls from puzzled farmers relating to this condition.

“They are gone mad chewing stones and trying to eat the water pipe,” one farmer complained.

“They’d eat the shirt off your back if you stood still for long enough,” another client said.

The animal displaying this type of behaviour is doing so for a reason to try to correct some type of deficiency or something that is lacking in their diet.

There are three main causes of pica: lack of fibre in the diet, salt deficiency or phosphorus deficiency.

Lack of fibre

Fibre is essential for good rumen function and health.

The lush leafy pasture that cows normally graze at this time of year can be very low in fibre. The result is that cows get very loose in the dung. The will develop dirty, wet tails and often, farmers will complain that the dung appears to have bubbles in it.

The main indicator of low fibre in dairy cows is a drop in butter fat percentage. The lack of fibre causes a condition called SARA (sub-acute rumenal acidosis). Poor fertility and a drop in milk yield are a direct consequence of this.

It is easily rectified, however, by adding fibre to the diet, in the form of straw or soya hulls.

Given that at present, what grass is available is far from lush or leafy, lack of fibre can, for the most part, be ruled out as a cause of pica.

Salt deficiency

Lack of sodium causes pica, along with reduced water intake. If a cow’s water intake is reduced, then her milk production will reduce dramatically.

The most common sign of salt deficiency is licking or drinking urine. It is most obvious in indoor cattle as they can be heard slurping from the floor before you even see them.

The interesting thing about sodium is that it is self-regulating in cattle if a cow has enough in the diet, she will not seek out any more.

I find salt licks to be the easiest form of supplementation. Usually, at the start, they will devour the licks, but as the levels approach normal, they will eat less and less.

Phosphorus deficiency

This has been the most consistent cause of pica, particularly in dairy cows, that we have diagnosed recently.

We have seen phosphorus deficiency on farms lately with a soil index of 3 for phosphorus based on last year’s soil samples. This is because drought conditions affect the uptake of phosphorus from the soil by grass.

Acute phosphorus deficiency can present as a sudden, dramatic reduction in milk yield. The red blood cells in the cow’s body can burst, leading to red-coloured urine, similar to that of an animal with redwater.

This acute condition can be fatal, so immediate veterinary attention is vital.

With the more chronic type of phosphorus deficiency, we see cows eating stones, pipes and plastic. This too causes a reduction in milk yield and also can lead to poor fertility.

At present, where droughtaffected grass is low in phosphorus, the cows can rely on their internal stores to make up the deficit for a short period. A cow needs around 70gr per day of phosphorus, so reserves are quickly depleted and clinical signs set in.

Supplementation in required to rectify the problem. We favour application of a liquid phosphorus solution to the drinking water twice daily. This has to be done for at least 10 days as it takes time for the levels to normalise in the cow.

By the time you read this, hopefully a lot of muchneeded rain will have fallen. Cows can go back to eating lush green grass and not water pipes and stones.

Eamon O’Connell is a vet with the Summerhill Veterinary Clinic, Nenagh, Co Tipperary

Thirsty work:

An adequate water supply will stave off the worst effects of drought on cows, but they may also need salt and phosphorus supplementation to maintain milk yields

Acute phosphorus deficiency can present as a sudden reduction in milk yield