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Grass growth spurt after a drought can present a range of problems

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Eamonn Connell

Eamonn Connell

Grassroots issue: Grass tetany is a condition usually seen in spring when cattle are adjusting to the outdoor diet, but it can also surface when summer grass growth resumes after a standstill due to drought. The condition is caused by magnesium deficiency and can be fatal if not treated.

Grassroots issue: Grass tetany is a condition usually seen in spring when cattle are adjusting to the outdoor diet, but it can also surface when summer grass growth resumes after a standstill due to drought. The condition is caused by magnesium deficiency and can be fatal if not treated.

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Eamonn Connell

The rain has finally arrived and grass growth has returned with a bang.

But grass growing quickly after a period of drought, although hugely welcome, can cause conditions that are not seen usually at this time of year.

Grass tetany

We are all familiar with this potentially fatal condition caused by a deficiency of magnesium in the diet.

Muscle twitching progresses to staggering, recumbency, seizure and ultimately death if not treated.

It is usually seen in the spring, when grass is scarce, temperatures are quite cold and cows are adjusting to the outdoor diet.

However, when grass growth is at a standstill and then suddenly is kick-started by the rain, tetany can be an issue.

When it rains heavily, the potassium from fertiliser or slurry is taken up more rapidly by the fast-growing grass than magnesium.

There are still a number of cows bulling at present too. The high activity and the low feed intake of a bulling cow will increase her risk for developing tetany when grazing these fast-growing pastures.

A lot of concentrate has been fed over the past few weeks to try to keep cows milking while grass is scarce.

The temptation now is to cut back as grass becomes more readily available. It is well worth continuing to feed for another week or so until grass becomes properly established.

Concentrate provides energy and added magnesium. Rumen health and pH are already affected by the lush grass.

Cutting back concentrate will only exacerbate this, greatly increasing the risk of tetany.


Copper deficiency

As the countryside turns green, I see more and more calves turning brown. It is a problem every year, but speaking to vets around the country, it seems to be particularly common at the moment.

Rapid grass growth after rain leads to reduced copper concentration in pasture.

Along with lack of copper, excess molybdenum reduces the availability of copper in the rumen. Application of lime, although hugely beneficial to grass growth, also has the affect of releasing more molybdenum from the soil.

A dusty brown-coloured coat, particular noticeable in black cattle, is the classic symptom. Others include lameness and poor thrive in cattle, and swayback in sheep.

Supplementation is by bolus, injection or it can be added to the water supply. Sheep can easily suffer from copper toxicity, so supplementation should only be carried out in consultation with your vet.

Cobalt (Vitamin B12) deficiency

As the grass growth returns, calves and lambs will start to grow rapidly on the lush grass.

These animals, particularly lambs, have a high demand for cobalt, and there may not be enough in the diet at present.

Signs of cobalt deficiency include poor thrive, poor appetite and pica (eating random objects).

Blood samples are needed to confirm the condition. Supplementation can be in the form of boluses, injection or a drench.

CCN (Vitamin B1 deficiency)

Vitamin B1 (Thiamine) is normally produced by bacteria in the rumen of healthy cattle.

A balanced diet containing lots of fibre is necessary for a healthy population of rumen bacteria.

The fast-growing, lush grass being eaten at present is low in fibre and far from ideal for rumen health. Calves in particular are most likely to suffer from a disturbance in rumen flora, resulting in a decreased availability of Vitamin B1.

Signs of B1 deficiency include blindness, circling and increased sensitivity to sound and touch. This will progress to seizures and death if not treated.

Supplementation of fibre over the next few weeks will help keep the rumen healthy. This will not only help prevent B1 but will also help keep summer scour syndrome at bay.

If increasing concentrate levels, do so very gradually to give the rumen time to adjust.

Eating fresh ferns has also been linked to cases of CCN. Ferns have shot out of the hedges over the past week, so keep young stock fenced away from them where possible.

Lungworm will become a problem over the next week or two so I’ll open that rather large can of worms next week.

Although the end of the drought has brought fresh animal health issues, it is still far better than buffer-feeding silage and watching paddocks burn up.

Who ever thought we would be delighted to see deluges in June?


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

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