Hoose disease threat increased after wet summer

Veterinary advice for farmers

After a wet summer. grazing cows are picking up more lungworm larvae than usual.

Jacky was on the phone again recently.

His cows were still coughing.

We had carried out some blood tests and faecal sampling six weeks ago.

The recommendation at the time was to dose them for lungworm.

As you would expect, there was an initial period of increased coughing, which receded, but there was still a residual low-grade cough, and Jacky had started to find the milk yield going backwards.

A date was arranged to carry out some lung washes in order to get a better look at what was going on.

These cows had been given their usual vaccination for IBR in June.

At the same time, I was reading a very good article by Ruth Vernon, BVSc, Cert CHP, MRCVS, on the available solutions for the lungworm problem in dairy herds.

According to her, the risk factors for lungworm are:

n 1. Wet summers.

n 2.Heavy stocking rates.

n 3. Poor development of immunity.

I think we can all identify with the first two risk factors.

This summer, after a very promising opening during the month of May, descended into a fairly wet and humid June and July.

This type of weather, allied with the increased stocking rates of recent years, really helps the life cycle of the lungworm.

Because of the increased stocking rate, there are a lot more faeces left in the paddock after the visit from the cows.

The wet weather allows the lungworm larvae to survive longer on the ground.

It also helps release them much easier from the cowpat and together with the increased humidity and temperature, there is an increased growth of the Pilobolus fungus on the cowpat, which actually flings the larvae away from the cow pat, giving a much greater ground coverage than would be the case in dry conditions.

The larvae sink to the lower parts of the grass plant, and the modern trend of letting cows graze down pasture to lower levels means that these lungworm larvae are now much more accessible to the cow than previously.

The third risk factor that Ruth has marked out is the poor development of immunity in our animals.

This can be due to a number of possible causes.

Youngstock can develop immunity to the lungworm larvae that they ingest, if the level they ingest is at a low number.

Over the last 20 years, we have encouraged a culture of over-dosing, so we do not allow this immunity a chance to grow.

The result is cows that have no immunity against the lungworm larvae, and anthelmintics that have lost their efficacy.

We have landed ourselves in a major problem.

There is, however, a vaccine available which can instil this immunity into our animals before they hit the pasture.

Like a lot of vaccines, it requires two initial doses, and a possible yearly booster.

The vaccine is given by the oral route on two occasions, four weeks apart, and needs to be given at least two weeks before going out to grass.

Calves need to be at least eight weeks old before they get the first dose so, doing the sums, they will be 14 weeks old before they reach grass.

This may be fine for the early calf but can be a problem for the later calf.

If you are going to use the hoose vaccine, then you need to have a chat with your vet, because the success of using this vaccine depends on a lot of factors, like the correct storage and administration of the vaccine; when the animals are released to pasture; and the type of pasture they are set to graze on.

Subsequent dosing regimens, and whether all the animals have been vaccinated or not, will have a major bearing on results.