Scouring Ruminants

Johnes Disease is caused by a bacterial infection Mycobacterium avium paratuberculosis usually shortened to Map. At best the prevalence of the disease in the UK is only an estimate as nobody is monitoring the number of cases that occur. Often it can be present, but go unrecognised. It is estimated using data from other countries that as many as one in five dairy and beef cattle herds may be affected. In the past five years the numbers of diagnosed cases have more than doubled to more than 2,500. Sheep, goats, deer and wild life particularly rabbits can also get Map. It is difficult to positively diagnose in sheep as they carry few organisms when they are infected and do not show any changes in their blood.

Getting Infected

The exact course of the infection is unclear. It is thought that most animals are infected in the first two months of life. The bacteria get established in the small intestine where they are taken up by M cells. Young animals have more M cells than adults. In young animals milk goes past the immature rumen direct to the small intestine so there are more opportunities for the infection to get established. It is not easy to detect this initial infection by examining either faeces or blood. Most animals with a healthy immune system will eliminate the bacteria from their gut. It is thought that only 10 – 15% go on to develop clinical disease. Usually animals take two to six years before they will become ill and scour with the disease. Animals that carry the disease have the bacteria in their faeces. The challenge to young animals can be reduced if calving and lambing pens are kept clean. Water troughs should be cleaned from time to time to make sure that they are not contaminated with faeces.

Slow Build up

During this long latent period the animal is shedding the infection and contaminating the fields and sheds that they go in. Because the small intestine is damaged affected cows will not milk as well as expected so their calves will not grow as fast as they could. In affected herds there is a tendency for increased cases of metritis and mastitis. Many dairy animals with Map are culled for other reasons before they have a chance to scour with the disease. It has been found that sheep in the early stages are more prone to worm and fluke infestations. This can sometimes be used as an indication that Johnes disease is active in a flock.

Johnes Disease in Sheep

I am bringing all of this to your attention because last month, for the first time we came across a ram that died of Johnes disease, there were certainly suspicious organisms in the faecal sample. Most years there are only 100 suspect diagnoses of Map in the whole of the UK so it does not occur very often. Hopefully he has not introduced the problem to the rest of the flock. We will certainly be looking for the tale tells signs and I will let you know if it manages to get established on the farm.

Blackleg

Also last month we came across another bacterial disease that is still all too common. This one can also survive in the soil for long periods. In contrast to Johnes disease it is characterised by the rapid way that it can cause problems. Clostridium chauvoei can be found in the small intestine of healthy cattle and sheep. It starts to cause trouble in young animals when there are too many bacteria present. It is dangerous when it moves from the gut into the blood stream and settles in the muscles of the leg or in the heart muscle.

Clinical Signs

Very occasionally there is an opportunity to treat cattle with blackleg, they have a high temperature and are usually very sick and reluctant to move around. Even with high doses of penicillin it is difficult to keep them alive. Like many of the clostridial diseases it is the calves that are doing well that are the most likely to die with the disease. At post mortem they are found to have areas in the muscle that are dark red and spongy, small gas bubble appear and the carcass will decompose rapidly.

This is what muscle looks like when an animal has blackleg.

Beef animals between six months and two years of age are the most likely to die with black leg.

Control of the Disease

Groups of animals with horns are particularly vulnerable as they tend to damage themselves and this can bring on the symptoms. When losses occur it helps if you can move the group onto another field where there is not so much grass. The vaccines are effective and usually a single injection each year will provide sufficient protection. At times of severe crisis penicillin can be given at the same time as the vaccine to reduce the number of bacteria in the gut and in the blood stream.

New Mastitis Tube

Norbrook have developed a new lactating cow tube that looks interesting. It is a combination of Trimethoprin and Sulphadiazine, drugs that are not found in any other mastitis tube. It has a broad spectrum of activity so it will combat Strept uberus as well as E coli infections. This new tube has a rapid mode of action that peaks at six hours after insertion and has more or less gone from the udder after twenty four hours. The tubes should be given for three milking. It has a rapid milk withhold of 48 hours and is unlikely to cause residue failures if it is used in the correct way.

Hospital Bugs

You might be interested to know that the infections that are difficult to deal with in hospitals do occur from time to time in animals as well. Methicillin resistant Staph aureus is a variant of the bacterium that can cause high cell counts in cow’s milk. It is a skin organism that can progress unchecked as it is not sensitive to many antibiotics. It does not appear to be a particular problem on farms and it not readily passed on to people. Dogs and cats can have it on there skin. It has been known to cause problems after surgery although it is unlikely to get established if sites are prepared carefully with the liberal use of iodine scrubs and surgical spirit. We have never had a positive diagnosis from samples that we have investigated.

Clostridium difficile is a recognised pathogen of young pigs and horses. Affected animals do not respond well to treatments as they are often already on antibiotics and may have been suffering from other diseases before the clostridial infection became established. The bacteria can be found in the gut content of healthy animals. This does not appear to be a problem with companion animals although they must be exposed to the infection.                 

Return to Newsletters