Controlling Lungworm

The adult worms of Dictyocaulus viviparus live in the larger airways of the lungs of cattle. Ingested larvae work their way through the lining of the gastro intestinal tract to find the lymphatic system of their host so that they can be taken on to the lungs. After three weeks they start to lay eggs that immediately hatch into the first stage larvae and move up the air way to the mouth where they are swallowed to pass the full length of the digestive tract.

Treatments

This is a complicated life history and because the third stage larvae pass through the tissues of the host there are good opportunities for the cow to develop immunity to the parasite. Young animals are particularly at risk because in their first grazing season as they will have no defences against the invading larvae as they are unable to respond quickly enough if they take in significant numbers of the parasite.

There are no reported drug resistance problems for lungworm. Modern wormers are very efficient and most are able to eliminate all of the adult lungworm from the airway after a single treatment. Unfortunately that does not resolve the problem because it does not give the host enough time to develop an effective immunity to the infection so they will show signs of disease and weight loss later in their lives. The characteristics of this disease has changed, it is more likely to be diagnosed in cows than young cattle and will cause production losses throughout the lifetime of a cow.

Vaccination

The vaccine is still available and it works well as the irradiated larvae that they send you cannot get to the adult stage in the lungs but will trigger the immune response that will normally last for the full life of the animal. Two doses are requires four weeks apart and it is better if the treated animals can be turned out to grass two weeks after the second dose to reinforce their immunity.

Bovine Viral Diarrhoea

BVD is a viral disease of cattle caused by a pestivirus. It has many different manifestations in a herd, depending on the immune system and reproductive status. Transient diarrhoea, mixed respiratory infections, infertility or abortion and mucosal disease are the most common clinical signs of the disease. Due to its varied manifestations and sub clinical nature in many herds, the significance of the disease has not been understood until recently, when diagnostic methods improved.
Currently, BVD virus infection is considered to be widespread in the UK cattle herd. There is no active surveillance. In 1998 a survey of over a thousand cattle herds in England and Wales revealed that 95% were affected by BVD.

Signs of Disease
Apart from causing an outbreak of acute diarrhoea at the time of introduction into a herd, the following short and long-term effects are caused by a herd infection: infertility, embryonic death, foetal mummification, abortion, congenitally damaged calves and persistently infected (PI) calves that are likely to die of mucosal disease before two years of age. BVD virus has also been identified as an immunosuppressive agent, increasing the risk of infections such as respiratory disease in calves, salmonellosis, interdigital dermatitis, mastitis and post calving infections.
Tracing the Source
As you know there are vaccines available that help to reduce the losses from BVD but they do not get rid of the persistently infected cows that generate the infection. The statistics show that BVD is not a disease that you can easily control on an individual farm. When the test to detect Persistently Infected animals was first introduced the laboratory costs were discounted and affordable so that it was often possible to blood test all of the adult animals in a herd and identify the ones that were carrying the virus. Sadly with larger herd sizes and more movement of animals between herds this strategy is now an expensive option.

Control Scheme in Scotland

I have always thought that the only way to really control BVD is for all cattle owners to be involved. I am encouraged to hear that the Scottish Government is proposing to introduce a mandatory annual blood test for all breeding cattle. The plan is that from September 2012 it will not be possible to sell breeding cattle from farms in Scotland unless it can be demonstrated that they are free from the disease. There will be no compulsory slaughter scheme for infected individuals, but it is inevitable that market forces will eventually lead to a substantial reduction in infected herds.

No Controls in England

It is encouraging that despite the difficulties and at a time of economic restraints the Scottish Government has the forethought to bring in measures that will eventually give long lasting benefits to all cattle farmers in Scotland. There are no indications that DEFRA would ever be able to introduce a similar scheme in England.

Unusual cause of Mastitis

We all get familiar with the usual suspects that are the cause of mastitis and high cell counts in dairy cows. From time to time you might get an acute case or come across an infection that is particularly difficult to treat and take samples so that we can work out the best way to tackle the problem. Most of the culture results we get are Staph aureus, Strept uberus, Strept agalactia or E coli. Just occasionally other bacteria can cause problems in dairy cows. At the moment we are troubled by a bacterium that is the cause of only a subtle change in the look of the milk, but it does cause a dramatic rise in the cell count. It has taken more than two weeks for these bacteria to be identified as Streptococcus canis. The infection is carried by dogs and cats in their faeces and nasal excretions. So far we have had some success by pre dipping and adhering to strict hygiene protocols when the cows are milked. Saw dust is used on the beds and although it is not thought that much of it has been visibly contaminated this is probably the source of the problem.

Itchy Sheep

This winter so far has been colder than those of recent years and it has been noticed that there are more flocks trying to cope with sheep scab. For some reason sheep with scab seem to start rubbing around the time that they are due to lamb. This is the time when you are busy and they are most difficult to treat. Sheep with scab tend to get severe flaking on the skin and they will readily damage themselves. We can usually tell fairly easily what is making your sheep rub if you can bring in some wool samples. The best samples are to pluck wool on the edge of the lesions away from the head. Take five or six plucks and bring them to the Surgery. We have found that young lambs do not usually get scab from the ewes and it is better not to treat them less than two weeks of age unless they are showing lesions.

Return to Newsletters