Why control Johne's disease?
If uncontrolled, Johne's disease will have a financial impact on your dairy business. Particular impacts include:
- Milk production may be impaired before other clinical signs are evident, but the loss of production may not be recognised as due to Johne's disease. In the lactation in which signs of the disease become apparent cows can produce 25% less milk than their potential yield. In the lactation before this the reduction is 10%. By the time signs of diarrhoea and wasting are clear, milk yield will be significantly affected. Your total milk yield and thus income from the herd could be significantly decreased.
- Infected cattle are more susceptible to other diseases such as mastitis and, because they have difficulty maintaining body condition, their fertility is poor. Treatment of these conditions is expensive, and you will have to consider the costs of replacing culled stock.
- The capital value of your breeding stock could also be reduced if there is demand for stock or milk from herds that can be certified as tested free of Johne's disease.
Three Good Reasons for controlling Johne's disease
Control and prevention of Johne's disease makes sound long term sense for three reasons:
- To reduce or prevent your production losses and income that result from this disease;
- To increase the value of your breeding stock if your herd is certified as free of the disease;
- To reduce the level of Map in milk and the environment.
Screening your herd for Johne's disease
Because it takes a long time for signs of Johne's disease to appear in infected cattle, you may not know that it is present in your dairy herd. It is very important to look out for signs of the disease and advisable to take steps to screen the herd for the presence of Map. This will help you and your veterinary surgeon decide the best course of action, particularly in preparing a herd health and welfare plan.
Once an animal has severe diarrhoea and is losing weight the disease can normally be readily confirmed by a blood test or by microscopical examination of the dung. The Map organism can be cultured and identified from the dung, but it takes up to six months to obtain the result - too long for this to be useful for the routine diagnosis of disease. However diagnosis of the presence of the organism in animals in the silent period of the infection, before signs become apparent, is difficult. Infected cattle seldom pass detectable numbers of Map in their dung until they are beyond two years of age.
There is a blood test that detects the antibody to Map produced by infected cattle. However, cattle tend to produce the antibody to Map relatively late in the infection. In some individuals it may be difficult to confirm the presence of infection in the live animal. Where an infected animal is tested throughout its life it can be expected to test negative on one or more occasions before it tests positive. This also means that testing apparently healthy animals at the point of sale or on arrival in their new herd cannot guarantee prevention of the introduction of infected animals to the herd.
Taking these realities into account, you should consult your veterinary surgeon to develop a screening programme that best suits your business needs. For instance:
- If you believe your herd is not infected and you wish to provide a high level of assurance for certification to support sales, a regular testing programme may be appropriate. This might take the form of a blood test every one or two years on all or part of the adult herd, combined with tests on any "suspect" animals or other culls;
- If you believe your herd is not infected but wish to ensure its early detection if it does occur, then tests on suspect cases, on culled cows, or periodic screening of a proportion of the older animals in the herd may be enough.
- If you know Johne's disease is present in your herd and want to try to eradicate it, a more intensive programme will be needed in conjunction with other management controls. Suitable testing programmes are provided by schemes that operate under the guidance of Cattle Health Certification Standards (CHeCS) for further information see www.herdcare.com/herdcare/index.html or www.cattlehealth.co.uk
Herd health and welfare plans
- It is good practice to implement a programme designed to reduce the chances of introduction of infection into the herd and spread of infection within the herd. This is true whether you know you have infection, or believe you may be free from it.
- It is very important to develop a health and welfare herd plan in conjunction with your veterinary surgeon.
- The control of Johne's disease on your farm needs to be considered together with the need to control other cattle infections. Improving or maintaining strict biosecurity can help control many diseases, as well as Johne's disease.