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Infectious diseases

Course: Spring turnout management | Last Updates: 15th October 2015

 
Keith Cutler
Cattle Specialist
Endell Veterinary Group
Biography >>
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Infectious diseases are a serious drain on farm productivity and profitability, but are surprisingly common. For example, tests show 67% of dairy and 42% of beef farms in the UK have been exposed to leptospirosis. Two-thirds of dairy herds show evidence of infectious bovine rhinotracheitis (IBR), and an even greater proportion have been exposed to bovine viral diarrhoea (BVD).
These diseases have a variety of consequences resulting in a range of clinical signs, including reduced yield, fertility and abortions. BVD can also be considered a “gateway” disease, allowing pneumonia and other problems to take hold and wreak havoc with herd health.
Studies show a dairy herd endemically infected with BVD can be losing £63 a cow a year. Perhaps the greatest problem with BVD is that calves can be born with the infection (persistently infected or PI) and pass the disease on throughout their lives without it even being spotted. Leptospirosis has the added risk of human infection. But losses are unnecessary. Managing infectious disease requires a strategic approach. Implemented successfully, this can control or even eradicate a problem.

What are infectious diseases?

BVD is a viral disease that can be spread between animals, usually via nasal secretions. It can also be passed from mother to calf during pregnancy, resulting in the birth of a PI animal. Here, the immune system does not even recognise the virus as a pathogen, so a PI animal will carry and pass on BVD for its entire life.
The major effects of BVD are on the reproductive system, causing reduced fertility, embryonic death and abortions. It also causes immunosuppression, so any other diseases that may be present in a herd, such as pneumonia or mastitis, will be more prevalent and more severe if BVD is also present.
Leptospirosis is a bacteria that lives in the kidneys and reproductive tract and is usually spread in the urine. It causes milk drop, infertility and abortion. It is a zoonotic disease that can be passed to humans through urine splashes in the parlour, for example. It causes a nasty, and potentially severe, flu-like illness.
IBR is a viral disease most commonly spread in nasal secretions, but can also be spread in semen. It usually affects the upper respiratory tract but can also cause milk drop, infertility and abortions. Latently infected animals often remain undetected, but periods of stress can often precipitate disease, with affected animals appearing dull and listless and often showing signs of pneumonia.

How do they affect beef animals?

In a beef suckler herd, anything that affects a cow’s ability to get in calf or causes her to abort causes financial loss. Infectious diseases can result in reduced pregnancy rates and an increased number of abortions leaving more cows barren each year. They can also widen the average calving window beyond the 12-month optimum, resulting in an extended calving pattern. In store cattle, growth rates may be affected especially if secondary infection with pneumonia or other diseases becomes a problem.
 

How do they affect a dairy herd?

A dairy cow is like an athlete, constantly under pressure to perform. So anything that affects her health will cause milk drop. Infectious diseases will also cause a rise in embryo loss and a fall in conception rates.
Immunosuppression is a key feature of infectious diseases that can affect productivity in dairy herds. This can show itself through an increased incidence of mastitis and outbreaks of pneumonia in youngstock.
Problems can often be easier to spot in dairy herds through bacterial or somatic cell counts in milk, or a drop in yield. The dairyman usually has closer contact with these animals as they pass through the parlour.

Why are infectious diseases important at spring turnout?

The change of diet and environment that occurs at turnout alters daily routines and can increase stress levels, making animals vulnerable to infection. Turnout results in exposure to new threats. Parasites can also put animals, especially youngstock, under stress and IBR may be spread between herds following contact across boundary fences. Sheep can also be a threat as they can carry leptospirosis without showing signs of disease. Biosecurity should therefore be borne in mind.
Leptospirosis in particular can become an increased challenge following turnout. The bacteria that cause this disease reside in the kidneys and are shed in greatest numbers in neutral-pH urine. A silage-based diet results in an acidic urine, which suppresses bacterial excretion. The return to a grass-based diet at turnout results in an increased urine pH and increased bacterial excretion. The warmer, wetter conditions at pasture allow the bacteria to survive for longer, resulting in a greater challenge to the herd.
Another consideration, particularly in suckler herds, is there are frequently fewer opportunities to handle the animals after turnout to allow vaccinations to be given.

How do you plan to avoid problems?

A detailed risk assessment and considered healthcare plan, including an appropriate vaccination strategy, will deliver the best results (see box, bottom left), but the first thing you need to do is to assess your starting point by gauging the level of infection in your herd.
In dairy herds, an analysis of bulk tank antibody levels is a useful place to start, although this won’t give you all the answers. In beef herds, and to get a more accurate picture in dairy herds, you will need to test strategic cohort blood samples. This can be a complex process and is best planned with your vet.
Random sampling and testing may give an indication of the presence and prevalence of disease. But to monitor how a health plan is progressing, to identify BVD PI animals to be culled and to develop effective vaccination strategies, you will need to select carefully which animals you sample.
The Cattle Health Certification Standards (CHeCS) website – www.checs.co.uk – has more information on testing protocols.

What can be done to control them?

Biosecurity and risk assessment and management are absolutely vital, but vaccination is often a key tool.
Many vaccines lose efficacy if they are not stored and used correctly so the information given in the data sheet must be followed. If the vaccine needs to be kept cool before use, it should be collected from the dispensary in a cool box or an insulated container and then placed in a fridge as soon as you get home.
It is important to administer the vaccine via the correct route, usually either subcutaneously (under the skin) or intramuscularly. Frequently, an initial two-dose course of vaccine is required with an interval of four or six weeks between doses to stimulate full immunity. Booster doses of vaccine, often annually, but sometimes more frequently, are required to maintain immunity.
Proper healthcare records will ensure vaccination intervals and boosters are maintained.

Finding a strategy to ensure success

How you approach vaccination will depend on the overall aim for your herd’s health status.
Managing an endemic level of infection: Eradication of a disease may not be practical or cost-effective if, for example, you regularly buy in replacements or a high herd health status is not your key objective. Your vaccination strategy should aim to minimise the risk posed both to your established herd by replacement animals and to those replacements by endemic disease. All replacement animals should be tested to ensure no BVD PIs are added to the herd.
Improving herd health status: If eradicating an infectious disease is a viable option, greater attention will need to be paid to biosecurity and risk management, particularly when bringing in herd replacements. Vaccination may also play a key role and there may be a need to identify and then cull or manage infected or diseased animals appropriately.
Maintaining a disease-free herd: Biosecurity and risk management will be vital in keeping infection out of your herd. Running a closed herd is the ideal. If replacement animals must be purchased they should be sourced from herds with a proven health status, but infection can still be introduced through contact with stock on neighbouring farms.

Golden rules

  • Monitor – find out the health status of your herd now and assess how it is changing
  • Plan – discuss and agree a monitoring and possible vaccination strategy with your vet
  • Follow instructions – store and administer vaccines correctly
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