Farm Newsletter December 2020

Bovine Respiratory Disease

It is a little ironic that while the world is having to deal with a human respiratory disease, attempting policies that are both unworkable and ineffective, we are dealing with our own respiratory problems, very similar in their pathology and epidemiology, in the form of bovine respiratory disease, BRD, or calf pneumonia.

The stark difference is that with BRD, the young, rather than the elderly, are much more susceptible to severe disease, although this year we have also seen outbreaks in older fat cattle and even adult milking cows.

The impact of any infectious disease is a balance between the pathogens (the viruses, bacteria and mycoplasmas) and the host. Low doses of pathogens meeting resilient healthy calves will produce very mild disease, and then a strong immunity. This can be described as a managed exposure.

If the circumstances and situation are right for the pathogens, and wrong for the calf (the host), the balance goes the wrong way and disease occurs. High doses of the pathogens, which might occur in small airspaces with infected animals that are shedding large numbers of pathogens, will create high disease exposure for their fellow calves. Older cattle kept in the same sheds, or animals that have been previously badly affected and held back in younger groups can often be the source of such infections.

Some factors to consider:

Cold – adult cattle are heat generators – they don’t succumb to cold, but young calves are very susceptible. With a moderate air movement (a detectable draught) the critical temperature for a pre-weaned calf is just 90C. Once the air temperature falls below that, the calf has to use its own body reserves to keep warm. It gets chilled, and succumbs to any infection. Keep calves warm by avoiding draughts, using deep straw bedding and keep them dry.

Moisture load: moisture and humidity are the enemy of the calf and the friends of the pathogen. Cold damp air will stress the respiratory tract whatever the pathogenic load. A 200kg animal will consume about 25 litres of water each day, which has to go somewhere. Most will end up in the bedding. For 20 calves in a shed, that is 500 litres per day, or a tonne of water every 2 days. That water has to go somewhere: very little will evaporate in cold weather, and so it has to drain out, either through the floor or in to drains. Inevitably, most will stay in the bedding, creating the damp, cold, toxic bed on which those animals lie for at least 60% of their time.

Atmosphere and environment – Good straw is not readily available. Much of it is damp and dusty. The mould dusts in it (which will grow in straw of more than 22% moisture content) can be toxic. They reduce immunity, and destroy the natural defences of the upper respiratory tract. Living in mould dust is not good for your health. Mechanical straw bedding machines exacerbate the problem. This reduces the animals’ resilience to any infections that are around. They cough, inhale particles, and pathogens in to damaged airways and damaged lungs.

  • Keep calves warm, dry and comfortable: reduce the bedding area to create dry, deep, beds, and scrape put the moisture as often as possible.
  • Keep bedding dry and use the best straw possible. Avoid dust storms when bedding up.

Respiratory vaccinations – There is a plethora of BRD vaccines now available, with some working better than others. None are totally effective, and all depend on combining the vaccine with natural exposure and maintaining the innate resilience of the calf. Vaccines will not work in the face of high challenge and poor resilience.

The vaccines are also pathogen specific, and although multivalent vaccines (those that cover more than one pathogen) are available, there is no single vaccine that protects all animals against all BRD/pneumonia.

Before using vaccines, the risks of each pathogen need to be assessed, and the appropriate vaccine selected. The use varies between intranasal inoculations to injections, some of which require boosters; vaccination programmes can be complex and difficult to manage, but they do help when done properly. Ask us for advice for your particular circumstance.

Treatment for respiratory disease with non-steroidal injections such as Metacam reduces the clinical effects of the disease, and improves the chances of recovery. Antibiotics help, but do not cure the problem. The judgement that needs to be made is which to treat and which not. Metaphylaxis is the technique of treating animals before they are affected to prevent disease, and this can be beneficial in many outbreaks. This judgment is difficult, and balances cost, effectiveness, and time.

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