Pneumonia is a common and potentially fatal disease, but risks of infection can be minimised through careful herd management. George Caldow, senior vet investigation officer with SAC, explains.

Pneumonia is a source of significant financial loss for both beef and dairy herds, mostly affecting youngstock, but occasionally posing a serious threat to adult cattle. A complex condition with a wide range of potential causes, it can often occur for no apparent single reason. By understanding the range of risk factors farmers can take steps to minimise them and reduce infection rates across the herd.

What is pneumonia?

Literally translated as inflammation of the lungs, pneumonia is a disease which affects the lungs of cattle, which can cause permanent damage and even death. There are two main types of pneumonia - viral and bacterial - although often the viral form leads on to a bacterial infection.

What causes it?

Typically, pneumonia is caused by a combination of factors, including stress on the animal, presence of viral diseases, housing conditions, and air quality. The most common viruses that cause pneumonia are respiratory syncytial virus (RSV) and parainfluenza type 3 (Pi3), which are present in all cattle herds, often without causing disease. The third virus is infectious bovine rhinotracheitis (IBR), which is less prevalent, but more virulent and can cause disease in cattle of any age. It often occurs when groups of cattle from several sources are mixed, or are housed in large herds, and can cause severe tracheitis even in adult cattle, leading to pneumonia and death.

The final virus to consider is bovine viral diarrhoea (BVD) which, although it does not cause damage to the lungs and airways, can impair the disease resistance of the group, leading to more severe infection.

With RSV and Pi3 always present, infection requires other triggers which compromise the animal's immunity and create an environment in which disease can thrive. Most commonly, pneumonia affects calves when they are weaned and housed for the first time, as they are under stress. Sheds with poor ventilation or dusty bedding are a particular risk, as are those which are under- or over-stocked, resulting in huddles of animals with poor immediate air flow. Mixing new groups of cattle will also introduce greater disease risk, impairing their immunity.

Calves living outdoors which are infected with RSV or Pi3 will generally suffer from a raised temperature for a few days before making a full recovery - although occasionally severe infections can prove fatal. But those infected indoors, where air quality is less good, will struggle to clear dust and inhaled organisms from their respiratory tract while under the burden of infection.

This then provides ideal conditions for bacteria to colonise the airways and multiply. The most common bacteria involved in pneumonia outbreaks are Mannheimia haemolytica, Pasturella moltocida, Histophilus somni and Mycoplasma bovis. These start to colonise the upper respiratory tract, and move down towards the lungs, triggering a case of pneumonia. Toxins produced by the bacteria, and by the body fighting infection, cause tissue damage which, if left untreated, can prove fatal.

What are the symptoms?

Cattle infected with RSV and Pi3 viruses will have a temperature of more than 39.5C, but often look well. The first sign of disease is usually loss of appetite, so farmers should take the temperature of any animal which is off its food. Some may develop nasal discharge and/or a cough, and are later likely to suffer from rapid respiration and laboured breathing.

It usually takes two to three days for initial infection to develop into bacterial colonisation and pneumonia, but stock can deteriorate extremely quickly from apparently healthy to seriously ill within a matter of hours. Where some calves present clinical signs, four to five times more in the same group are likely to be in the early stages of infection and presenting a high temperature.

How is it treated?

Once an animal is showing clinical signs of infection, it should be treated with antibiotics, along with any other animals showing a raised temperature. Usually, a broad spectrum antibiotic is used, but cases involving Mycoplasma bovis may be more difficult to treat due to a different sensitivity to antibiotics. Mycoplasma bovis is, therefore, the most likely strain to be associated with low grade, persistent pneumonia in calves.

What about relapses?

People often think that a relapse of pneumonia is due to antibiotic-resistant bacteria - but more commonly it is because treatment was not early enough to prevent tissue damage in the lungs.

Once tissue has died it cannot deliver the antibiotic, leaving pockets within the lungs which are not treated.

The bacteria in those areas, therefore, survive the treatment, and go on to recolonise the airways, resulting in a relapse. The animal will then need another course of treatment.

How can I prevent infection in the first place?

As with all diseases, prevention is better than cure, and there are many steps farmers can take to reduce the risk of pneumonia. To start with, try to keep youngstock as stable as possible - identify the risk periods, such as weaning and housing, and manage them as well as you can.

Check for nutritional deficiencies such as Vitamin E and selenium, which will weaken the animal's immune system. Young calves should all receive 10% of their bodyweight in good quality, first milked colostrum within 12 hours of life, to provide vital immune defence. Ensure housing is well ventilated but not draughty, with low-dust bedding, and stock to the right density to prevent huddling or overcrowding.

Minimising the level of disease threat is also important, particularly BVD, which is a common trigger for pneumonia as it depresses the immune system for several weeks. BVD control can be achieved through vaccinating the breeding cows to prevent young calves being affected from birth.

Where there is a risk of pneumonia youngstock should be vaccinated against RSV. Your vet can advise on whether your herd is at risk of Pi3 or IBR and vaccinate accordingly.

Different vaccines can be administered at different ages, so farmers should formulate their vaccination programme in discussion with their vet.

Golden rules

• Plan your control programme before the pneumonia season begins
• Take every effort to reduce the stressors and environmental factors that precipitate pneumonia
• Ask your vet to provide a written vaccination and treatment programme, and stick to it