Respiratory tract infections account for almost 30%* of all calf deaths in Ireland. In very young calves (< 1month old) respiratory infections are the third most common cause of calf death* after scour and septicaemia. Over 1 month of age respiratory infections are by far the most common* cause of calf mortality.
Pneumonia can cause significant economic loss on a farm. Apart from the obvious loss associated with a dead animal, there are costs associated with loss of production and treatment. Cases that are not treated promptly can develop long term damage which permanently affects the lung function of that animal.
In young calves the main causes of respiratory disease are either viral or bacterial, or in most cases, a combination of both. The main viruses are RSV, IBR, Pi3, Coronavirus and BVD. The main bacterial causes are Pasteurella multocida, Mannheimia haemolyticaand, to a lesser extent, Haemophilus somnus.
In many cases viral infection reduces the natural bacterial defence mechanisms of the respiratory tract, facilitating bacterial infection which can be rapid and severe.
As with all calf illness, there are a number of mitigating factors which predispose young calves to the risk of pneumonia:
- Inadequate or poor quality colostrum
- Poor ventilation
- Shared airspace with older animals
Dystocia, or a difficult calving, can lead to a lack of oxygen in the calf and subsequent acidosis. This in turn affects the intake of colostrum, as well as reducing body temperature and the ability of the calf to withstand cold stress. All of this leaves a vulnerable calf at risk of respiratory disease.
Proper colostrum management is essential. Current recommendations state that a calf should receive three litres of milk within two hours of birth, from the first milking after calving (3-2-1)*. Giving three litres ensures that adequate antibodies are transferred if for any reason a cow’s colostrum is of poor quality. Passive transfer of antibodies to the calf within the first two hours is optimal.
The most recent data from regional veterinary laboratories shows that colostrum levels were inadequate in over 60% of submissions. Samples came from carcases for post mortem, or blood samples submitted by vets from clinically-ill animals. In other words, almost two thirds of calf submissions in our regional veterinary laboratories indicate a failure of colostrum management. Good calf immunity is a vital first step in disease prevention. For screening purposes, blood samples can be taken from a number of calves and submitted for a Zinc Sulphate Turbidity (ZST) test to monitor on-farm colostrum management.
Overcrowding and/or poor ventilation is a significant factor in the development of respiratory disease in calves. In practice I find that this becomes more prevalent as the calving season progresses, when more calves tend to be sharing the same airspace. Poor ventilation and increased humidity predisposes calves of all ages to respiratory disease.
An ‘All in – All out’ policy for calf groups can help avoid an outbreak in these situations. Bedding should be changed regularly so that calves have a dry lie at all times. Airflow through the calf shed should be adequate to accommodate the number of calves in that space, with fresh air from outside entering at above-calf level and adequate space in the roof to create a ‘stack-effect’.
Understanding the factors that predispose calves to respiratory infection is important, but implementing them can present challenges.
In the post-quota era a lot of dairy farms are increasing cow numbers. This in turn is leading to increased numbers of young calves. As a vet I have seen improved fertility and conception rates in recent years, which means more calves in one space at one time. An appropriate vaccination programme, in conjunction with managing the risks listed above will help in controlling respiratory disease.
In the face of an outbreak however, diagnosis of the causative pathogens and therefore identifying the correct vaccination protocol can prove difficult. Samples take time to process, and maternal antibodies from the dam can complicate isolation of pathogens. That said, proper testing is a prudent step in helping prevention of future outbreaks.
When an animal presents with pneumonia, prompt treatment with a suitable antibiotic and anti-inflammatory will increase the chances of a positive outcome. Whilst a virus is often the primary cause of respiratory disease, it can cripple the natural defence mechanism of the respiratory tract and bacteria quickly invade the compromised lung tissue. It is these bacteria which cause the most severe damage to the lungs. If treatment is delayed or inadequate, bacterial colonisation of the lungs leads to long term damage which affects productivity in the short and long term.
In-contact animals should also be monitored, and in some cases metaphylactic treatment may be warranted. This means treatment of all animals in a group, and may be advised when a number of animals are showing clinical signs.
Effective management of a pneumonia outbreak depends on early diagnosis, followed by prompt and appropriate treatment.
*AFBI/DAFM Veterinary Laboratories. All-island Animal Disease Surveillance Report 2013. Available at: http://www.afbini.gov.uk/all-island_animal_disease_surveillance_report_2013.pdf