Eoin Ryan of UCD Vet Hospital discusses pneumonia which is inflammation of the lungs and respiratory airways and is one of the main causes of calf mortality in Ireland on an annual basis.

Pneumonia in cattle of all ages is a multifactorial disease entity, with infectious pathogens, management factors and environmental factors all contributing to its development.

In terms of infectious agents, calf and weanling pneumonia can be caused by viruses (IBR, RSV and PI3), bacteria (Mannhaemia haemolytica, Pasturella multocida, Mycoplasma bovis/dispar and Histophilus somnus), or parasites (lungworm).

In most cases with housed calves or weanlings, pneumonia usually occurs due to a mixed infection, i.e. an initial viral infection followed by secondary bacterial invasion.

Management factors play a huge role in determining the risk of pneumonia in calves and weanlings. Particular factors include colostrum management in neonatal calves (Figure 1); stressors such as the transport of calves/weanlings to and from the mart, and under-feeding of young calves (a large proportion of young dairy calves are under-fed in early life).

Environmental risk factors for pneumonia include poor ventilation in the calf housing; drafts at calf level; overcrowding in pens and mixing of animals of different age groups in the same airspace (a percentage of older animals will be carriers of respiratory viruses and will maintain these diseases in the herd by spreading them to younger animals sharing the same airspace).

Symptoms

The symptoms of pneumonia are well known and include increased rate and depth of respiration (heavy, loud breathing); high temperature, especially in the early stages (greater than 39.2°C/103.2°F); nasal discharge (clear in the early stages and thicker and coloured later in the course of the pneumonia), and coughing as pus and mucus builds up in the lungs and major airways.

There are some clinical symptoms that may lead one to suspect involvement by particular agents. IBR (Infectious Bovine Rhinotracheitis) is a virus that leads to disease of the upper airways and is associated with nasal and ocular (eye) discharge, a red or burnt appearance to the muzzle, and a high temperature early in the course of disease.

In contrast RSV (Respiratory Syncitial Virus) and PI3 (Parainfluenza 3) are pathogens that affect the lower airways, leading to severe respiratory disease (Figure 2) and high mortality in neonatal calves. The bacteria Mannhaemia haemolytica and Mycoplasma bovis are also primary pathogens of the lower airways and lungs. They also cause severe inflammation with extensive lung damage and frequently result in death or stunting due to irreversible lung damage.

Mycoplasma bovis may also lead to swollen joints. Mannhaemia is the most common secondary invader following initial viral infections. Histophilus somnus is usually a secondary invader following initial viral infection, although it can be a very significant primary pathogen in feedlot cattle.

Lungworm will obviously only be an issue in calves that have been grazing infected pasture for a period of time, and should always be considered among the causes of coughing in weanlings from late summer onwards.

Mycoplasma dispar can also cause coughing in weanlings but is not associated with high mortality rates.

Diagnosis

In almost all cases, the individual primary pathogen, or pathogens, causing the pneumonia cannot be identified based on clinical signs alone. Therefore, various diagnostic methods are available to your veterinary practitioner, including nasal swabs, lung washes (Figure 3), blood testing of calves over six months old, dung samples for lungworm larvae and post-mortem examination (Figure 4) of calves/weanlings that die of pneumonia.

Treatment

The response to treatment will depend on a number of factors, including early detection of cases; the animal's immune system (colostrum transfer); stressors such as overcrowding and poor ventilation, and the severity and type of infection.

One of the most common misunderstandings is that antibiotics do not combat viral infections in any way. Antibiotics are active against bacteria only and will certainly treat primary or secondary bacterial infections. However, there will be no response in the case of severe acute viral infections, resulting in relatively high mortality rates with RSV pneumonia in particular.

There are many very effective antibiotics available for the treatment of bacterial pneumonia, with differences in methods of administration and longevity of action. It is always advisable to consult with your vet on suitable treatment options and to obtain early veterinary intervention in the treatment/management of individual and group outbreaks of pneumonia.

As well as the use of antibiotics, anti-inflammatories play a crucial role in the treatment of individual cases of pneumonia. Remember that pneumonia is a process of inflammation of the lungs and respiratory tract, and inflammation results in changes and damage to the normal lung tissue.

Anti-inflammatories can be administered in all cases of pneumonia, both viral and bacterial, to reduce the extent of lung damage, reduce high temperatures and speed up recovery. General supportive care is also very important, including the provision of adequate nutrition and shelter/housing while the animals are sick.

Control/prevention

The prevention of calf disease is based on two main principles:

- Maximising immunity

- Minimising challenge

Maximising the immune status of the calf can be done by attending to a number of key areas. These include colostrum feeding; management/stockmanship; vaccination; reducing concurrent disease (e.g. BVD) and stress, and dry cow feeding (to ensure good quality colostrum and healthy strong calves at birth).

In terms of vaccination, there are effective vaccines available against IBR, RSV, PI3 and Mannhaemia haemolytica.

In general terms, vaccines can be divided into intranasal vaccines and injectable vaccines. The intranasal vaccines stimulate good immunity in a very short period of time (three to seven days) and are suitable for use in the face of an outbreak of pneumonia, even in very young calves (down to 10 days of age).

The immunity following intranasal vaccination, however, tends to be relatively short acting (three to four months).

In contrast, injectable vaccines may take three to four weeks (with a two-injection course) to stimulate maximum immunity, but it is longer lasting (six months in the case of IBR and up to 12 months for the other pathogens).

It is very important to remember that no vaccine gives 100% protection and, in the case of respiratory disease, if housing, ventilation and stocking rates are poor, then vaccine efficiency will be dramatically reduced. Therefore, attention should be paid to maintaining calf housing and reducing stressors to both calves and weanlings.

*This article was previously published in the Irish Farmers Journal on 22 October 2011 as part of a series on animal health.

Pneumonia in cattle a complex story

Calf and weanling pneumonia

This year, cattle are being housed as days remained mild while the cold bites in at night. With pneumonia emerging as an issue on many farms, we bring together key articles on this disease.