Pneumonia and Pleurisy in Lambs

(principal researcher Kathy Goodwin of Epicentre, Massey University with collaboration of AgResearch, Agriculture NZ, Epicentre, Massey University and farmers from Southland, King Country and Northland)

The study objectives were to determine the effect of Chronic non progressive pneumonia (CPN) on:

1. lamb growth and quantify the cost to farmers
2. Identify on farm factors likely to have an influence on CPN
3. Features of the Pneumonia/Pleurisy spectrum
4. Develop methods for capturing reliable information in meat works

All the above, are necessary steps towards improved control programmes.

The trial was conducted in the King Country (6 farms), Northland (4 farms) and Southland (6 farms).
400 lambs per farms with 200 allocated to random and 200 to normal slaughter groups.
Pneumonia status was scored at slaughter.
Lambs weights were regularly taken.
Measures of management and environmental factors were recorded.

Although Pleurisy/Pneumonia are of limited importance from a public heath point of view it is an important disease to farmers due to the downgrading of carcasses and for the meat export industry because of the extra inspection cost and time involved to trim the carcass affected.

The disease can be split in three distinctive categories:

1. Acute fibrinous pneumonia, which is:
• rare on farms
• common on live lamb shipments
• occasionally death within 12 hours of onset of clinical signs
2. Chronic non progressive pneumonia (CPN), which is:
• common and affects most farms
• deaths are rare
• likely effect on lamb growth but difficult to measure
• linked to pleurisy
3. Pleurisy
• pleurisy is not an entity but part of a pneumonia/pleurisy complex as pleural adhesions are a likely consequence of any type of pneumonia
• producer cost because of downgraded carcass
• slaughter plant cost because of time involved to trim carcass and extra inspection cost.

Chronic non-progressive pneumonia (CPN) has multiple factors involved all rather poorly understood. There are a range of different micro organisms involved, which makes vaccine control unlikely. But lambs inherit maternal immunity and develop a natural resistance. Environmental factors such as management, nutrition and other diseases play a role.

CPN has a higher prevalence in late summer/autumn but occurs in all seasons in healthy lambs (3 to 10 months old).
CPN prevalence which commonly thought to be about 30% in autumn may actually reach up to 70% in some flocks.
CPN seems to affect lambs when the maternally derived effect is likely to be waning.

Micro-organisms associated with Lamb pneumonia:

• Bacteria: twelve different bacteria were recorded witch include several strains of Pasteurella, Staphylococcus and E. coli.

• Mycoplasmas: two different strains.
• Viruses: five different virus types.
• Unidentified cell-associated agent.

Possible risk factors:

There are many proposed but confirmatory evidence is lacking.

• stresses causing mouth panting allowing microorganisms to escape defence mechanisms of the nose
• heat humidity, dusty conditions
• opportunities for cross-infection are: yarding, shearing, drenching and shower or plunge dipping
• poor nutrition and or health lowering resistance to infection

Possible protective factors:

All very poorly understood.

• shearing
• vaccines
• Maternal immunity
• good nutrition and disease control
• low endophyte feed sources
• breed - Merino?

Summary conclusions:

• Regional differences in pneumonia prevalence increasing from Southland to the King Country to Northland.

• Variations in pneumonia prevalence between farms within each region is especially noticeable in Southland.

• Onset of pneumonia in lambs occurs earlier than thought with lesions evident at weaning drafts in each region.

• Northland lambs grazing chicory had a similar pneumonia prevalence but is in lower severity compared to those grazing ryegrass pastures.

• Vaccination against pneumonia is probably not cost effective unless there are high mortality rates.

• Restraints of the current study is not knowing how old pneumonic lesions are at slaughter of if lamb has had lesions that have resolved. This introduces bias to growth rate analysis.

• Further data analysis of current data will hopefully provide some insight into reasons for differences in disease levels between regions and farms.

• Further analysis may rule out some of the commonly held ideas about the causes of CPN.

• Lamb growth rate differs between the regions.

• Results show that pneumonia has a significant effect on growth rate.

• There is some way to go before we understand the costs of CPN and how best to control it.

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