Wednesday, July 6, 2022

The silent killer

Pneumonia and pleurisy suck silently on production and have the potential to cut daily lamb growth rates in half.

Many farmers do not know that the “evidence of pleurisy” on lamb kill sheets is not accurately representing the number of lambs showing some degree of pneumonia.

In 2008, the cost to New Zealand’s sheep farmers was estimated at $53.2 million, although the actual cost could be much higher.

Recent work by AgResearch funded by Ovita, a partnership between Beef + Lamb New Zealand and AgResearch, has shown how widespread the problem is. Visual inspections of lungs have been undertaken on the processing chain at slaughter for the past three years and almost one-third of lamb mobs show signs of infection.

Rates of infection vary year on year. Dr Shannon Clarke, of AgResearch, gave the example of how one flock recorded a 55% rate of infection in 2010 but only 18% in 2009. She said it was possible the high rate of infection in 2010 was due to tougher environmental conditions and increased stress factors, as this was the year of the polar blast in Southland during September, where the lambs were from.

Environmental conditions and management had a huge impact, she said, but what was not yet known was what role genetics might play in predisposing lambs to infection. This is the centre of Clarke’s research.

“The heritability of pneumonia in sheep is unknown and so we are currently looking at the role genetics play.”

A reasonable degree of heritability could enable genomic selection of sires for this trait. This was the longer-term goal, Clarke said.

Trial work began in 2009 to identify lambs with pneumonia infection being processed as part of other Ovita-funded trials. The basis of research so far has focused on lung scoring for pneumonia and pleurisy. To date, 5500 lungs have been scored with 29% showing some degree of pneumonia infection but only 4% showing pleurisy.

There are two forms of sheep pneumonia in NZ. Chronic non-progressive pneumonia (CNP) occurs in lambs and hoggets between three and 10 months of age but is not normally visually obvious. It is associated with slower growth rates and is sometimes identifiable by a noticeable coughing in older lambs and hoggets, especially after exercise. Acute fibrinous pneumonia (AP) occurs in sheep of all ages and often leads quickly to death. Both forms can lead to pleurisy, which at autopsy is commonly described as when the lungs are stuck or joined to the ribcage.

The second stage of research begins this year and will focus on lamb growth analysis. 

  •  Pneumonia facts:
  •  Due to the large number of pneumonia-causing bacteria, vaccination development has not been economically successful.
  •  Managing stress factors is the best way to minimise infection. Factors include managing worm burdens, ensuring adequate nutrition, and not mustering lambs during the heat of the day, especially in dusty conditions. Allowing stock to stand after mustering before being yarded, and damping down sheepyards to minimise dust, are also recommended. Avoid additional stress factors at weaning such as excessive yarding and shearing.
  •  Mortality from AP can be as high as 8%. Clinical signs of AP include depression, weight loss, isolation from flock and fast breathing. Recovery is possible with antibiotics but lung capacity and weight gain can be permanently reduced.
  •  CNP is often referred to as “summer pneumonia” and is associated with high morbidity and reduced growth rates but low death rates. Clinical signs are often not obvious but can include chronic coughing and fast breathing, especially after exercise. Lung lesions can resolve after seven months and although lungs can be permanently shortened, full recovery is possible.
  •  Pleurisy normally develops as a result of large numbers of pneumonia bacteria extending from the lung surface to the chest cavity lining, resulting in fibrous adhesions between the lung and chest wall. Lesions remain, resulting in permanent lung damage.
  •  The Ministry for Primary Industries requires meat processors to record the incidence of pleurisy but not pneumonia.


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