Pneumonia and pleurisy in lambs

What are pneumonia and pleurisy?

Pneumonia is inflammation of the lungs while pleurisy refers to inflammation of the membranes that surround the lungs. These respiratory conditions can occur in all sheep; however, outbreaks are most common in weaners during summer.

What causes pneumonia?

Outbreaks of pneumonia are contributed to by environmental, animal and pathogen factors:

  • Environmental factors include dusty conditions, hot weather and excessive crowding.
  • Animal factors include inadequate nutrition, concurrent disease (e.g. internal parasites) and stress. These all impact the animal’s immune system making them more susceptible to pneumonia.
  • Pathogen factors refer to the bacteria and viruses that cause the disease. There are numerous pathogens that can be involved and can be either primary or secondary. Primary pathogens like Mycoplasma ovipneumoniae initiates a mild pneumonia with no or mild signs. This then makes the sheep more susceptible to a secondary bacterial infection which leads to severe disease. In some cases, parasitic infection from lung worm can also play a role.

In addition, poor drenching technique can lead to aspiration pneumonia.

What are the signs?

The severity of signs can vary greatly. Some sheep affected will not show any respiratory signs, only a reduction in weight gain. Others can develop nasal discharge, coughing, increased respiratory effort, lethargy and inappetence before progressing to death.

What is the cost?

National Sheep Health Monitoring Project (NSHMP) inspected sheep at the abattoir from over 1200 properties in Victoria in 2019–20. They found that greater than 70 per cent of properties inspected in Victoria had at least one sheep with evidence of pleurisy at the abattoir. Overall, they reported 2.7 per cent of sheep carcases inspected in Victoria were affected by pleurisy over the same period (NSHMP, 2020, page 30). However, there have been reports of single lines of lambs from farms having more than 15 per cent of carcases affected. This can have a significant economic impact, as pleurisy can lead to adhesions to the chest wall which means trimming of high-value cuts. Carcases with pleurisy can have 0.7–1.9 kg trimmed depending on if and how many ribs are affected (Lloyd, 2016). As a result, carcase trimming could lead to a loss to the producer of $5 to $15/lamb.

The economic cost on farm in Australia is not fully understood and likely variable between farms. Clinical cases of pneumonia lead to increases in mortality, increased treatment cost and reduced animal welfare. However, reductions in weight gain from mild cases are also likely to be important. New Zealand research has found that chronic non-progressive pneumonia results in significant reductions in weight gain. When 20 per cent or more of the lung surface area is affected a 72 g/day (or 53 per cent) reduction in weight gain was reported (Goodwin-Ray, 2006). Another New Zealand study showed that lambs with pleurisy on average took 22.8 days longer to reach slaughter weight (Hickford, 2014). As a result, the feed costs for lambs to reach market weight will be increased.

Prevention

Prevention should be focused on managing environmental and animal risk factors. Key points to consider include:

  • Handling/Transport
    • – Practise low-stress handling.
    • – Avoid handling/transporting sheep in hot dry conditions.
    • – Consider the impact of mixing purchased groups of lambs from different sources (stressful but also potentially exposes lambs to new pathogens).
  • Nutrition/Health
    • – Ensure nutrition and access to water is optimised.
    • – Ensure other major animal health issues such as intestinal worms are managed.
    • – Ensure suitable shade is available.
  • Dust management
    • – Hosing down dusty yards and laneways before moving stock.
    • – Consider impact of stocking rate on dust levels when containment feeding.
    • – Avoid dusty feeds.
  • Drenching technique
    • – Do not lift head above horizontal and do not drench in cradle.
  • Biosecurity
    • – New sheep introduced could be carriers of respiratory pathogens that are new to your flock.

Clinical cases of pneumonia can be treated with consultation from a private veterinarian. In Australia there are currently no registered vaccines for pneumonia in sheep available.

References

Animal Health Australia (2020) National Sheep Health Monitoring Project Annual Report 2019–20 (Accessed: 8 July 2021)

Goodwin-Ray, K.A. (2006) ‘Pneumonia and pleurisy in sheep: Studies of prevalence, risk factors, vaccine efficacy and economic impact’. PhD, Massey University, Palmerston North, New Zealand.

Hickford, J.G.H., Hodge, S., Bates, J.R. and Hogan, A.K. (2014) ‘Brief communication: analysis of the on-farm cost of ovine pleurisy.’ In Proceedings of the New Zealand Society of Animal Production (Vol. 74, pp. 62–64).

Lloyd, J (2016) An investigation of the potential link between arthritis and tail length in sheep. Meat and Livestock Australia

Page last updated: 16 Nov 2022