We have recently investigated several cases of sudden death in lambs that were diagnosed post mortem with pleuropneumonia, a very common problem typically occurring in late summer/autumn.
The economic impact of pneumonia is significant, not only due to lamb deaths but also with poor growth rates and downgrading of carcasses at slaughter. Heat stress has been identified as a major risk factor, specifically open-mouthed breathing and panting, which allows infective organisms to bypass the protective defenses in the nose. Other associated causes include dusty conditions, lack of shade, excessive dog use, high endophyte grasses and dehydration.
Shearing on the same day as weaning, with its increased stress and crowding also increases risk. However, set stocking lambs after weaning has been shown to have a protective effect. Fine wool breeds appear to be less susceptible, possibly due to increased heat tolerance.
Treatment is challenging however best results for prevention will occur from ensuring strong immune defenses, through good nutrition and disease control. Giving a dose of Livestock Survival Drench has also been reported to reduce the incidence of pneumonia.