Minimising heat stress to prevent pneumonia in lambs
Associate Professor Maurice Alley, Institute of Veterinary Science, Massey University and Kathy Goodwin-Ray, PhD student.
Chronic non-progressive pneumonia (CNP) is a common disease of older lambs (5-10 months) although affected animals show few if any clinical signs. If more than 25% of the lung is affected then lambs may have reduced weight gain, exercise intolerance or have an occasional cough.
Pneumonia results from a complex interaction of infectious agents and the hosts defence mechanisms which are often compromised by environmental factors.
Pasturella organisms are the common infecting agents, but there many varieties and strains in New Zealand. Other viruses and bacteria are also known to cause pneumonia. Outbreaks can result in lamb deaths of 2-8% and often occur within a fortnight of a stress event like shearing. CNP is fattening lambs is also thought to cause production loss. Affected lambs may be on average 1.5kg lighter than controls without disease over a two month period. Pleural lesions resulting from pneumonia may also be a cause of downgrading of lamb carcases at meat processing works, even after lambs have recovered from the disease.
In the absence of an effective vaccine, it appears that the most positive management action sheep farmers can take to reduce losses of lambs on farms due to pneumonia is to minimise heat stress. Observation by farmers of lambs to prevent or reduce this, by unhurried mustering and droving, the provision of shade, and reducing access to grasses infected with toxic endophyte, are the most rational management procedures for reduction of pneumonia in heat-suspectible British-breed lambs, on the basis of our current knowledge of the risk factors of ovine pneumonia.
An indication of lambs are risk of pneumonia because of heat stress would be open-mouth panting. It is not an effort to inhale more air for oxygenisation as in exercising humans, rather it is the cooling mechanism by which sheep use respiratory evaporation to lower elevated body temperature.
Heat stress is common on sheep farms in New Zealand in spite of the relatively mild summer climate. Exercise-induced heat stress during mustering and droving is the major cause and the pyrexic effect of ergovaline in high-endophyte grasses intensifies the effect. Heat stress was also very common in lambs during transport through the tropics by sea, and it was the common experience of veterinarians involved in the live-sheep-for-slaughter trade to the Middle East that deaths from pneumonia in lambs began about 10-15 days into the voyage when ambient temperatures greater than 25 degrees C over the Indian Ocean caused temperatures in pens to rise.
MAF maintained records of daily temperature, percentage relative humidity and ventilation air flows, and mortality data, of the voyages in a live sheep export database. The sea transport of lambs was stopped in 1994 due to repeated ship-board epidemics of pneumonia.
Chronic non-progressive pneumonia (CNP) is a common disease of older lambs (5-10 months) although affected animals show few if any clinical signs. If more than 25% of the lung is affected then lambs may have reduced weight gain, exercise intolerance or have an occasional cough.
Pneumonia results from a complex interaction of infectious agents and the hosts defence mechanisms which are often compromised by environmental factors.
Pasturella organisms are the common infecting agents, but there many varieties and strains in New Zealand. Other viruses and bacteria are also known to cause pneumonia. Outbreaks can result in lamb deaths of 2-8% and often occur within a fortnight of a stress event like shearing. CNP is fattening lambs is also thought to cause production loss. Affected lambs may be on average 1.5kg lighter than controls without disease over a two month period. Pleural lesions resulting from pneumonia may also be a cause of downgrading of lamb carcases at meat processing works, even after lambs have recovered from the disease.
In the absence of an effective vaccine, it appears that the most positive management action sheep farmers can take to reduce losses of lambs on farms due to pneumonia is to minimise heat stress. Observation by farmers of lambs to prevent or reduce this, by unhurried mustering and droving, the provision of shade, and reducing access to grasses infected with toxic endophyte, are the most rational management procedures for reduction of pneumonia in heat-suspectible British-breed lambs, on the basis of our current knowledge of the risk factors of ovine pneumonia.
An indication of lambs are risk of pneumonia because of heat stress would be open-mouth panting. It is not an effort to inhale more air for oxygenisation as in exercising humans, rather it is the cooling mechanism by which sheep use respiratory evaporation to lower elevated body temperature.
Heat stress is common on sheep farms in New Zealand in spite of the relatively mild summer climate. Exercise-induced heat stress during mustering and droving is the major cause and the pyrexic effect of ergovaline in high-endophyte grasses intensifies the effect. Heat stress was also very common in lambs during transport through the tropics by sea, and it was the common experience of veterinarians involved in the live-sheep-for-slaughter trade to the Middle East that deaths from pneumonia in lambs began about 10-15 days into the voyage when ambient temperatures greater than 25 degrees C over the Indian Ocean caused temperatures in pens to rise.
MAF maintained records of daily temperature, percentage relative humidity and ventilation air flows, and mortality data, of the voyages in a live sheep export database. The sea transport of lambs was stopped in 1994 due to repeated ship-board epidemics of pneumonia.