Recently one of our farmers had a run of dying lambs that presented as pale, weak and dying within 24 hours of being seen. They had been drenched recently (2-3 weeks before) with Genesis Ultra. Since the presenting symptoms were similar to Barbers pole they were re-drenched with Exodus. This made no difference however and more animals were dying… so we performed post-mortem.
On post mortem the tissues were pink and there was no sign of redness of the gut, so Haemonchus contortus (barbers pole worm) was ruled out. However, the lungs were attached to the thorax wall, were hard, red and had pus in the lobes when cut into caused by acute viral pneumonia.
There are two forms of this disease- the chronic form that shows up at the works with pleurisy (inflammation of the lungs) and an acute form that can kill animals within 24 hours. Most cases are seen late summer to autumn.
Enzootic or viral pneumonia is caused by a combination of several viruses and bacteria, the virus (in NZ often a parainfluenza) usually causing the initial lung damage, allowing bacteria to colonize and damage the lungs. Two of the most common bacteria found are a mycoplasma (notoriously hard to treat) and another called Mannheimia Hemolytica.
- Loss of appetite
- Loss of condition
- Nasal discharge (white to yellow)
- Increased respiratory effort
- Sudden death
Some of these signs can look similar to other diseases so if you are unsure of your diagnosis please discuss with your vet.
Losses to farmers occur due to:
- • Deaths of animals- this can be significant during an outbreak
- Downgrading of carcasses due to pluritis and abscesses in the lungs.
- Decreased weight gain and wool production- a trial in New Zealand (2004) showed when over 20% of the lung surface area is affected, the weight gain of affected lambs is half that of unaffected lambs, doubling the time needed to reach slaughter weight.
In 2006 ovine pneumonia was blamed for losses of $53 million annually, so it is likely to be higher now.
Outbreaks occur often after periods of stress involving mustering and yarding, especially in dry, dusty conditions. Pneumonia is usually associated with a stress factor such as drenching, shearing, and transport- often this will come before an outbreak. High dust levels, hot weather, lack of shade, and pushing animals hard when mustering leads to respiratory distress. This, combined with crowding increases the rate of spread since it is transmitted sheep to sheep via contact and inhalation of the organisms. In this case we added a second drenching event which could have exacerbated the problem.
Antibiotics may help animals survive the acute form of disease but the lung damage is often so severe that by the time animals are seen that they are given too late. AgResearch are currently trying to develop a vaccine against the mycoplasma and Mannheimia bacteria – watch this space.