Ear necrosis affects weaners, growers and finishers. The cause is normally trauma, skin infection, ear biting or ergot poisoning. The ear tips can get bloody, scabby or turn black and then cause the flesh to drop off.
The major causes of ear necrosis are circulatory disturbance and trauma caused by shaking their head near a hard object. Circulatory disturbance occurs during septicaemic infectious diseases. In erysipelas and salmonellosis, infected clots block the blood vessels to cause congestion of the ears, snout, tail and feet. The blood supply to the ear tips may be completely cut off and the congested part dies. In various viruses cause of proliferation of the cells lining the blood vessels cause blockage and the ears become necrotic.
When pigs eat ergot (a fungus found on rye and wheat), the active components constrict the blood vessels and cause ear necrosis. Necrosis of the ear tips occurs down to a straight line across each ear. Trauma (damage) usually results from ear biting but can occasionally occur from shaking their heads near hard objects, wall, door feed bin etc. Ear biting can result from investigation and biting of wounds from tags and clipping, but often results from nuzzling and biting. The lesions spreads by bacteria therefore necrosis develops.
Sometimes the stimulus for ear biting is infection, Staphylococcus hyicus in greasy pig disease, or other agents especially the spirochaete, Treponema pedis, which has been seen in approximately 60% of lesions.
Source of Transmission
Ear necrosis due to the consumption of ergot is not transmissible, but can occur in successive batches of pigs when fed on the same contaminated ration or grazing the same infected pasture.
When ear necrosis follows trauma due to ear biting or other causes, the same factors may affect successive batches. The bacteria infecting these lesions are transmitted from infected pigs after the initial damage has been caused, or are derived from the oral cavities of the aggressors. Infection is otherwise by direct contact with infected wounds on other pigs or by contact with contaminated housing/ark.
Ear necrosis is easily diagnosed by inspection. Necrotic ears caused by circulatory disturbance are usually obvious when the damaged, blackened tissue is still present, but become more so once the damaged tissue has fallen off to leave the appearance of an ear with the tip cut off. Closer inspection may be required to detect the necrotic lesions caused by ear biting, other trauma and localised skin infections. The cause of ear necrosis due to circulatory disturbance requires retrospective analysis. Salmonellosis is the most common cause at present in Western Europe, and examination of the affected animal may confirm this by the study of the blood or isolation of the organism from the pig or from others on the farm. The past presence of erysipelas may also be confirmed, but the possibility that swine fever may be involved should also be considered. Ergot poisoning requires a history of grazing contaminated ryegrass pasture or eating the fungus in contaminated grain. Lesions of ear necrosis caused by ear biting have a different symptom in that the ear is actively inflamed.
Treatment and prevention
There is no treatment for ear necrosis caused by circulatory disturbance, as the tissue is already dead. The necrotic tissue usually drops off cleanly and does not cause infection. Ear necrosis caused by trauma is different. The continual biting and the presence of inflammation mean that affected pigs may have to be separated from the group and reared alone. If this is done, then a course of injectable antimicrobial such as ampicillin can improve the ear and prevent necrosis from advancing.
Where the disease is due to lesions of treatable skin disease such as greasy pig, then the appropriate treatment may be given. Frequent dressing of wounds with wound powders may also improve healing followed by the reintroduction back to the herd. Prevention relies on treating or prevention of the predisposing disease in erysipelas or salmonellosis and correction of the ration in ergot poisoning. Ear biting can be prevented, but not consistently. It may be possible to coat the ear in an unpalatable material to discourage ear biting. Where the condition is occurring, then ear notching or tagging should be reduced or delayed.
- main picture courtesy pig333 Dr Rex Walters