Age affected: Weaners, growers/finishers.
Causes: Trauma; skin infections; ear biting; ergot poisoning.
Effects: Ear tips bloody, scabby, black or missing.
The major causes of ear necrosis are circulatory disturbance and trauma (damage). 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 the swine fevers, the viruses cause proliferation of the cells lining the blood vessels to 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 after ears have been caught in doors. Ear biting can result from investigation and biting of wounds from tags and clipping, but often results from nuzzling and biting following raised air speeds or poor air quality in the same way as tail biting. The lesions become colonised by bacteria and necrosis develops.
Sometimes the stimulus for ear biting is infection by exudative epidermitis (Staphylococcus hyicus in greasy pig disease) or other agents especially the spirochaete, Treponema pedis, which has been demonstrated in up to 60% of lesions.
Mode of transmission
The ear necrosis following circulatory disturbance due to infectious disease is a consequence of that disease and occurs in some cases of the condition. For the modes of transmission of salmonellosis and Classical Swine Fever, see the appropriate section. Ear necrosis due to the consumption of ergot is not transmissible, but can occur in successive batches of pigs 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 (S. hyicus, T. pedis) 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 pen furniture.
Ear necrosis which results from circulatory disturbance appears as if the ear tip is black down to a straight line. This black tip often dries up and falls off, leaving an ear ending in a straight line. The ear necrosis resulting from trauma such as ear biting is less easily seen, particularly when pigs are closely packed in groups. It is often on the outside bottom corner of the ear and may affect a relatively small area in the first place. Continued chewing by other pigs draws attention to the lesions and results in further damage and an increase in the area of blackened, swollen, inflamed and bleeding tissue. This damaged tissue may heal or continue as a sore, necrotic area until slaughter. Occasionally the ears are involved in generalised skin diseases such as exudtive epidermitis (greasy pig disease) or swine pox and the lesions themselves may become necrotic or form a focus for ear biting or further infection.
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 demonstration of antibody in 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 the swine fevers 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 distribution are and actively inflamed. A brief period of observation of the affected group usually allows the pig responsible to be identified.
The lesions of this condition are visible on superficial inspection and the animal survives. Their post-mortem appearance is the same as in life. Examination of the affected area may reveal systemic lesions of the causal disease and, in traumatic cases, oedema and thickening of the ear adjacent to the necrotic portion with swelling of the local lymph nodes.
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 exudative epidermitis, then the appropriate treatment may be given. Local dressing of wounds with wound powders may also improve healing and allow return to the group. 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 foregone, conditions for pigs should be improved, paying attention to air speeds and piglets may be weaned later to reduce the amount of nuzzling.