Necrotic ear syndrome in swine occurs worldwide and results in progressive loss of pinnal tissue in nursery and early grower pigs. Although it does not affect production, necrotic ear syndrome is an animal welfare concern because of its painful nature. Clinical signs begin with erythema and edema and progress to necrosis and loss of tissue. Diagnosis is based on clinical appearance. Management and prevention are primarily aimed at husbandry changes to avoid trauma.
Pigs with necrotic ear syndrome have unilateral or bilateral necrosis of the pinnae, are unthrifty, and occasionally develop septic arthritis or die from secondary bacterial septicemia. The condition occurs sporadically in weaned and growing pigs under all management systems, particularly when challenged with endemic diseases that can influence feed intake.
Etiology and Pathogenesis of Necrotic Ear Syndrome in Swine
The causes of necrotic ear syndrome have not been determined conclusively. Three causes are currently hypothesized: 1) damage of the epidermis due to staphylococcal exfoliative toxins; 2) occlusion of small blood vessels; and 3) ear biting with subsequent beta-hemolytic streptococcal infection.
Histological and microbiological findings suggest that the aggressive, erosive-to-ulcerative lesion is due to secondary bacterial infection. In the early phases of the disease, large numbers of Staphylococcus hyicus and low to moderate numbers of beta-hemolytic streptococci are found in the surface exudate. Later, during the ulcerative and necrotic stage, large numbers of beta-hemolytic streptococci are found deep in the lesion.
It is hypothesized that S hyicus colonizes the traumatized tissue, preparing the way for highly invasive beta-hemolytic streptococci that induce the changes that lead to ulceration and necrosis. Efforts to reproduce the disease by experimental inoculation of the two organisms have been unsuccessful.
Spirochetes have also been found in skin samples from ear lesions using silver stain, and Treponema spp have been amplified and sequenced from DNA prepared from ear lesion scrapings and broth cultures. However, the primary role of spirochetes in causing ear necrosis in pigs is unknown at this time. Moreover, it is thought that porcine circovirus type 2 (PCV2) infection might contribute to ear necrosis, because controlling PCV2 infection through systematic vaccination has reportedly decreased the frequency of ear necrosis on farms (1).
Clinical Findings, Lesions, and Diagnosis of Necrotic Ear Syndrome in Swine
The nature and extent of clinical signs of necrotic ear syndrome depend on the severity of the local lesion and the (less common) development of secondary bacterial septicemia. Thus, a spectrum of clinical signs may be observed, including the following:
unthriftiness
anorexia
fever
septic arthritis
collapse
death
Mild lesions consist of superficial scratches covered with thin, dry, brown crusts. Mild edema or erythema might be present near the scratches. In more severe cases, thick, brown, moist crusts cover deep ulcers.
In the most severe cases, there is extensive necrosis. Lesions evolve from mild, superficial dermatitis to severe, deep inflammation with exudation, ulceration, thrombosis, and necrosis.
In mild cases, resolution occurs with no loss of ear tissue; in severe cases, the margins, tips, or even the entire pinna can be lost.
Diagnosis of necrotic ear syndrome in swine is based on the appearance of the affected ears.
Management and Control of Necrotic Ear Syndrome in Swine
Ear biting is strongly associated with the incidence of necrotic ear syndrome in pigs. Avoiding trauma to the ear and controlling superficial lesions with topical antiseptics, such as iodine, can help stop progression.
Proper management practices, such as appropriate ventilation, location and functioning of waterers, pen design, group size, and mixing, should be followed.
Levels of lysine and other amino acids in the diet should be checked and corrected if insufficient, as these dietary deficiencies are known to be associated with increased ear biting (2). (See also Preventive Health Care and Husbandry of Pigs.)
Proper immunization against porcine circovirus type 2 is important for decreasing the frequency of ear necrosis.
Key Points
Lesions of necrotic ear syndrome in swine can begin as superficial dermatitis at sites of ear trauma that typically result from ear biting among piglets at weaning.
Early lesions (vesicles, bullae, erosions) are superficial and are often associated with Staphylococcus hyicus infections.
Superficial lesions can progress to deeper lesions (ulceration and necrosis) and are often associated with beta-hemolytic streptococci.
Deep lesions can progress to sloughing of the pinnae and systemic involvement.
Vaccination for porcine circovirus type 2 has been associated with decreased incidence of necrotic ear syndrome.
For More Information
Malik M, Chiers K, Boyen F, Croubels S, Maes D. Porcine ear necrosis. Vet J. 2021;271:105655.
Boulbria G, Nicolazo T, Teixeira-Costa C, et al. Porcine ear necrosis is associated with social behaviors in weaned piglets. BMC Vet Res. 2024;20(1):118.
What’s wrong with my pigs? Ear necrosis. The Pig Site.
References
Pejsak Z, Markowska-Daniel I, Pomorska-Mól M, Porowski M, Kołacz R. Ear necrosis reduction in pigs after vaccination against PCV2. Res Vet Sci. 2011;91(1):125-128. doi:10.1016/j.rvsc.2010.08.015
Meer YV, Gerrits WJJ, Jansman AJM, Kemp B, Bolhuis JE. A link between damaging behaviour in pigs, sanitary conditions, and dietary protein and amino acid supply. PLoS One. 2017;12(5):e0174688. doi: 10.1371/journal.pone.0174688
