Porcine Ear Necrosis: Causes, Prevention & New Research Findings

Increasing attention is being paid to the welfare of pigs in recent years, as both consumers and producers seek higher standards in animal wellbeing. Among the welfare challenges in swine production, a condition known as Porcine Auricular Necrosis (PAN) continues to be a significant concern. This condition affects pigs in both the transition and growing phases and is characterized by lesions on the ear pinna. Lesions typically initiate as dry scabs on the tip or wounds at the base of the ear, but can evolve into wet, bleeding ulcers that can lead to partial loss of ear tissue. Originally described in 1984 as “porcine ear necrotic syndrome,” the term was used temporarily until its etiology and pathogenesis were clarified.

Understanding Porcine Auricular Necrosis

Although Porcine Auricular Necrosis (PAN) has a significant impact on pig welfare, its exact cause and pathophysiology have long remained unclear. Several potential factors have been suggested, including skin and systemic infections, deposition of immune complexes in the small veins of the ear, mycotoxins in feed, and ear biting. However, conclusive evidence has not been established over the years. The condition is generally considered a multifactorial one, likely influenced by a combination of factors:

• Biting
• Skin trauma
• High animal density
• Heat and/or high environmental humidity
• Incorrect diet composition

The complexity of PAN, and the limited existing research, has hindered a complete understanding of the condition. Even four decades after its initial official description, PAN remained partially unresolved. To deepen understanding, three field studies were conducted on farms in Belgium starting in 2019, forming the basis of a doctoral thesis. 3tres3 provides further background on the challenges of understanding this condition.

A Comprehensive Investigation

This research included an extensive study that encompassed:

• Assessment of PAN prevalence and lesion severity.
• Metagenomic analysis of pathogens present in lesions, blood, and skin.
• Antibody and antigen testing.
• Analysis of mycotoxins in feed, and blood.
• Histological examination of affected tissues.
• Environmental monitoring on farms.
• Evaluation of pig behavior (never before performed in relation to PAN).

This investigation, conducted on over 6,000 transition piglets (3–10 weeks of age) across five farms, revealed several key findings. The appearance, prevalence, and severity of ear lesions varied between farms and even between pens within the same shed. Initial lesions consisted of mild scabs, while wounds appeared later. Mild lesions did not affect piglet growth during the transition period. Lesion severity could differ between the left and right ears.

Identifying Potential Pathogens

Metagenomic analysis showed the most common bacteria present in lesions were Staphylococcus, Streptococcus, Mycoplasma hyopharyngis, Fusobacterium, Clostridium, and Prevotella. The viruses most frequently detected – astrovirus, picobirnavirus, rotavirus, and torovirus – were primarily enteric pathogens. PRRSV and PCV2 were absent or present at very low levels in blood. Mycotoxin levels in feed and blood were low and showed no correlation with PAN. Histological examination revealed primarily superficial alterations.

Behavioral assessment showed pigs frequently engaged in oral manipulation of their penmates’ ears, with variations in frequency over time. This behavior often occurred before visible lesions appeared, and piglets in pens with a high prevalence of PAN showed increased ear manipulation. Some farms also reported lesions on tails and flanks.

While numerous pathogens were detected in lesion scrapings, most were also present on intact ears, suggesting they are unlikely to play a role in the initial development of lesions. The histological findings, conversely, indicate that mechanical damage caused by oral manipulation, followed by secondary bacterial infection, is the most likely explanation for the clinical signs observed on farms. However, recent reports suggest the involvement of specific bacteria, particularly Fusobacterium necrophorum, in the etiology of PAN. Engormix highlights the economic impact of ear necrosis, increasing carcass condemnation rates.

The Role of Biting and Feeding Practices

Based on research, literature review, and field observations, initial lesions on the ear tip are most often due to biting, typically starting as a small scab. Lesions at the base of the ear, however, often occur while eating. When pigs lower their heads to the feeder, the base of the ear is exposed and can be bitten from behind. This type of biting can occur when space at the feeder is limited or when feed supply is insufficient. This aggression related to feeding may persist into the early growing phase if similar problems were present during the transition period. It is not uncommon for piglets imported to finishing farms in Poland to arrive with ear lesions, either recent or healed; these lesions usually resolve within approximately three weeks.

The utilize of antimicrobials may offer an apparent benefit, as the frequency of biting behavior often decreases naturally within 2–3 weeks, allowing lesions to dry. However, severe cases may require medication to prevent complications, such as pulmonary abscesses resulting from bacterial dissemination.

Preventing Porcine Auricular Necrosis

To reduce this negative behavior, the environment should be adapted to encourage animals to interact with their surroundings rather than with the ears of their penmates, although this can be challenging in modern intensive production conditions. Further research is needed to clarify the causes of biting, to elucidate the role of secondary bacterial skin infections, and to establish effective control and prevention strategies.

However, the results of short-term investigations should be interpreted with caution, as the prevalence of piglets with ear lesions is highly variable.

Key Findings and Implications

Behavioral observations indicated that oral manipulations often precede the appearance of visible lesions and occur more frequently in pens where pigs subsequently develop a greater number of ear lesions. Initial lesions on the ear tip are typically due to biting behavior, while lesions at the base of the ear appear more closely related to biting associated with feeding. Mild lesions generally do not affect productive performance, and biting behaviors often decrease spontaneously within weeks. Pathogens identified in lesion scrapings were also detected in clinically healthy ears, supporting the idea that bacteria act as secondary factors and not as primary causes.

In contrast, severe cases may require antimicrobial treatment to prevent complications. The term “ear necrosis” can be misleading, as these lesions are predominantly driven by behavioral factors and not by true necrotic processes.

The World Organisation for Animal Health (WOAH) emphasizes the importance of optimizing animal health and welfare in swine farming, encompassing the prevention, treatment, and control of diseases. WOAH provides comprehensive guidance on swine health management.