New research identifies direct cause of porcine ear necrosis
Disease has never been reproduced before under controlled conditions.
By Matheus Costa
Porcine ear necrosis (PEN) - also known as ear‑tip necrosis or ear necrosis - has frustrated producers for decades. The condition is found worldwide, and is linked to welfare concerns, secondary infections and economic losses from reduced growth. But despite numerous theories and decades of research, the true cause of PEN has remained elusive.
A new controlled study provides evidence that Fusobacterium necrophorum can directly induce PEN‑like lesions in pigs, resolving a long‑standing debate about the cause of the disease.
This research marks an important step forward for producers and veterinarians seeking more targeted strategies to manage the condition.
Why this study mattersPEN was first scientifically described in 1976, although it was informally reported decades before that. It is a disease that has intrigued (and frustrated) producers and veterinarians for its relatively slow progression, yet significant sequelae (ear mutilation).
For years it has been associated with a long list of potential contributors - mycotoxins, Staphylococcus hyicus, Treponema pedis, PCV2, PRRS, Streptococcus, environmental stressors, air quality, humidity or pig behavior. However, the disease has never been reproduced under controlled conditions. In a previous attempt, the team had partially replicated the disease by exposing healthy pigs to lesions from sick pigs. This initial study helped shape the inoculation model, but was inconclusive regarding the cause of PEN. This new study shifts the narrative: PEN has an infectious cause (Fusobacterium necrophorum, Figure 1), and it can be reliably reproduced under controlled conditions similarly to what producers have often observed during outbreaks.
How the study workedResearchers ran three controlled, single‑blinded animal trials where the treatment each animal received was unknown to those monitoring the pigs, reducing bias:
Trial 1: Staphylococcus hyicus
Trials 2 & 3: Fusobacterium necrophorum
Every trial followed a similar design: Twelve 5‑week‑old pigs per trial were used, sourced from a high‑health commercial herd with no prior history of PEN. Pigs were inoculated intradermally, into the tip of one ear while the opposite ear received sham inoculation.
The goal of the intradermal inoculation was to mimic ear biting. Sentinels were also included to ensure PEN did not spontaneously develop.
Staphylococcus hyicus did not cause lesionsIn Trial 1, no PEN‑like lesions occurred in any pigs inoculated with S. hyicus.This helps eliminate one of the commonly suspected agents.
Fusobacterium necrophorum reproduced classic ear necrosis (Figure 2)In Trials 2 and 3:
4 out of 10 pigs in Trial 2 developed lesions identical to PEN.
7 out of 9 pigs in Trial 3 developed PEN‑like lesions.
Lesions ranged from skin reddening to scab formation, progressing to full‑thickness necrosis and sloughing of ear tissue, the exact presentation seen in field cases.
Necrosis took about 4–6 days to develop.
This is the first controlled reproduction of PEN, and it required only a single bacterium.
F. necrophorum was isolated from the inoculated ears of affected pigs in both trials. In some animals, the opposite, uninoculated ear also developed lesions, suggesting possible spread via blood.
Microscopic lesions matched field outbreaksTissue samples from necrotic ears showed:
“Repair” tissue
Loss of skin
Thick crusting with and inflammation
Filamentous structures consistent with Fusobacterium spp.
Implications for the swine industry
1. Identifying a causative agent opens doors to targeted preventionProducers and veterinarians can now focus on management strategies that reduce F. necrophorum exposure or entry via skin trauma - similar to how we approach foot rot in cattle.
2. Ear trauma + bacterial exposure = highest riskThe study supports a model where ear chewing, abrasions or environmental injuries create the entry point needed for infection. It is important to know that F. bacterium is shed in feces and can be found in the saliva of healthy pigs. It remains unclear if any F. necrophorum is capable of causing disease, or if specific types are more aggressive than others (similarly to E. coli or Streptococcus suis)
3. PEN should be viewed as an infectious, not purely environmental, conditionEnvironmental stressors may still contribute, but they are not the sole cause. The bacterial agent is a required factor.
4. Biosecurity adjustments may helpBecause F. necrophorum is common in manure and the environment, farms managing PEN may consider:
Reducing stocking density
Strengthening sanitation around feeders/waterers
Minimizing opportunities for ear trauma, including the identification of bully pigs and removal from pens
5. A pathway toward vaccine development or therapeuticsWith a definitive agent identified, tools targeting Fusobacterium could become viable future options.
Take home messageThis study represents a major breakthrough: Strong evidence suggests that F. necrophorum is the primary cause of porcine ear (tip) necrosis.
The ability to reproduce PEN in a controlled research setting provides clarity long sought by producers, veterinarians and industry advisors.
By focusing on managing bacterial exposure and preventing ear trauma, farms may finally be able to reduce the incidence and severity of this welfare‑related condition.
This work was funded by the Saskatchewan Agriculture Ministry (Agriculture Development Fund), and Result Drive Agriculture Research.
Costa is an associate professor in large animal clinical sciences in the Western College of Veterinary Medicine at University of Saskatchewan, and an adjunct professor in population health sciences in the Faculty of Veterinary Medicine at Utrecht University.
