Vaccination against Lawsonia intracellularis reduced tail-biting related behaviors in a commercial pig herd

BACKGROUND: Lawsonia intracellularis is the causative agent of proliferative enteropathy, a common enteric disease in pigs that compromises intestinal integrity and may influence behavior through inflammation and immune activation. Its potential link to tail biting, an abnormal behavior that causes stress, injury and pain, remains unexplored. This study evaluated the effect of vaccination against L. intracellularis on tail-biting related behaviors, tail lesions, active behaviors, and postures in pigs reared under commercial conditions. METHODS: The study compared two groups in a commercial herd naturally and subclinically infected with L. intracellularis: pigs vaccinated against L. intracellularis at 5 weeks of age and unvaccinated controls each comprising 21 pens observed from 11 to 28 weeks of age. Pigs had intact tails. L. intracellularis DNA in feces and specific antibodies in blood were detected by qPCR and ELISA, respectively. Tail-biting related behaviors (rear-end nosing and tail manipulation) were quantified by video analysis (n = 42 pens). Tail lesions were assessed weekly and individually for each pig (n = 516 pigs) using a standardized scoring system. Active behaviors (exploration, feeding, social interactions) and postures were recorded as additional behavioral measures. Haptoglobin (Hp), C-reactive protein (CRP), total esterase activity (TEA) and adenosine deaminase (ADA) were analyzed in blood or saliva. Mortality and average daily gain (ADG) were registered. Ethical welfare management measures (temporary space increase, tail spraying, and enrichment) were applied when recurrent or repeated bleeding from the tail was observed. RESULTS: L. intracellularis was detected between 15 weeks of age and 24 weeks of age. During this period, vaccinated pigs exhibited lower frequency of tail-biting related behaviors, whereas tail lesion scores did not differ between groups. Unvaccinated control pigs explored enrichment more frequently and were sporadically more active and restless while vaccinated pigs spent more time at the feeder. ADA concentrations were higher in vaccinated pigs, while Hp, CRP, TEA, mortality, and ADG did not differ (p > 0.05). CONCLUSIONS: Under natural subclinical Lawsonia intracellularis infection, vaccinated pigs demonstrated fewer tail-biting related behaviors and lower levels of active behaviors compared with unvaccinated controls. Although tail lesion rates were similar between groups, likely due to effective welfare management measures, the observed behavioral differences suggest that vaccination against L. intracellularis can enhance pig welfare even in the absence of clinical disease. Therefore, controlling subclinical enteric infections through vaccination may serve as an indirect yet practical complementary strategy to reduce tail-biting related behaviors on commercial pig farms.