Is There a Link between Vomeronasalitis and Aggression in Stable Social Groups of Female Pigs?

Abstract

The vomeronasal organ (VNO) is a bilateral chemosensory structure strongly involved in animal behaviour, thanks to its sensory epithelium (VNSE) that detects pheromones. Experimental VNO lesions can impair social, reproductive and maternal behaviour, while feline spontaneous vomeronasalitis has been associated with aggression. This study aimed to describe vomeronasalitis in farm pigs and explore its association with intraspecific behavioural alterations. Using 38 six-month-old pigs, the skin lesion score based on Welfare Quality® protocols was obtained during the fattening period. The seventy-six VNOs from these pigs were stained in haematoxylin-eosin for histological examinations. VNSE inflammation was classified considering its intensity. Skin lesions data were compared to vomeronasalitis. There were 34% of pigs that showed unilateral VNSE inflammation, while 66% were bilaterally affected. The mean ± SD number of skin lesions/animal was 4.4 ± 2.82, and 34% of pigs scored 1 (moderately wounded animals) at least once during the fattening period. Statistical analysis showed an association between bilateral vomeronasalitis and skin lesion score (p < 0.05) and between bilateral moderate vomeronasalitis and skin lesions number (p < 0.01). This is the first report linking vomeronasalitis to social life in farm animals. Considering the role of social life in animal welfare, our data opens a research field linking pathology to animal behaviour.

Inflammation interferes with chemoreception in pigs by altering the neuronal layout of the vomeronasal sensory epithelium

“…This study allowed us to better characterize vomeronasalitis in pigs and the modifications the condition induces in the VNO. Asproni et al ( 21 ) demonstrated that, when inflammation was present in a pig's VNSE, the animal was more susceptible to aggression by congeners. Our results showed that inflamed VNSE possesses a lower number of neurons responsible for chemoreception.…”

“…Asproni and colleagues revealed that the presence of VNO spontaneous inflammation (vomeronasalitis) was also associated with intraspecific aggression in cats (20). This link was recently confirmed in a stable social group of pigs, in which a strong correlation was found between the histological scores of VNO inflammation intensity and the number of skin lesions induced by social fighting (21).…”

“…This study included 76 VNOs sampled from 38 6-months-old female pigs ([Landrace × Large White] × Piétrain), corresponding to a population used for porcine VNO in a previous study ( 21 ) and to the common age of slaughtering, which allows having a representative image of what happens in a farm pig VNO during its productive cycle. They were maintained in the Institute of Agrifood Research and Technology (IRTA, Monells, Spain) facilities in slatted pens (5 × 2.7 m) with water and food ad libitum .…”

“…Each VNO was stained with hematoxylin and eosin (H&E, BioOptica, Milan, Italy) to classify VNSE inflammation intensity on a scale from 0 to 3 (0 = absence of any sign of inflammation: healthy epithelium, 1 = weak inflammation; 2 = moderate inflammation, 3 = strong inflammation), as previously reported ( 21 ).…”

“…In pigs, signs of aggression are linked to long-term social stress, which impacts their welfare and productivity ( 23 , 24 ). To date, the link between vomeronasalitis and behavior has been verified ( 21 ).…”