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

The vomeronasal organ plays a key role in intraspecific animal behavior since it is able to detect pheromones. Induced and spontaneous lesions of this structure have been previously associated with various social behavior alterations in animals. In cats, the inflammation of this organ, named vomeronasalitis, has been associated with the presence of aggression towards other cats. The aim of this study was to describe this pathology in farm pigs and to evaluate if it is associated with social alterations as described in cats. Our study showed that farm pigs can be affected by the inflammation of the vomeronasal organ and that the pigs with this alteration present an increased number of skin lesions induced by fights with other pigs. These results open an interesting perspective that links the alteration of this organ to the presence of aggressive behaviors in farm animals, which implicates an important issue in animal welfare. 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