Artiodactyl livestock species have a uniform vomeronasal system with a vomeronasal type 1 receptor (V1R) pathway

Artiodactyl livestock animals have a vomeronasal system that detects pheromones. Vomeronasal receptors comprise type 1 (V1R) coupled with G protein α-i2 (Gαi2) and type 2 (V2R) coupled with G protein α-o (Gαo). Laboratory rodents have two segregated V1R and V2R pathways that reach separately to the accessory olfactory bulb (AOB). In contrast, the AOBs of goats and sheep are entirely positive for Gαi2, indicating that they have only the V1R pathway. However, we detected a few V2R genes in the genome of cattle, goats, sheep and pigs by genome assembly. Thus, we immunohistochemically analyzed the AOBs of cattle and pigs to confirm which type of the vomeronasal system is present in artiodactyl livestock species. The glomerular layer of the AOB in cattle and pigs was entirely positive for anti-Gαi2 and weakly positive for anti-Gαo, as in the V1R uniform type of vomeronasal system in other mammal species. These findings indicated that artiodactyl livestock species have a uniform type of vomeronasal system composing the V1R pathway. Therefore, caution is advised when extrapolating knowledge of laboratory rodents with two vomeronasal pathways to livestock animals that have one.