Investigating Urocanic acid Concentration in Relation to Seasonal Subfertility in the Sow Model

Abstract

Reproductive success is critical to the continuity of supply by the Australian pork industry. Seasonal fluctuations limit the reproductive success of swine, causing a reduction in the potential maximum revenue of the Australian pork industry. Researchers at the University of Sydney identified a strong positive correlation between a variant in the gene for the enzyme urocanate hydratase (UROC1) and seasonal fertility differences between wild and domesticated canids. Urocanate hydratase acts on trans- urocanic acid (UCA) in the histidine deaminase pathway (HDP). Trans- UCA can be photoisomerized into cis- UCA by ultraviolet B (UVB) light. The HDP produces a reproductive neurotransmitter, glutamate, as an end product. Cis- UCA is thought to be involved in the activation of 5-HT2A serotonin receptors. This study aims to identify a relationship between the activity of the HDP as impacted by UROC1 expression and the circannual rhythm of commercially housed sows. The concentrations of trans- and cis- UCA were calculated from samples taken from the epithelium of 29 commercially housed sows from a University of Sydney owned farm in Camden, New South Wales, using cello tape. The results of this study show clearly that there are circannual rhythms in trans- and cis- UCA concentrations, but a clear connection with an oestrus status was unable to be observed. The concentrations of both isomers of urocanic acid peaked between December and March during a period when sow fertility is typically reduced. Across all reproductive statuses measured, pregnant sows displayed a significant positive relationship with trans- UCA (Pr(>|t|) = 0.0006), and lactating sows showed a significant positive relationship with cis- UCA (Pr(>|t|) = 0.0048). Given that trans- UCA is implicated in the HDP, and cis- UCA has been shown to activate serotonin 5-HT2A receptors, then presumably, trans- UCA induced HDP activity influences lactation and cis- UCA activated serotonin receptors influence pregnancy.