Different chemical fractions of fetal fluids account for their attractiveness at parturition and their repulsiveness during late-gestation in the ewe

We have investigated whether the chemical components of fetal fluids (FFs), which elicit repulsion in late gestating ewes, are also those responsible for the attractiveness of fetal fluids at parturition. An aqueous fraction of FFs (A1), obtained after extraction with hexane, was tested for repulsion in late-pregnant ewes and for attraction at parturition. We also investigated if the repulsive and attractive characteristics of this A1 fraction were maintained after an additional extraction with dichloromethane (DCM, CH2Cl2) that produced two more fractions (aqueous/high polarity: A2 and dichloromethane/medium polarity: DCM). Thus, late-pregnant ewes were tested for repulsion of aqueous extracts of FFs (A1, A2 and DCM fractions) in a two-choice test of food preference, whereas parturient ewes were tested for attraction toward these same fractions in a two-choice test of licking warm spongy cloths. The A1 fraction was repulsive to late-pregnant ewes and attractive to parturient females. In contrast, neither the A2 nor the DCM fractions were repulsive to late-pregnant ewes, whereas both fractions were attractive to parturient ones. The discordance between the repulsive and attractive properties of the A2 and DCM fractions suggests that the attractiveness of FFs for parturient ewes and its repulsiveness for females outside the peripartum period depend on mixtures of substances that are at least partially different. Some compounds with high and medium polarity in the A2 and DCM fractions would act synergistically to generate the repulsiveness of FFs, whereas both high and medium polarity compounds can evoke attraction independently of each other.

► The repulsive/attractive character of fetal fluids was studied in pregnant and parturient ewes.
► Chemical partitioning of sheep fetal fluids was performed with hexane and DCM.
► Two-choice tests were used to assess the chemical fractions obtained.
► Compounds responsible for repulsion and attraction appear to be different.