Our objective was to develop alternatives to hormonal treatments to synchronize oestrus of gilts. Before puberty gilts exhibit a pre-puberty period during which boar exposure could induce and synchronize first ovulation. To develop practical non-invasive tools to identify this period and improve detection of the gilts to stimulate, we searched for salivary biomarkers of the pre-puberty period. Saliva samples were collected from 30 Large-White x Landrace crossbred gilts from 140 to 175 days of age. Gilts were exposed to a boar twice a day and subjected to oestrus detection from 150 to 175 days of age. Among the 30 gilts, 10 were detected in oestrus 4 to 7 days after introduction of the boar and were considered receptive to the boar effect, 14 were detected in oestrus more than 8 days after boar introduction, 6 did not show oestrus and were considered non-receptive. Saliva samples from 6 receptive and 6 non-receptive gilts were analysed for steroidome using GC-MS/MS and for metabolome using 1H-NMR spectroscopy. Four saliva samples per gilt were analysed: 26 days and 11 days before boar introduction (BI-26 and BI-11), the day of boar introduction (BI), 3 days later for receptive gilts (BI+3) or 7 days later for non-receptive gilts (BI+7). Data were analysed using repeated measures one-way ANOVA and orthogonal partial least squares discriminant analysis. Thirty steroids and 35 metabolites were detected in gilt saliva. The concentrations of 6 steroids were higher (P < 0.05) in receptive gilts than in non-receptive gilts at BI-26, BI-11 and BI. The concentration of 2 metabolites were lower (P < 0.05) in receptive gilts than in non-receptive gilts at BI-11. These candidates could be potential salivary biomarkers to detect receptive gilts. However, their low and variable concentrations in saliva require expensive analysis and limit their use in pig farms.