Evaluation of steroid concentrations in the saliva of pre-pubertal gilts for the identification of biomarkers of the pubertal stage of maturity

Estrus synchronization is important for optimal management of gilt reproduction in farms. Synthetic progestogens are used for this purpose, but there is growing demand for non-hormonal alternatives. Before puberty, gilts exhibit a “waiting period”, related to ovarian development and gonadotrophin secretions, during which external stimulation, such as boar exposure, could induce and synchronize first ovulation. Practical non-invasive tools for identification of this period in farms are lacking. During this period, urinary estrone levels are high, but urine sampling is difficult in group-housed females. Our aim was to search for steroidal biomarkers of this “waiting period” from immature to pubertal gilts through saliva monitoring. Six 144-to 147-day-old Large White gilts were subjected to ultrasound puberty diagnosis 3 times a week until first ovulation. Urine and saliva samples were collected at the same frequency for estrone assay and steroidome analysis respectively. Data were analyzed using the R software (nonparametric permutation test). Urinary estrone concentration significantly increased 2 weeks before puberty (detected at 182–192 days). Steroidome analysis quantified 28 steroids in saliva. Significant variations were detected within 2 weeks before puberty for dehydroepiandrosterone (decrease) and estradiol-17b (increase). These steroids could be biomarkers of the “waiting period”. These results confirm that non-invasive salivary sampling could allow the identification of the physiological status of the gilts and presumably the optimal time for application of the boar effect