Urinary levels of oestradiol and pregnanediol glucuronides reflect the ovarian function in the domestic dog (Canis familiaris)

In many mammals, the reproductive cycle can be non-invasively monitored by measuring the concentrations of urinary steroid hormone metabolites. In domestic dogs, however, there is limited information available on the urinary excretion of oestrogens and progesterone. Oestradiol-3-glucuronide (E2G) and pregnanediol-3-glucuronide (PdG), the urinary metabolites of oestradiol-17β and progesterone, respectively, are commonly reported components of mammalian urine. In this study, we collected one to 28 daily urine samples of 43 female dogs after the onset of sanguineous vaginal discharge during 50 reproductive cycles. We developed an ELISA method for the measurement of urinary concentrations of E2G (nine cycles) and PdG (50 cycles). A linear mixed model was used to estimate the expected values and 95 % confidence intervals for the E2G and PdG concentrations. The expected urinary E2G was estimated to peak 6 days after the onset of sanguineous vaginal discharge and to decrease to one-third of the maximum concentration within a week. The estimates of the expected urinary PdG concentrations were low at the onset of sanguineous vaginal discharge and increased slowly thereafter, reaching maximum concentrations within three weeks. The similarity of the E2G and PdG models with existing literature suggested that urinary steroid metabolites could be a useful biomarker for detecting ovarian function in female dogs. Further detailed investigation is needed to enhance the suitability of E2G and PdG measurements in monitoring of oestrus. In summary, measurement of the urinary metabolites of steroid hormones is a promising non-invasive method for studying reproductive physiology in female dogs.