Hormonal changes in the peripartum period of the bitch

A blood sample was collected for routine progesterone assay, and serum was stored at −20°C. The day of parturition and the number of delivered puppies were registered. Concentrations of corticosteroids, androgens, progestogens, estrogens, for a total number of 17 different hormones, were measured using ultra-performance supercritical fluid chromatography–tandem mass spectrometry. Data were analyzed using a repeated measure, mixed-model approach, taking into account day (from day −4 to day +2 from parturition), age, parity (primiparous vs pluriparous), number of delivered puppies (<4 vs 4–8 vs > 8), and interactions between factors.

Day related to parturition significantly affected the concentration of progesterone (P < 0.001), testosterone (P < 0.001), 17α-hydroxyprogesterone (P = 0.0002), and cortisone (P = 0.006). Estrogen concentration did not show any significant variation over time. Testosterone and androstenedione showed an abrupt decline on the day of parturition. The concentration of all glucocorticoids increased the day before parturition. Age or parity was not significantly associated with any of the steroids. Litter size significantly affected concentrations of aldosterone (P = 0.02) and etiocholanolone (P = 0.01). Aldosterone concentrations were higher in litters with 4 to 8 pups than in litters with more than 8 pups (P = 0.02).

None of the steroids measured in our study, with the already known exception of progesterone, shows potential to be clinically useful in predicting the onset of parturition in the bitch.