Abstract
Background:
Progesterone, primarily produced by the corpus luteum, is essential for maintaining pregnancy in dogs by promoting endometrial receptivity and supporting fetal development. Hypoluteoidism, defined by inadequate progesterone production, significantly increases the risk of pregnancy loss and reproductive failure. This study evaluates the role of progesterone in canine pregnancy, the risks associated with hormonal deficiency, and the effectiveness of therapeutic intervention.

Aim:
This study emphasizes the role of progesterone supplementation combined with magnesium and tocopherol in supporting pregnancy maintenance and restoring hormonal homeostasis.

Methods:
Progesterone levels were monitored across the estrous cycle in French Bulldog bitches (n=20). The control group was divided into two subsets. At the first stage of the study, control group C1 (n=10) consisted of dogs in the anestrus phase. At the second stage, control group C2 (n=10) included dogs on days 18 to 22 of pregnancy. Animals in both control groups (C1 and C2) did not receive any pharmacological treatments throughout the experiment. The experimental group (dogs with luteal insufficiency, days 18 to 22 of pregnancy; n=10) exhibited significantly lower serum progesterone levels (9.90 ± 0.19 nmol/L) compared to the control group (55.60 ± 2.23 nmol/L, p<0.001). Serum progesterone levels were measured using the Immulite® system (Siemens Healthcare Diagnostics GmbH, Eschborn, Germany). The experimental group received treatment with exogenous progesterone (medroxyprogesterone acetate, MPA, Perlutex® 5 mg, Dechra, UK), administered orally at a dose of 0.1 mg/kg/day. The treatment was combined with tocopherol acetate (2.0 ml, 500 IU) for 21 days and MagiCalm® (1 tablet per 10–25 kg/day for 10–12 days). Blood sampling for hematological and hormonal analysis was conducted as follows: for the control group - on days 18–22 of gestation. In the experimental group (luteal insufficiency), samples were collected on the day treatment was initiated (Day 0; gestational days 18–22, prior to treatment initiation), and subsequently on treatment days 5 (23–27 days - 20.03±0.75 nmol/L; p < 0.001 ), 10 (33-37 days - 37.76±0.40 nmol/L; p < 0.001), 20 (43-47 days - 43.25±0.57 nmol/L; p < 0.001), and 30 (53-57 days - 33.37±0.87; p < 0.001).

Results:
It was found that during the anestrus phase (control group C1), the progesterone concentration was minimal (1.53 ± 0.07 nmol/L). Progesterone levels showed significant variation across different phases of the estrous cycle, measuring 4.56 ± 0.20 nmol/L (p < 0.001) in proestrus, 19.54 ± 0.17 nmol/L in estrus (p < 0.001), and peaking at 37.61 ± 1.96 nmol/L (p < 0.001) in metestrus. On gestational days 18–22, healthy bitches in control group C2 exhibited a plasma progesterone concentration of 55.60 ± 2.23 nmol/L, indicating normal luteal function. In contrast, the experimental group (bitches with luteal insufficiency on days 18–22 of gestation) demonstrated a significant decrease in progesterone levels (9.95 ± 0.27 nmol/L; p<0.001), accompanied by clinical signs such as restlessness, dark red vaginal discharge, and increased abdominal muscle tone. Throughout the treatment period, no critical clinical symptoms indicative of pregnancy loss were observed in animals with luteal deficiency. The clinical condition of all patients remained satisfactory. The pregnancies progressed with a dynamic normalization of plasma progesterone levels and culminated in normal, complication-free parturition.

Conclusion:
Progesterone therapy, when combined with tocopherol and magnesium, effectively addresses luteal insufficiency in dogs, improving implantation success rates and reducing pregnancy loss. This study highlights the importance of progesterone in canine reproduction and supports its supplementation as a viable treatment for hormonal imbalances.

Key words: Canine reproduction, Hormonal therapy, Hypoluteoidism, Luteal insufficiency, Progesterone