hCG promotes secondary ovulation and supplementary corpus luteum formation during early pregnancy in mares.
hCG administration in pregnant mares significantly increased the rate of secondary ovulation and shortened the time to ovulation compared to controls.
Where it sits
this study against the rest of the hcg (human chorionic gonadotropin) corpusSummary and findings
This study evaluated the effects of human chorionic gonadotropin (hCG) on ovulatory dynamics and serum progesterone concentrations in pregnant mares with dominant follicles. Thirty pregnant embryo-recipient mares were assigned to receive either 1500 IU hCG IV (n=17) or saline solution IV (n=13). The hCG group showed a higher ovulation rate and shorter intervals to secondary ovulation compared to the control group.
Abstract
This study evaluated whether the administration of human chorionic gonadotropin (hCG) during early pregnancy accelerates ovulatory dynamics and alters serum progesterone concentrations in mares with dominant follicles. Thirty pregnant embryo-recipient mares with follicles ≥35 mm during early gestation were randomly assigned to receive either 1500 IU hCG IV (hCG group; n = 17) or saline solution IV (control group; n = 13). Mares were monitored by serial ultrasonography to determine the ovulatory response and the interval to secondary ovulation. Serum progesterone concentrations were analyzed using two complementary approaches: a chronological post-treatment analysis and an analysis synchronized with ovulation timing. The proportion of mares that ovulated within 48 h after treatment was significantly higher in the hCG group than in the control group (82.4% vs. 0%; P < 0.0001). Likewise, the interval between treatment and secondary ovulation was shorter in hCG-treated mares (median: 1.7 days; IQR: 1.6-1.8) than in control mares (median: 22 days; IQR: 20-23; P < 0.0001). The interval between primary and secondary ovulation was also shorter in hCG-treated mares (median: 38 days; IQR: 34-43) than in control mares (median: 54 days; IQR: 51-60; P = 0.0008). The chronological post-treatment analysis revealed a significant group × time interaction for serum progesterone concentrations (P < 0.0001). When the analysis was synchronized with ovulation timing, progesterone concentrations increased similarly over time in both groups (time effect: P < 0.0001), with no significant group × time interaction (P = 0.28). These findings demonstrate that dominant follicles present during early pregnancy remain responsive to exogenous gonadotropic stimulation, allowing secondary ovulation and, consequently, the formation of supplementary corpora lutea. Although hCG administration altered the temporal pattern of serum progesterone concentrations by accelerating ovulatory events, post-ovulation progesterone dynamics remained equivalent between groups when the analysis was synchronized with ovulation timing.
Background
This study investigates the role of hCG in enhancing ovulatory responses during early pregnancy in mares, a topic of interest given the importance of ovulation timing for reproductive success. Prior research has indicated that gonadotropins can influence ovarian function, but the specific effects of hCG in this context were not well established. Understanding these dynamics could have implications for equine reproductive management.
Methods
Thirty pregnant embryo-recipient mares with dominant follicles ≥35 mm were randomly assigned to receive either 1500 IU hCG IV (n=17) or saline solution IV (n=13). The study monitored mares using serial ultrasonography to assess ovulatory responses and measured serum progesterone concentrations through two analytical approaches over time.
Results
The primary endpoint showed that 82.4% of mares in the hCG group ovulated within 48 h after treatment compared to 0% in the control group (P < 0.0001). Additionally, the median interval to secondary ovulation was significantly shorter in hCG-treated mares at 1.7 days (IQR: 1.6-1.8) compared to 22 days (IQR: 20-23) in controls (P < 0.0001). The study also reported a significant group × time interaction for serum progesterone concentrations (P < 0.0001).
Interpretation
These findings suggest that hCG administration can significantly enhance ovulatory responses in mares, aligning with previous literature on gonadotropic effects. However, while the statistical significance is clear, the clinical relevance of these findings may vary depending on individual mare responses and management practices. Limitations such as the small sample size and specific population may affect the broader applicability of the results.
Key findings
- 82.4% of mares in the hCG group ovulated within 48 h after treatment vs 0% in the control group, P < 0.0001.
- Median interval to secondary ovulation was 1.7 days (IQR: 1.6-1.8) in hCG-treated mares vs 22 days (IQR: 20-23) in controls, P < 0.0001.
- Median interval between primary and secondary ovulation was 38 days (IQR: 34-43) in hCG-treated mares vs 54 days (IQR: 51-60) in controls, P = 0.0008.
- Chronological post-treatment analysis showed significant group × time interaction for serum progesterone concentrations, P < 0.0001.
- No significant group × time interaction for progesterone concentrations when synchronized with ovulation timing, P = 0.28.
Limitations
- small sample size (n=30)
- specific to pregnant mares, limiting generalizability
- single-site study
- no long-term follow-up reported