hCG promotes secondary ovulation and supplementary corpus luteum formation during early pregnancy in mares.
hCG significantly increased ovulation rates and reduced the time to secondary ovulation in mares during early pregnancy.
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 ovulation dynamics and serum progesterone concentrations in 30 pregnant embryo-recipient mares. Mares received either 1500 IU hCG IV (n=17) or saline IV (n=13). The hCG group showed a higher ovulation rate and shorter intervals to secondary ovulation compared to controls.
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 addresses the role of human chorionic gonadotropin (hCG) in enhancing ovulatory dynamics during early pregnancy in mares. Prior research indicated that exogenous gonadotropins could influence ovulation, but specific effects on progesterone levels and timing in pregnant mares were not well understood. This study aims to clarify these effects and their implications for reproductive management in equine practice.
Methods
The study design was a randomized controlled trial involving thirty pregnant embryo-recipient mares with dominant follicles ≥35 mm. Mares were assigned to receive either 1500 IU hCG IV (n=17) or saline solution IV (n=13). Monitoring included serial ultrasonography to assess ovulatory response and timing, with serum progesterone concentrations analyzed post-treatment and synchronized with ovulation.
Results
The primary endpoint showed that 82.4% of mares treated with hCG ovulated within 48 hours compared to 0% in the control group (P < 0.0001). The median interval to secondary ovulation was significantly shorter in the hCG group at 1.7 days (IQR: 1.6-1.8) versus 22 days (IQR: 20-23) in controls (P < 0.0001). Additionally, the interval between primary and secondary ovulation was shorter in the hCG group (median: 38 days, IQR: 34-43) compared to controls (median: 54 days, IQR: 51-60, P = 0.0008).
Interpretation
These findings suggest that hCG administration can significantly enhance ovulatory response in pregnant mares, which aligns with previous studies on gonadotropin effects. However, while the statistical significance is clear, the clinical implications may vary based on individual mare responses and management practices. The study's limitations, including a small sample size and lack of long-term follow-up, warrant caution in generalizing results to broader equine populations.
Key findings
- 82.4% of hCG-treated mares ovulated within 48 h after treatment vs 0% in control, P < 0.0001.
- Median interval to secondary ovulation was 1.7 days (IQR: 1.6-1.8) in hCG group vs 22 days (IQR: 20-23) in control, P < 0.0001.
- Median interval between primary and secondary ovulation was 38 days (IQR: 34-43) in hCG group vs 54 days (IQR: 51-60) in control, P = 0.0008.
Limitations
- small sample size (n=30)
- focused solely on mares, limiting generalizability
- no long-term follow-up assessed