Supplementation of equine early spring transitional follicles with luteinizing hormone stimulates follicle growth but does not restore steroidogenic activity.

The research investigates the effect of Luteinizing hormone (LH) supplementation on the growth and steroidogenic activity of horse follicles during the early spring transitional period. Although the LH treatment stimulated significant follicular growth, it did not lead to a restoration of their steroidogenic activity.

Research Methodology

• In this study, the researchers attempted to prove a hypothesis that supplementary LH in the period of early spring transition would stimulate the growth of dominant and steroidogenically active follicles.
• During the early transition period, mares were randomly divided into two groups, one that received a subovulatory LH dose, and the other that received saline as a control measure. This was done after the removal of follicles larger than 15 millimeters.
• The LH hormone was injected intravenously twice a day from when the largest post-ablation follicle was measured at 20 millimeters until a follicle size grew beyond 32 millimeters at which point an ovulatory dose of hCG (human Chorionic Gonadotropin) was introduced.
• A control experiment was also conducted on mares in June and July using saline treatment.

Study Findings

• The initial study findings revealed that the LH injections led to a significant increase in circulating levels of LH but had no influence on FSH (Follicle Stimulating Hormone).
• Administration of LH during the early transitional phase stimulated the growth of the dominant follicle, which attained similar diameters to the dominant follicles in the control group. However, LH had no effect on the size of the largest subordinate follicle or the number of follicles bigger than 10 millimeters during treatment.
• No significant difference was observed in the number of mares that ovulated in response to hCG in the transitional control, transitional LH, and the ovulatory control groups. However, all transitional mares returned to an anovulatory state post hCG-induced ovulation.
• Estradiol levels in the ovulatory control group increased during the experiment but stayed the same in transitional LH or control groups. Also, although progesterone levels increased after ovulation in transitional control and transitional LH groups, the values were significantly lower than that in the ovulatory control group post ovulation.

Conclusion

• Even though LH supplementation stimulated the growth of ovulatory-sized follicles, these follicles were deficient in development, which was demonstrated by their reduced steroidogenic activity.