Characterization of immunoreactive IGF-I pattern during the peri-ovulatory period of the oestrous cycle of thoroughbred mares and its relation to other hormones.

The study aims to understand the pattern of ir-IGF-I, a type of hormone, and its relation with other hormones during the oestrous cycle in thoroughbred mares. It suggests that ir-IGF-I increases before ovulation along with oestrogen, indicating that these hormones could play a key role in the differentiation and maturation of ovarian follicles.

Objective and Method

• The study focuses on understanding the pattern of a hormone called ir-IGF-I during the oestrous cycle in thoroughbred mares, and its relation with other hormones. For this, nine non-pregnant, non-lactating thoroughbred mares were observed and bled daily to trace the changes in their ovaries and hormonal environment.

Follicular Waves

• During one interovulatory interval (IOI), two categories of follicular waves were observed – minor and major. The most significant follicle of the first wave (DF1) was first detected at D – 1.75 ± 0.47, with a growth rate of 2.78 ± 0.14mm/day. It reached its maximum diameter of 22.45 ± 0.75mm on day 6.65 ± 0.82.
• The second wave’s most significant follicle (DF2) had a growth rate of 2.15 ± 0.29 mm/day and reached a maximum diameter of 42.70 ± 2.63 mm on D 19.25 ± 0.43.

Interactions with Other Hormones

• The study showed that ir-IGF-I significantly increased before ovulation and demonstrated a similar pattern to oestrogen. The correlation between ir-IGF-I and oestrogen was strong (r = 0.84), thus possibly indicating the role of these hormones in follicular differentiation and maturation during the oestrous cycle of mares.
• As the study suggests, the primary source of circulating ir-IGF-I during the oestrous cycle is the ovarian follicles.

Conclusion

• The study concludes that ir-IGF-I is secreted during the oestrous phase, which runs parallel with the development of the future ovulatory dominant follicle. It postulates that this hormone may work in synergy with other hormones to help select and differentiate the dominant follicle during the oestrous cycle in mares.