Selected ovarian ultrasonographic characteristics during vernal transition are useful to estimate time of first ovulation of the year.

This research article investigates certain characteristics seen in the ovaries of mares during the vernal transition to predict the first ovulation of the year. The study determines no single feature is a definitive indicator of ovulation, but a combination of certain features can anticipate first ovulation in 44-67% of the mares studied.

Research Methodology and Procedures

• The study began by teasing mares with a stallion for oestrus detection starting from January 3.
• Mares were subjected to ultrasonographic examination to observe various characteristics in their ovaries during the vernal transition.
• The day of the first appearance of several different signs in the ovaries was recorded, including uterine oedema, follicular wall invagination, intrafollicular echogenicity, double contour of the follicle wall, increased granulosa thickness, follicular wall hyperechogenicity, and appearance of pear-shaped follicles. In addition, follicle diameter and count were registered.

Key Observations

• Seventy per cent of the mares had anovulatory oestrous periods averaging 4.6 ± 3.6 days, with an interoestroual interval of 12.5 ± 12.2 days.
• Uterine oedema, considered a sign of approaching ovulation, was seen in 77% of mares, typically 32.4 ± 25.6 days before ovulation.
• Follicular wall invagination was observed in 44.4% of the animals, approximately 24.5 ± 18.4 days before ovulation. Intrafollicular echogenicity was seen in all mares while a double contour of the follicle was seen in 77% of the animals. Both these characteristics appeared between 1-72 days before ovulation.
• Increased granulosa thickness and detection of pear-shaped follicles was noted 1-19 days and 3 or fewer days before the first ovulation respectively.

Conclusions

• The study concluded that no single characteristic could reliably predict the first ovulation of the year.
• However, a combination of increased granulosa thickness, formation of a pear-shaped follicle, and follicular wall hyperechogenicity, along with a reduction in the number of follicles > 15mm in diameter to < 3, could predict ovulation in 44-67% of the transitional mares, 1-19 days after these characteristics appeared.