Morphological characterization and meiotic competence of oocytes collected from filly ovaries.

This study explores the effect of a filly’s age on the morphology of her ovaries and the oocytes they produce, as well as the oocytes’ ability to mature in vitro. The research reveals that a filly’s ovarian development and the quality of her oocytes are significantly influenced by her age, with older fillies producing oocytes that show similar competence to those of adult mares.

Study Methodology

• The research team examined the ovaries of slaughtered fillies, sorted into three age groups: less than 10 months old; roughly 1 year old; and approximately 1.5 years old. The ovaries of adult mares were used as a control group.
• The morphology of the collected ovaries and oocytes was evaluated. For the in-vitro maturation process, only oocytes with expanded (Ex) and compact (Cm) cumuli were used.

Major Findings

• The study recorded the presence of corpora lutea, indicators of ovulation or sexual maturity, in the ovaries of fillies of different age groups at varying rates. For instance, only 9.3% of fillies below ten months old had corpora lutea in their ovaries, compared to 80.9% in the mare group. This data suggests that about 37% of fillies reach puberty around the age of 12 months.
• There was no established relationship between the age of the filly and the morphology or appearance of the oocytes harvested. However, when compared to mares, less compact (Cm) oocytes were collected from filly ovaries.
• In the metaphase II stage, a critical point in the cell cycle, fewer oocytes from fillies (28.4-35.5%) reached this stage compared to oocytes of mares (50%). This difference was particularly significant in the group of fillies less than ten months old. However, in the expanded (Ex) groups, a similar proportion of oocytes of fillies and mares achieved the metaphase II stage.

Conclusion

• The study concluded that oocytes of fillies younger than 10 months displayed lower meiotic competence – their ability to complete cell division – than those of adult mares under the given culture conditions.
• Oocytes from older fillies presented meiotic competence similar to the oocytes of mares.
• Regardless of age, both filly and mare oocytes with expanded cumuli exhibited the same capacity for in-vitro maturation.