Superovulatory response in lactating cows with different follicular dynamics

Area of Science:

• Reproductive Biology
• Veterinary Medicine
• Animal Science

Background:

• Superovulation is a key technique in assisted reproduction for cattle.
• The influence of pre-existing dominant follicles on superovulatory response in lactating cows remains unclear.
• Understanding follicular dynamics is crucial for optimizing superovulation protocols.

Purpose of the Study:

• To investigate the effect of a dominant follicle on superovulatory response in mid-late lactating cows.
• To analyze follicular growth dynamics, corpus luteum development, and embryo recovery rates.
• To assess if a dominant follicle negatively impacts superovulation outcomes.

Main Methods:

• Real-time B-mode ultrasonography (7.5 MHz rectal linear-array transducer) was used for daily ovarian scanning.
• Cows were classified into 'dominant' (>9 mm follicle, growing/stable <4 days) and 'non-dominant' (regressing/stable >4 days) groups.
• Ovarian structures and embryo recovery were monitored from pre-superovulation until day 7 post-estrus.

Main Results:

• The 'dominant' group showed significantly more 4-6 mm and 7-10 mm follicles on superovulation days 3 and 5.
• Higher numbers of preovulatory follicles (>4 mm) and day 7 corpora lutea (CL) were observed in the 'dominant' group.
• No significant differences were found in total or transferable embryo recovery rates between the groups.

Conclusions:

• The presence of a dominant follicle does not adversely affect superovulation in mid-late lactating cows.
• Current criteria for defining dominant and non-dominant follicles may require re-evaluation for lactating cows.
• Superovulatory response in lactating cows is likely influenced by multiple factors beyond dominant follicle status.