Endocrine alterations associated with extended time interval between estrus and ovulation in high-yield dairy cows

Area of Science:

• Reproductive biology in domestic animals
• Endocrinology of estrus and ovulation
• Bovine fertility and artificial insemination

Background:

• Short gamete viability necessitates precise timing for artificial insemination (AI) in cattle.
• The estrus to ovulation (E-O) interval is a critical factor influencing AI success.
• Understanding hormonal changes during extended E-O intervals is key to improving bovine fertility.

Purpose of the Study:

• To investigate the association between extended estrus-to-ovulation (E-O) intervals and hormonal changes in high-yielding Holstein cows.
• To determine the relationship between estradiol, progesterone, and the preovulatory LH surge in cows with varying E-O intervals.
• To identify potential causes of reduced fertility linked to delayed ovulation.

Main Methods:

• Synchronized high-yielding Holstein cows (n=74) were monitored for estrual behavior and ovulation via ultrasound.
• Blood samples were collected pre- and post-estrus to measure hormone concentrations (estradiol, progesterone, LH).
• Cows were categorized by E-O interval: short (22-25h), normal (25-30h), long (31-35h), and very long (35-50h).

Main Results:

• Cows with very long E-O intervals exhibited reduced preovulatory progesterone and estradiol concentrations.
• The preovulatory LH surge was significantly lower in the very long E-O interval group compared to other groups.
• Postovulation progesterone levels were lower in cows with long and very long E-O intervals.
• Season, parity, milk yield, and body condition did not influence E-O intervals.

Conclusions:

• Reduced preovulatory estradiol and a diminished LH surge are associated with extended E-O intervals in Holstein cows.
• Delayed ovulation, potentially caused by these hormonal alterations, may lead to suboptimal oocyte maturation and reduced fertility.
• Lower progesterone levels before and after ovulation in cows with extended E-O intervals could further contribute to poor fertility outcomes.