Behavioral and hormonal pattern of repeat breeder cows around estrus

Area of Science:

• Veterinary Science
• Reproductive Endocrinology
• Animal Reproduction

Background:

• Repeat breeder (RB) cows represent a significant challenge in dairy production, often linked to suboptimal estrus expression and reproductive efficiency.
• Understanding the endocrine and behavioral differences between repeat breeder and normal cycling cows is crucial for improving fertility outcomes.

Purpose of the Study:

• To compare behavioral estrus intensity, endocrine patterns (estradiol, progesterone, LH), and ovulation timing in repeat breeder (RB) cows versus control (CTRL) cows.
• To investigate potential physiological factors contributing to reduced fertility in RB cows.

Main Methods:

• Synchronization of estrus cycles in 12 RB and 18 CTRL cows using the Ovsynch protocol followed by a prostaglandin injection.
• Monitoring of behavioral estrus, ovulation, and collection of plasma samples for hormone concentration analysis (estradiol, progesterone, LH) around estrus.

Main Results:

• Repeat breeder cows displayed more intense estrus behavior, despite similar estrus duration and preovulatory follicle size compared to control cows.
• A significantly shorter interval from prostaglandin injection to estrus onset (proestrus) was observed in RB cows (47.9 h vs. 56.1 h).
• RB cows exhibited numerically higher peak estradiol concentrations and significantly lower luteinizing hormone (LH) secretion prior to the LH surge (2.5 ng/ml vs. 4.6 ng/ml).

Conclusions:

• Repeat breeder cows exhibit heightened estrus intensity but also show a shortened proestrus and diminished LH concentrations preceding the LH peak.
• These endocrine alterations, particularly the subdued LH secretion, may negatively affect oocyte competence and subsequent embryonic development in repeat breeder cows.
• This study provides novel insights into the endocrine profiles associated with repeat breeding in cows, highlighting potential targets for fertility improvement.