The transition between preluteolysis and luteolysis in cattle

Area of Science:

• Reproductive Endocrinology
• Ovarian Physiology
• Bovine Reproduction

Background:

• Luteolysis, the regression of the corpus luteum, is crucial for the ovarian cycle.
• Understanding the precise transition from preluteolysis to luteolysis is key to reproductive health.
• Previous studies have not fully detailed the hormonal dynamics during this critical phase.

Purpose of the Study:

• To characterize the transition between preluteolysis and luteolysis in heifers.
• To investigate the temporal relationship between hormonal changes and luteolysis onset.
• To identify factors contributing to the duration of the transitional period.

Main Methods:

• Hourly blood sampling in seven heifers.
• Assay of progesterone (P4), 13,14-dihydro-15-keto-PGF2α (PGFM), and estradiol (E2).
• Designation of the transitional hour based on P4 oscillation peaks.

Main Results:

• The transitional period from the last PGFM pulse of preluteolysis to the first pulse of luteolysis was significantly prolonged (13.4 ± 1.3 h).
• Estradiol (E2) and PGFM concentrations were lower during the last preluteolytic PGFM pulse compared to the first luteolytic pulse.
• Progesterone (P4) rebounded at the transitional hour, with intervening P4 rebounds observed in some heifers.

Conclusions:

• The prolonged transitional period is influenced by increasing E2 concentrations and progesterone (P4) rebounds.
• The temporal association of luteolysis onset with a PGFM pulse may be obscured by these transitional events.
• This detailed characterization provides new insights into the complex hormonal regulation of the luteolytic transition.