[Sonographical visibility of the corpus luteum in dairy cows]

The study aimed to evaluate the day from which a corpus haemorrhagicum in the dairy cow after spontaneous or induced ovulation can be visualized using a mobile ultrasound device.

During three uninfluenced control cycles and three cycles in which six cows received a simultaneous treatment with GnRH and PGF2a, either on day 7, 14 or 17 post ovulation, the ovaries were scanned sonographically. In every control cycle a daily ultrasound examination was conducted starting from the 18th day of a cycle, in the treatment cycles beginning from the day of the hormonal treatment. Thus the formation of a new corpus luteum was followed sonographically from the day of ovulation onwards. Concentrations of progesterone were determined on day 1 of any cycle, on the day of hormonal treatment and on the 5 days following the treatment to support the sonographical results through endocrine values.

A corpus luteum was visible in 100% of the cases on day 5 of the cycle, regardless of whether it had been a spontaneous or induced ovulation. In the treatment cycles, a sonographically visible luteolysis induced by the hormonal treatment began between 1.3 and 1.8 days after the hormone injection and lasted on average 3.7 days. The day of the cycle on which hormonal treatment was performed had no influence on the occurrence of luteolysis. A central fluid-filled cavity was visible in 33% of the corpora lutea, becoming smaller during luteolysis and disappearing before luteolysis was completed.

A corpus luteum is sonographically visible on day 5 after ovulation. Ultrasound examinations can be used to confirm induced luteolysis. The formation of a new corpus luteum can be visualised to confirm the success of an induced ovulation.