Induction of estrus and ovulation: why some mares respond and others do not.

The research study explores how and why certain mares respond to estrus and ovulation induction procedures, attributing the varied responses to physiological factors like follicle size, maturity, and stage of the estrus cycle.

Understanding Luteolysis and Ovulation Induction

• The research primarily addresses two common processes related to mare breeding management – induction of luteolysis and induction of ovulation. Luteolysis refers to the degradation of the corpus luteum, which produces progesterone necessary for maintaining pregnancy, while ovulation induction is the process of stimulating the ovary to release eggs for fertilisation.
• Researchers identified that both luteolysis and ovulation inductions are not always accurately timed due to varying physiological conditions.

Role of Prostaglandin and Follicle Size

• Prostaglandin F2alpha (PGF) or a PGF analogue in a diestrus mare – a mare in the phase between two periods of sexual heat or estrus – shows a documented average interval from treatment to the onset of estrus of around 3-4 days. However, ovulation typically occurs 8-10 days post treatment.
• The study emphasised the influential role of the ovulatory follicle’s diameter and status at the time of PGF treatment, allowing for a range of responses from 48 hours to 12 days for the onset of estrus and ovulation after treatment.

Ovulation Induction and Influential Factors

• Ovulation is commonly induced using human chorionic gonadotropin (hCG), recombinant LH (rLH), or the GnRH analogue Deslorelin, with typical ovulation occurring approximately 36 hours after treatment.
• The effectiveness of these treatments though can be impacted by a few key physiological factors such as the stage of the estrus cycle, follicle size, and maturity. This implies that the optimal response to inductions can significantly vary depending on the specific physiological state of the mare at the time of treatment.