Repeated use of a GnRH analogue deslorelin (Ovuplant) for hastening ovulation in the transitional mare.

This study explores the effects of using a Gonadotropin-releasing hormone (GnRH) analogue, deslorelin (Ovuplant), to speed up ovulation in transitional mares. The findings reveal that this method is more effective when mares enter into their transitional period and can facilitate increased ovulation rates.

Background

• Mares in winter anoestrous undergo a reduction in GnRH synthesis and storage in the hypothalamus. This, coupled with a decrease in luteinising hormone (LH) in the anterior pituitary, affects their reproductive cycle.
• The induction of ovulation in these mares during deep winter anoestrous is often discouraged on commercial breeding farms due to poor responses to GnRH or analogues and the failure of the mare to maintain the corpus luteum (CL) that results from induced ovulations.
• Researchers have previously suggested that continuous administration of GnRH agonists may be able to induce ovulation in mares during seasonal anoestrus. However, inconsistencies in the rate of mares ovulating and lack of reproducibility made this approach unfit as a dependable method for controlling breeding activity in commercial broodmares.

Methodology and Findings

• Pulsatile administration of GnRH has shown better results compared to constant infusion.
• Further success was observed when mares entered the transitional period, a phase where photoperiod, nutrition, and warmth combined to increase GnRH synthesis and storage.
• Transitional progression can be tracked hormonally or by examining the follicular population through ultrasonography.
• The predicted response of early or mid-transitional mares to regular infusion of GnRH or analogues resulted in a 5&75% ovulation rate.
• Most mares maintained the CL and, later in the transition, they responded more predictably.

Role of Deslorelin (Ovuplant)

• The GnRH analogue deslorelin (Ovuplant) has demonstrated efficacy in increasing LH and triggering quicker ovulation in cycling mares.
• The LH profiles in cycling mares indicated a dosage-dependent response with peak effect between 12-24 hours and a duration of 3-4 days after implantation with deslorelin.