Acceleration and Timing of Fertile Ovulation in Cyclic Mares with a Deslorelin Implant

Abstract

In a blinded trial, the effectiveness and safety of 2.2 mg of the GnRH analog deslorelin acetate, administered in a short–term implant (STI) to normally cycling mares in estrus with a dominant ovarian follicle of 30 mm in diameter or larger, were evaluated, using a placebo implant as a negative control. A total of 39 mares received treatments at admittance with pre–randomized implants containing either 2.2 mg or 0 mg deslorelin. Mares were teased daily and examined rectally with ultrasound at 24 h intervals to determine time to Ovulation and duration of estrus. The number of breedings and the pregnancy rate at 18 (±3) and 38 (±3) days were recorded, as were systemic side effects and local reactions at the implantation sites. Pregnancies resulting from breedings during the treatment estrus and/or from breedings during the next estrus were followed and the early and late pregnancy loss rate, the number of pregnancies going to term and of live–born foals was recorded.

Mean follicle diameter at treatment was not significantly different between the deslorelin and placebo treatment group with 41.6 mm and 40.8 mm, respectively. Treatment with deslorelin STI reduced the time interval to Ovulation significantly from 69.5±25.48 h to 42.7±12.35 h (p<0.001). The percentage of mares having ovulated within 48 h rose from 26.3% to 95.0%, respectively, for placebo and deslorelin STI (p<0.001). As a consequence, the duration of estrus in days and the percent of animals requiring more than 1 breeding were significantly reduced in deslorelin treated animals from 5.4 days to 4.6 days, and from 55.6% to 5.0%, respectively (p=0.009 and =0.001). The percent of mares pregnant from breedings at the treatment estrus (65.0% versus 44.4%) or the next estrus (83.3% versus 92.3%) was satisfactory and similar for deslorelin and placebo treated mares (p>0.005), and in 70.0% and 66.7% of these once or twice bred mares did pregnancies go to term and live foals were born. kw|Keywords|k]GnRH

Sammanfattning

En potent GnRH analog, deslorelinacetat, i form av ett implantat med korttidsfrisättning har provats i olika koncentrationer för att utvärdera möjligheten att ersätta HCG. Dosen 2.2 mg deslorelin per implantat befanns optimal. I ett kliniskt försök under 1992 behandlades 20 ston med deslorelin och 19 ston med placeboimplantat. Stona kontrollerades dagligen på förekommande brunsttecken och undersöktes rektalt och med ultraljud var 24 timme. Ston med folliklar ≥30 mm togs in i försöket. Implantatet sattes in subcutant på halsens vänstra sida med en 3 mm kanyl. Stona seminerades med färsk, kyld eller fryst sperma. Dräktighetsdiagnos ställdes via ultraljud på dag 18 och 38. Tidsintervallet mellan behandling och ovulation skilde signifikant mellan grupperna med 42,7 tim och respektive 69,2 tim för deslorelinbehandlade ston resp placebobehandlade. 95% behandlade ston ovulerade inom 48 tim mot 26,32% av de obehandlade. Brunstens längd förkortades signifikant (4,55 dagar mot 5,37) och därmed antalet semineringar / bctäckningstillfällen. Ingen skillnad i dräktighetsprocent samt fölningsprocent förelag. Inga eller mycket lindriga bieffekter i form av svullnad på halsen efter implantatet noterades.