Spezielle Untersuchungen zur Erhöhung der Zuverlässigkeit bei der Vorhersage des Ovulationszeitpunktes der Stute

Predicting the time of ovulation in the mare is an essential factor for the success of complex equine breeding programs involving frozen semen and embryo-transfer, by saving costs and labor time in equine stud farm medicine. The artificial use of hormones in studfarm practice has become a widely used tool to shorten the physiological long estrus of the mare and therefore enhance the success of equine breeding programs. Human chorionic gonadotropin (hCG) and GnRH implants are the most commonly used ovulation inducing agents. Despite their proven effectiveness, several disadvantages have been reported. Since there is no published data on the effect of the GnRH analogue Gonadorelin [6-D-Phe] (Gonavet Veyx ®) on ovulation in horses, it was the aim of this study to evaluate whether a single intramuscular injection is able to induce ovulation within 48 hours. A total of 82 mares received a treatment with 100 µg of Gonadorelin [6-D-Phe] as soon as estrus and a follicle-diameter >35 mm were detected. Manual rectal palpation and ultrasound examination were performed in 12-hour-intervals after the treatment. Eighty-five percent of mares ovulated within 48 hours. Of the 18 untreated control mares, 38% ovulated within 48 hours. The mean duration until ovulation in the Gonadorelin [6-D-Phe] and control group was 41±10,17 and 57±15,15 (p < 0,05) hours, respectively. The efficacy of Gonadorelin [6-D-Phe] in inducing ovulation within 48 hours post application increased from early breeding season in February - March (75,9 %) to mid and late season in April - July (89,95%). An influence of a mare`s age and/or reproductive status on the response to Gonadorelin [6-D-Phe] - treatment could not be observed. Gonadorelin [6-D-Phe] can be considered as a reliable and easy-to-use alternative to induce ovulation in the mare. Ovulation inducing agents are a useful tool in equine veterinary practice. Yet they are not able to replace the understanding of the physiologic changes of the preovulatory follicle to predict ovulation. Therefore, knowledge of these characteristic echotexture- and vascular changes becomes increasingly important. A total of 93 warmblood mares were used in this study to characterize the chronologic appearance of six discrete ultrasound parameters. Results reveal the solitary appearance of an anechoic band, loss of spherical shape and granulosa echogenicity to be poor indicators of an impending ovulation. However, in combination with serration of granulosa, apex formation or concentration of blood flow at the follicular base, a more precise prediction of ovulation is possible. Nearly all of the 71 ovulation-induced mares showed a combination of these parameters during the last hours before ovulation, a strong increase in percentage of mares with serration of granulosa and apex formation could be observed in the group of the control mares (n=17) at the last examination before ovulation (h -12). In the induced mares, 6 (± 4) hours before ovulation, a distinct formation of the serrated granulosa was visible; concentrated blood flow was noticeable at the follicular base 5 (± 3) hours before ovulation and as the last sign of impending ovulation, formation of an apex was detected at hour - 3,5 (± 2). Applying these results to spontaneously ovulating mares suggests serration of granulosa and the formation of follicular apex as the strongest indicators for an ovulation within the aformentioned hours.