ACCELERATION AND TIMING OF FERTILE OVULATION IN CYCLIC MARES WITH A DESLORELIN IMPLANT

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 implan t as a negative control. A total of 39 mares received treatments at ad mittance with pre-randomized implants containing either 2.2 mg or 0 mg deslorelin. Mares were teased daily and examined rectally with ultras ound at 24 h intervals to determine time to ovulation and duration of estrus. The number of breedings and the pregnancy rate at 18 (+/-3) an d 35 (+/-3) days were recorded, as were systemic side effects and loca l reactions at the implantation sites. Pregnancies resulting from bree dings during the treatment estrus and/or from breedings during the nex t estrus were followed and the early and late pregnancy loss rate, the number of pregnancies going to term and of live-born foals was record ed. Mean follicle diameter at treatment was not significantly differen t 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+/-12.3 5 h (p<0.001). The percentage of mares having ovulated within 48 h ros e 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 perce nt of animals requiring more than 1 breeding were significantly reduce d 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 p regnant 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 liv e foals were born.