CONICET | Buscador de Institutos y Recursos Humanos

Recombinant equine FSH (reFSH) has been shown to be effective at inducing superovulation and production of multiple embryos in cycling and anestrus mares. Moreover, supplementation with reLH during the reFSH treatment has resulted in improved embryos recovery rates. The objective of this study was to evaluate the effect of reLH supplementation during reFSH treatment and of different ovulation inducing agents (Deslorelin and reLH) on the superovulatory response, embryo recovery, and pregnancy rates after embryo transfer during the regular breeding season. Polo Argentino cycling mares were randomly assigned to one of four treatment groups. Group 1: reFSH/reLH + Deslorelin (n=12), Group 2: reFSH/reLH + reLH (n=12), Group 3: reFSH + Deslorelin (n=12), and Group 4: reFSH + reLH (n=12). Four days after ovulation, daily ultrasonography was performed to monitor ovarian follicular growth. Once the largest follicle was between 20 and 25 mm in diameter, treatment was initiated (day 0). reFSH (0.65 mg i.m., AspenBio Pharma Inc.) was administered twice daily for 3 days and once daily thereafter until a follicle of 32 (Groups 1-2) or 35 mm (Groups 3-4) was detected. On day 2 of treatment, all mares received Sodium Cloprostenol (500 μg i.m. Schering-Plough). Mares in groups 1 and 2 received reLH (1.5 mg i.v., AspenBio Pharma Inc.) twice daily at the time a 29 mm follicle was detected and three times during one day once follicles reached 32 mm in diameter. Mares were allowed to coast for 24 to 36 hours after a follicle >35 mm was detected. Then, either 1.5 mg Deslorelin (i.v.; Groups 1 and 3) or 3 mg reLH (i.v.; Groups 2 and 4) was administered to induce ovulation. Mares not ovulating in a 48 hour period also received 2,500 IU hCG (i.v.). Breeding by artificial insemination was performed at the time of Deslorelin or reLH administration and every 48 hours until ovulation(s) were detected. Eight days after the first ovulation, standard transcervical embryo recovery was performed and the embryos transferred based on availability of naturally synchronized recipients. Analysis was performed by ANOVA considering a 2x2 factorial design with stimulatory treatment (ST: reFSH/reLH vs reFSH), ovulation inducing agent (OIA: Deslorelin vs reLH), and their interaction as the main effects. Results for each individual group are presented in table 1. A positive stimulatory response (development of more than one follicles>35 mm) was observed in 42 of the 48 mares treated. No significant differences were detected for any of the variables analyzed. Overall, an average of 6.5 preovulatory follicles (>35 mm) and 4.7 ovulations per treated mare was recorded. Ovulations were detected in 44 (92%) of the 48 mares, with 35 (73%) and 31 (64%) mares ovulating more than one and two follicles, respectively. The four mares that did not ovulate developed hemorrhagic anovulatory follicles (HAFs). HAFs were also observed in three mares that did not ovulate all the preovulatory follicles present. Embryos were recovered in 27 (59%) of the 46 flushings performed to date, with an average of 1.6 embryos per mare but a great variability in results (Range: 0-10 and Coefficient of Variation: 136%). The embryo recovery rate averaged 0.35 embryos per ovulation. Transfer of 59 embryos resulted in 42 pregnancies (70%). A comparison of this study results to natural cycle embryo flushing records from the same mares in previous seasons (514 flushings in 5 seasons) indicates that the average number of embryos recovered per flushing more than doubled with the superovulatory treatments (1.63 vs 0.69) while the pregnancy rates remained similar (0.70 vs 0.60). In summary, treatment of cycling mares with recombinant equine gonadotropins induces a robust follicular development and ovulation response and allows for production of multiple embryos per flusHing; however, the high variability in individual response indicates that further optimization of the treatment protocols is still necessary.

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