Effects of Dosage and Treatment Phase of Two GnRH Analogues at the Estrous Stage on Superovulation in Ewes

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This study investigated two different GnRH analogues (fertirelin acetate or buserelin acetate) with two different dosages (Experiment 1: spring) and different injection times at estrus in superovulated ewes (Experiment 2: autumn). Effects on ovarian response and recovered embryo quality were compared among the treated ewes in each season. All ewes were pre-treated with vaginal sponges impregnated with synthetic progesterone for 12 days and were injected intramuscularly with 20 mg pFSH and 250 IU eCG at 2- and 1-day before the sponge removal, respectively. The ewes were observed for estrous behavior from the time of sponge removal every 6 h, and were treated at estrous detection by intramuscular injections as follows: in Experiment 1 (n=34), 1 ml of Conceral (containing 50 μg fertirelin acetate per 1 ml) (Treatment Group 1), 2 ml of Conceral (Treatment Group 2), 1 ml of Estomal (containing 4.2 μg buserelin acetate per 1 ml) (Treatment Group 3), 2 ml of Estomal (Treatment Group 4), and 1 ml of 0.6% NaCl solution (Treatment Group 5; control), and in Experiment 2 (n=27), Treatment Groups 1 and 3 as in Exp. 1. The ewes that had not shown estrous behavior within 24 h after the sponge removal were treated with either Conceral or Estomal at 24 h. The ewes were inseminated intrauterinally with fresh-diluted semen by means of a laparoscope 32 to 36 h after sponge removal and ovarian response was observed. Embryo recovery were performed under surgical operation on the 5th day after the insemination. In Experiment 1, the mean ovulation rate in Treatment Group 3 tended to be higher than in Treatment Groups 2 and 4. The incidence of abnormal corpora lutea (CL) in Treatment Group 2 tended to be higher than in the others. In Experiment 2, the ewes were divided into two groups by the interval between sponge removal and onset of the estrous sign. The mean ovulation rate in the ewes that did not show estrous signs within 24 h after sponge removal and were treated with 1 ml of Estomal was significantly lower than in the others (P<0.05). The present study indicates that the dose of 2 ml of the two GnRH analogues may be over-dosage and has a detrimental effect on ovarian response. It also suggested that the timing of GnRH injection affects the ovulation rate and embryo recovery results.
日本繁殖生物学会の論文

Effects of Dosage and Treatment Phase of Two GnRH Analogues at the Estrous Stage on Superovulation in Ewes

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