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Induction of ovulation in deeply anestrous mares by different doses of a gonadotropin-releasing hormone analogue (CH 690030)
Abstract
A total of 54 mares in seasonal anestrous were assigned to 5 groups to receive implants containing one of the 5 doses (0, 0.9, 1.8, 3.6, and 5.4 mg/head in group order) of a GnRH analogue (CH 690030 or Goserelin) on January 28. Five mares classified as transitional mares when implants were given ovulated at a time between 11 and 21 days after the onset of treatment regardless of dose, followed by normal CL formation. Reciprocal changes between an increased LH concentration and a decreased FSH concentration commenced 6 days before ovulation, when follicles initiated rapid growth. Ovulated mares showed a gradual rise in LH concentrations with a 5-day duration of high LH concentrations, reaching a peak during the peri-ovulatory period and followed by a slow decline without returning to the pre-treatment value at the end of the 30day post-treatment period. The change in FSH was first a rapid rise then an obvious drop with a nadir 3-5 days before ovulation and then a low level maintained until the end of the study. Mares receiving a dose of 3.6 mg/head had a higher mean post treatment LH concentration, a higher mean LH peak value, a lower mean post-treatment FSH concentration, and a lower mean FSH peak value than the controls (P < 0.05). The intervals to the peaks of gonadotropins and maximum follicles were also significantly shorter for mares dosed with 3.6 mg/head than for the controls (P < 0.05). The mean LH peak value for mares that ovulated (76.4 ︢14.5 ng/ml) was significantly greater than the controls (19.3 ︢3.8 ng/ml) and mares dosed with 0.9 mg/head (28.2 ︢3.3 ng/ml) which did not ovulate (P < 0.05). A dose of 5.4 mg/head did not cause responses different from those induced by a dose of 3.6 mg/head. Doses ranging from 1.8 mg/head to 3.6 mg/head are recommended for further investigation based on changes in gonadotropin concentrations and follicle diameters after Goserelin treatment. Results of this trial do not show any encouragement for giving Goserelin implants to anestrous mares in late January. The low LH concentrations in 75% of all the mares that failed to ovulate and an early date of onset of treatment in the present study may account for the low ovulation rate. The adverse weather conditions associated with heavy rain and lower temperature may have contributed to the failure to ovulate.
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Citation
Chen, Fang-Jane Jennifer (1993). Induction of ovulation in deeply anestrous mares by different doses of a gonadotropin-releasing hormone analogue (CH 690030). Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1993 -THESIS -C518.
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