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      Effect of progesterone on GnRH-mediated LH release, oocyte quality, and fertility in cattle

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      Date
      2008
      Author
      Dias, Fernanda Caminha Faustino
      Type
      Thesis
      Degree Level
      Masters
      Metadata
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      Abstract
      The objective was to investigate the effects of progesterone (P4) on luteinizing hormone (LH) release, follicle development, and oocyte competence in cattle. We tested the general hypotheses that: 1) The suppressive effect of P4 on gonadotrophin releasing hormone (GnRH)-mediated LH release can be overcome by increasing GnRH dose or pre-treatment with estradiol (E2); and 2) a shorter period of P4 exposure during the growing phase of the ovulatory follicle improves oocyte competence and fertility after fixed-time artificial insemination or superstimulation in cattle. In the first experiment, heifers (n=22) were treated with 100 or 200 µg of GnRH or pretreated with E2 prior to administration of GnRH during high or low circulating P4 concentrations to characterize LH release (Chapter 2). Increasing the dose of GnRH did not alter LH secretion; however, E2 pretreatment overcame the suppressive effect of high P4 on LH secretion. Cattle with lower (n=11) P4 concentrations had higher circulating LH concentrations than those with higher P4 concentrations (n=11), and tended to have higher ovulation rates. Two experiments were conducted to determine the effect of the duration of P4 exposure during the ovulatory wave on fertility followed fixed-time artificial insemination or superstimulation. In the first experiment (Chapter 3), the dominant follicle was allowed to grow for 3 days (n=181) or 6 days (n=184). Six days of growth resulted in a larger dominant follicle, but in both groups, ovulatory follicles had similar capacities to ovulate and establish pregnancy. In the second experiment (Chapter 4), multiple follicles were allowed to grow for 3 or 6 days by 8 or 14 injections of FSH (at 12-hour intervals). There was no difference between groups for ovulation rate or total ova/embryo recovery rate. Although the 3-day group had higher embryo quality at slaughter (4 days after insemination), further development (7, 9, and 10 days after insemination) did not differ among groups. The effect of FSH starvation following 4 days of FSH treatment (Chapter 4) resulted in loss of ovulatory capability. Overall, a shorter duration of P4 exposure during ovulatory follicle growth did not improve fertility after fixed-time AI or oocyte competence after superstimulation.
      Degree
      Master of Science (M.Sc.)
      Department
      Veterinary Biomedical Sciences
      Program
      Veterinary Biomedical Sciences
      Supervisor
      Singh, Jaswant
      Committee
      Singh, Baljit; Palmer, Colin; Mapletoft, Reuben J.; Kastelic, John; Adams, Gregg P.
      Copyright Date
      2008
      URI
      http://hdl.handle.net/10388/etd-06262008-170154
      Subject
      cattle
      fertility
      follicle
      GnRH
      LH
      pregnancy rate
      progesterone
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      • Graduate Theses and Dissertations
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