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. <p>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. <p>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.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-06262008-170154 |
| Date | 08 July 2008 |
| Creators | Dias, Fernanda Caminha Faustino |
| Contributors | Singh, Baljit, Palmer, Colin, Mapletoft, Reuben J., Kastelic, John, Adams, Gregg P., Singh, Jaswant |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-06262008-170154/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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