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Title: Dynamics of follicle growth in the sheep
Author: De Souza, Carlos José Hoff
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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Using ewes with an ovarian autotransplant, the diameter of individual follicles and corpora lutea was measured by ultrasound scanning, to characterise the pattern of development of antral follicles over 2.5 mm, in relation to gonadotrophin and ovarian hormone concentrations in jugular and ovarian venous blood. Studies were conducted to investigate the effects of season, age and the action of a major gene involved in increased prolificacy in sheep (FecB) on the dynamics of follicular growth and its hormonal regulation. The results showed that the final stages of maturation of dominant follicles in sheep during the oestrous cycle and anoestrus occurs in a succession of waves of follicular growth. During the luteal phase 3 waves emerge on day 2, 7 and 11 post-LH surge. During the follicular phase, most of the follicles that ovulate after the LH surge originate from follicles above 5 mm in diameter at the time of luteal regression, but additional smaller follicles can be recruited during the follicular phase. During the follicular and early luteal phase, when LH pulse frequency is elevated, follicles achieved dominance by secreting large amounts of oestradiol and inhibin A, depressing FSH concentrations below threshold levels. During the second and third wave of follicular development of the luteal phase a similar pattern of FSH secretion was evident but the relationship between the secretion of oestradiol and inhibin A was less clear. Despite these endocrine differences, the mechanism of follicular selection operated in each of these waves as the number of dominant follicles was similar to the ovulation rate. Similar investigations in ewes carrying the Booroola FecB gene, showed that gene carrier ewes produce more follicles that mature earlier at smaller size, without any differences in the concentration of FSH and the ovarian secretion of oestradiol, androstenedione and inhibin A compared to non-carrier animals. This suggests that the Booroola gene acts at an ovarian level modulating the gonadotrophin signal to increase the number of follicles selected. In order to study the effect of age in pituitary-ovarian function, the dynamics of follicular diameter were studied in old ewes (12-13 years) with ovarian autotransplants and the results of gonadotrophin and ovarian hormone concentrations compared to those obtained from the same animals 6 years previously.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available