Year: 2007
Type: dissertation
Abstract: The wave-like developmental pattern of follicles ≥1 mm in temporal relationship with follicle stimulating hormone (FSH) and the existence of 2-and 3-waves of follicular development during an interovulatory interval (IOI) have been clearly defined in cattle.However, information about the developmental pattern of antral follicles <1 mm and the repeatability of the wave pattern (2-or 3-wave IOI) is lacking.Using approaches such as immunization against GnRH (to suppress circulating concentrations of FSH) and histomorphometric study of ovarian tissues collected from cyclic heifers on different days after ovulation, the developmental pattern of antral follicles <1 mm and the role of FSH in their development were studied in heifers.Ultrasonographically acquired follicular data were used to determine the repeatability of 2-and 3-wave patterns and the effect of season on the wave patterns.The ovulatory follicle in 3-wave IOI is exposed to a shorter term high-progesterone environment than that of 2-wave IOI, and it has been argued that the less-aged ovulatory follicle of 3-wave IOI yields a more fertile oocyte than the 2-wave IOI.The developmental competence of oocytes in preovulatory follicles of 2-versus 3-wave IOI was compared using in vivo environments created to mimic short-term low-and high-progesterone environments similar to 2and 3-wave IOI, respectively.The developmental competence of oocytes in persistent dominanttype follicles was also determined.The vaccination against GnRH attenuated FSH surges but did not suppress the basal circulating concentrations of FSH.The attenuation of FSH surges suppressed the wave-like emergence of follicles ≥4 mm but not of the antral follicles <4 mm.The study revealed an inverse relationship between the mean and peak circulating concentrations of FSH and the number of follicles recruited into ≥1 mm size category.Histomorphometric study revealed that antral follicles <1 mm developed in a wave-like fashion in response to a rise in the circulating concentrations of FSH.After treatment with exogenous FSH, the growth rate of follicles in GnRH-immunized heifers was similar to controls.The duration of IOI was predictive of the wave pattern (i.e., 2-or 3-wave IOI), and the pattern was repeatable within individuals throughout the year.The dominant follicle of Wave 1 in 2-wave IOI had a longer duration of dominance than in 3-wave IOI.Hence, the dominant follicle of Wave 1 may have a primary role in the regulation of 2-and 3-wave patterns.Greater iii attrition of follicles in 3-wave IOI, due to the emergence of an extra wave compared to 2-wave IOI, may contribute to earlier follicular depletion and onset of reproductive senescence in heifers with primarily a 3-wave pattern.The fertilization capacity of oocytes that were exposed to the short-term low-progesterone environment (i.e., similar to the early growing phase of the ovulatory follicle of 3-wave IOI) was increased, but the developmental competence postfertilization was not different from oocytes that were exposed to a short-term high-progesterone environment (i.e., similar to the early growing phase of preovulatory follicle of 2-wave IOI).Multiple follicles developed under the prolonged-low progesterone environment, but failed to ovulate.Gregg Adams, who has not only provided me the best guidance but also supported me at the personal level.Under his supervision, I have earned my master and doctorate degrees with a bonus of self-confidence.I would take this opportunity to thank you Dr. Jaswant Singh for all your help and hospitality during my initial days in Saskatoon, for the best time we spent together in the basement of Osler street house.I am indebted to you
Author: R.S. Jaiswal
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1565678662