Date of Award
Doctor of Philosophy
Productivity efficiency in the livestock sector depends upon reproduction success at the farms. Evaluation of follicle and corpus luteum hemodynamics by color-Doppler ultrasonography is becoming more commonly used in cattle reproductive management. Improved understanding of the relationships between size and blood flow of the preovulatory follicle (POF) and corpus luteum (CL) with the subsequent systemic progesterone production, and the impact of those factors on fertility, would provide information to help maximize fertility in cattle reproduction. Three studies were conducted in this dissertation with the following general objectives: I) evaluate the relationships between follicle and corpus luteum dimensions and blood flow, and the influence of follicle size and wall blood flow on systemic progesterone production by the subsequent CL; II) study the relationships between follicle wall blood flow within different follicle size categories, between cows and heifers, and the effect on pregnancy rates; and III) develop a novel and reliable objective method for evaluation of follicle wall blood flow. In study one, high positive correlations were found among all POF and CL end points, and progesterone concentrations. Ratios of POF, CL, and progesterone end points ranged from moderate to strong positive correlations. Linear regression dispersions among selected POF and CL end points and progesterone concentrations showed high significance when using POF dimensions to estimate CL dimensions as well as POF blood flow to estimate CL size and blood flow, and plasma progesterone concentrations. In study two, cows had larger and more vascularized follicles than heifers. Pregnant cows had larger follicles and tended to have more vascularized follicles than non-pregnant cows. Follicle blood flow was greater in the large follicle category compared with the small follicles, and tended to be greater than medium-size follicles. Moderate to strong correlations were found between follicle blood flow and small, medium, and large follicles. Pregnancy rates were similar among follicle diameter categories. In study three, a novel objective method (wall under flow, WUF) for evaluation of follicle wall blood flow using color-Doppler ultrasonography was tested. Results indicated that due to differences in follicle morphology and in area and location of the blood flow, the objective pixel analysis previously reported in the literature for evaluation of CL blood flow cannot be translated as a gold standard test to objectively evaluate blood flow in follicles. The WUF was a superior method to evaluate follicle wall blood flow when compared with other methods. Furthermore, pixel area method did not sustain the validation of subjective evaluations of follicle wall blood flow. In conclusion, this work demonstrated novel linear relationships among POF and CL end points which can be used to estimate the subsequent progesterone production by the CL. Additionally, POF wall blood flow was closely associated with an increase in follicle diameter; smaller follicles had lower blood flow when compared with larger follicles. Moreover, the WUF was a more reliable method to objectively evaluate follicle wall blood flow in cows than the pixel area method.
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