Doctoral Dissertations

Date of Award

8-1975

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

R. L. Murphree

Committee Members

P. B. Coulson, D. O. Richardson, H. V. Shirley

Abstract

The objectives of this experiment are as follows: (1) to compare estrogen and progestin levels in the peripheral circulation to steroid levels in the follicular fluid, (2) to compare estrogen and progestin levels within small, medium, and large follicles, and (3) to obtain estrous dates along with morphological ovarian descriptions to use as a basis for the aforementioned comparisons. There were 180 Hereford heifers (6 per pen) used in this experi-ment. The animals were slaughtered when the mean thickness of backfat for the animals in a pen (6 per pen) reached 12 mm as measured by the somascope. Blood and follicular fluid were sampled and assayed simul-taneously for estrogen and progestin content using radioimmunoassay. Ovarian weights, corpus luteum weights, and follicle numbers were also recorded. Prior to slaughter, all heifers had been observed for estrous acitivities; and following slaughter, each pair of ovaries were classi-fied as to stage of growth (MGU) and inspected for abnormalities. Progestins and estrogens varied inversely throughout the MGU growth phases, and their patterns, levels, and ranges compared favorably with those previously described in the literature. Only progestin from medium follicles had secretion patterns similar to patterns in the plasma. There were significant differences (P<.001) in estrogen and progestin levels and patterns from different size follicles. Progestins varied significantly among MGU; however, estrogen was quite variable and showed no statistically significant relationship to MGU. Within size categories, steroid concentrations in the follicular fluid varied independently of volume changes. Follicle numbers per pair of ovaries remained constant for large follicles (one follicle per pair of ovaries) but varied within the small (12-100) and medium (1-6) classification. Morphological ovarian descriptions (MGU) were used as a basis for comparisons of estrogen and progestin levels in the peripheral circulation with steroid levels in follicular fluid and for comparisons between follicle sizes. Behavioral estrous cycles were extremely variable with 27 percent having short cycles (<15 days) and 37 percent having long cycles (>26 days). Approximately 50 percent of the animals were observed in standing estrus while the other half were not observed standing, but did display a color change in the KaMar Heatmount Detector. Within the MGU classifications, there was a disproportionality in numbers of heifers in MGU V and VI. This suggests that prior to and at the beginning of regression are the most variable stages in the corpus luteum morphology, thus emphasizing an explanation for variability in the cycle lengths that was observed in the heifer experiment.

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