Cyclic Changes in Bovine Vesicular Follicles

Abstract

Nineteen pairs of bovine ovaries obtained at representative stages during the estrous cycle and pregnancy were evaluated histologically in an effort to identify quantitative cyclic changes in the vesicular follicles. All follicles with visible antra were counted, measured and classified according to their morphological features. The follicular counts for different reproductive periods and days within periods were compared. The mean relative proportions of normal and atretic follicles during the estrous cycle and pregnancy were 23.7 and 76.3%, and 32.6 and 67.4%, respectively. The mean total counts for normal and atretic follicles per pair of ovaries during the estrous cycle and pregnancy were 93.9 and 287.6, and 96.2 and 196.3, respectively. Normal follicles larger than 5 mm. were not present in ovaries obtained during the luteal phase of the cycle; however, atretic follicles larger than 5 mm. were present in the ovaries during the entire cycle. The growth of the follicle from one size class to another appears to be continuous and independent of the stage of the cycle. The number of normal follicles during early pregnancy was similar to that found in ovaries representing the luteal phase of the cycle. A progressive decrease in the number of normal follicles was evident during the late stages of pregnancy. Normal follicles larger than 2 mm. were absent by 243 days of pregnancy. The presence of a significantly (P<.05) higher mean proportion of atretic follicles and a higher proportion of late atresia during the cycle indicates a higher rate of follicular turn-over during this period than during pregnancy. Copyright © 1968. American Society of Animal Science . Copyright 1968 by American Society of Animal Science