Variations in Some Biochemical and Histological Characteristics of Bovine Corpora Lutea during Early Pregnancy

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Abstract
Two experiments involving 40 heifers were used to study the level of function of the corpus luteum during early pregnancy. Experiment one was a comparison of day-14 of the estrual cycle and day-14, -28, and -42 of pregnancy. Experiment two compared day-18, -23, and -28 of pregnancy. Progesterone and total progestogen were lower (P<0.01) on day-28 and -42 of pregnancy than on day-14. A significant (P<0.01) negative regression of progesterone and total progestogen content on day of pregnancy up to day-28 was found ( — 6.07 and —6.32 mcg., respectively). These regressions appeared to be linear. The level of 4-pregnene-20β-o1-3- one did not appear to vary with stage of pregnancy. Free cholesterol concentration increased significantly between day-14 and -28, but tended to return toward the day-14 level by day-42. The regression of free cholesterol between day-14 and -28 of pregnancy was 35.6 mcg. per gram per day (P<0.01) and appeared to be linear. Mean concentrations of DNA were not different, but RNA decreased with increasing length of gestation. A decreased percentage of functional cells was apparent histologically at day-23 of pregnancy and at later stages as compared to day-14 or -18 of pregnancy. The latter named stages in turn had fewer functional cells than the unbred heifers on day-14 of the estrual cycle. Copyright © . .