Abstract
The effects of injected ovarian hormones on the corpus luteum of the estrual cycle were studied in heifers. One mg. of progesterone per lb. body weight in a single injection on day-1 of the cycle caused significant differences in corpus luteum weight, proportion of functional luteal cells, and progestogen concentration between treated and control corpora lutea on day-14. Positive associations between functional cells and weight, concentration and weight, and concentration and functional cells (r=0.46, 0.65, and 0.79, respectively) were significantly different from corresponding control correlations (r=−.22, −.10, and −.07, respectively). The same hormonal treatment on day-5 of the estrual cycle caused significant differences in proportion of functional cells and progestogen concentration, but not in corpus luteum weight. No significant change in associations of these characteristics was caused by this treatment. When heifers were given 250 meg. of estradiol-17 β per day from day-1 through day-13 of the estrual cycle, significant differences were found between treated and control corpora lutea for weight and proportion of functional luteal cells, but not for progestogen concentration. Associations between functional cells and weight, and concentration and weight were significantly altered from control values (r of 0.52 and 0.85 vs. −.22 and −.10, respectively), but the correlation between concentration and functional cells was not significantly affected by treatment (0.55 vs. −.07). Copyright © . .