CONTINUED PERIODIC EMERGENCE OF FOLLICULAR WAVES IN NON-BRED PROGESTERONE-TREATED HEIFERS

The hypothesis was tested that continued periodic emergence of anovulatory follicular waves in pregnant heifers is associated with continued progesterone production. Daily transrectal ultrasonic examinations were used to monitor the diameter profiles of dominant follicles in 19 bred heifers and six non-bred progesterone-treated heifers; 15 of the 19 bred heifers became pregnant and were assigned to a pregnent-control group. Beginning on Day 10 (ovulation = Day 0), non-bred heifers were given a daily injection of 150 mg of progesterone in corn oil vehicle and bred heifers were given corn oil vehicle only. Treatment continued until approximately Day 100, except for non-pregnant heifers, in which treatment was discontinued at reovulation. In the non-bred progesterone-treated group, development of the dominant follicle for Waves 1-10 in relation to side of ovulation and development of successive dominant follicles in relation to side of the previous dominant follicle occurred with equal frequency (not significantly different) in the same and opposite ovaries. In both the pregnant-control and non-bred progesterone-treated groups, the maximum diameter of the dominant follicle of Wave 2 (means +/- SEM, 12.7 +/- 0.4 mm and 10.1 +/- 0.4 mm, respectively) was smaller (P < 0.05) than for Wave 1 (15.1 +/- 0.3 mm and 14.8 +/- 0.5 mm). The maximum diameter of the dominant follicle of Wave 2 in the non-bred progesterone-treated group (10.1 +/- 0.4 mm) was smaller (P < 0.05) than in the pregnant-control group (12.7 +/- 0.4 mm). Similarly, the day-to-day profile of the dominant follicle of Wave 2 was less pronounced in the progesterone-treated group (P < 0.003). The dominant follicle of Waves 3-10 (pregnant-control group) and Waves 4, 5, 7 and 9 (non-bred progesterone-treated group) also was smaller (P < 0.05) than for Waves 1. The interval between successive waves was not different between pregnant-control (mean 8.9 +/- 0.2 days) and non-bred progesterone-treated (9.6 +/- 0.3 days) groups. The hypothesis that the continued periodic emergence of anovulatory follicular waves in pregnant heifers was associated with continued production of progesterone was supported by the continued periodic emergence of waves in the non-bred progesterone-treated heifers.