RELATIONSHIPS BETWEEN FSH AND OVARIAN FOLLICULAR WAVES DURING THE LAST 6 MONTHS OF PREGNANCY IN CATTLE

Follicles were monitored daily by ultrasound and blood samples for FSH assay were collected daily from eight heifers from day 90 of pregnanc y to the emergence of the first postpartum follicular wave. Follicles greater than or equal to 6mm in diameter emerged in groups or waves in each heifer (P < 0.005). Follicular waves developed rhythmically thro ughout pregnancy, except that follicles greater than or equal to 6 mm were not detected during the last 21.6 +/- 2.4 (mean +/- SEM) days of pregnancy. The characteristics of the first follicular wave after day 90 were similar to previous reports for days 10-100. However, between months 4 (days 90-119) and 5, there was a decrease (P < 0.05) in month ly means for maximum diameter (mm) of largest (11.1 +/- 0.5 versus 9.5 +/- 0.5) and second largest (8.0 +/- 0.3 versus 6.9 +/- 0.2) follicle s, duration of the interwave interval (8.1 +/- 0.4 versus 6.6 +/- 0.3 days), and number of follicles per wave (3.7 +/- 0.4 versus 2.5 +/- 0. 4). Averaged over all follicular waves during months 4-9, the concentr ations of FSH normalized to the emergence of a follicular wave increas ed (P < 0.05) over the 3 days before emergence, reached peak values on the day of emergence of the future dominant follicle at 4 mm, and dec reased (P < 0.05) over the 3 days following emergence. Surges in FSH c oncentrations occurred throughout pregnancy, but during the last 30 da ys of pregnancy the number of surges was reduced and each heifer had o ne or two ineffective surges (no follicular wave detected). The tempor al relationship between FSH surges and emergence of waves was closer ( P < 0.01) than would be expected if the two events were independent. S urges of FSH occurred rhythmically even when there was no follicular r esponse (no follicle > 5 mm). In association with waves in which the l argest follicle reached greater than or equal to 10 mm compared with 6 -9 mm, there was greater depression in the FSH nadir, longer intervals from FSH peak to nadir, and longer intervals between adjacent FSH pea ks and adjacent waves.