Numbers of Antral Follicles During Follicular Waves in Cattle: Evidence for High Variation Among Animals, Very High Repeatability in Individuals, and an Inverse Association with Serum Follicle-Stimulating Hormone Concentrations1

Abstract

The extent, causes, and physiological significance of the variation in number of follicles growing during ovarian follicular waves in human beings and cattle are unknown. Therefore, the present study examined the variability and repeatability in numbers of follicles 3 mm or greater in diameter during the follicular waves in bovine estrous cycles, and we determined if the variation in number of follicles during waves was associated with alterations in secretion of FSH, estradiol, inhibin, and insulin-like growth factor I (IGF-I). Dairy cattle were subjected to twice-daily ultrasound analysis to count total number of antral follicles 3 mm or greater in diameter throughout 138 different follicular waves. In another study, blood samples were taken at frequent intervals from cows that consistently had low or very high numbers of follicles during waves and were subjected to immunoassays. Results indicate the following: First, despite an approximately sevenfold variation in number of follicles during waves among animals and marked differences in age, stage of lactation, and season of the year, a very highly repeatable (0.95) number of follicles 3 mm or greater in diameter is maintained during the ovulatory and nonovulatory follicular waves of individuals. Second, variation in number of follicles 3 mm or greater in diameter during waves and the inverse association of number of follicles during waves with FSH are not directly explained by alterations in the patterns of secretion of estradiol, inhibin, or IGF-I. Third, ovarian ultrasound analysis can be used reliably by investigators to identify cattle that consistently have low or high numbers of follicles during waves, thus providing a novel experimental model to determine the causes and physiological significance of the high variation in antral follicle number during follicular waves among single-ovulating species, such as cattle or humans.

Studies of granulosa cell maturation in dominant and subordinate bovine follicles: novel extracellular matrix focimatrix is co-ordinately regulated with cholesterol side-chain cleavage CYP11A1

“…Large variation exists between animals in terms of number of follicles per wave (range 11-54), principally due to differences in the numbers of small follicles (those w3 mm in diameter). The number of follicles per wave is relatively consistent within individual cows and does not correlate with either two or three wave patterns per oestrous cycle, or with dominant follicle development (Burns et al 2005). In each follicular wave, the future dominant follicle enters the wave w6 h earlier than other follicles in the cohort, which translates into a size advantage at the end of the common growth phase (Jaiswal et al 2004).…”

Oocyte-Somatic Cell Interactions and Ovulation Rate: Effects on Oocyte Quality and Embryo Yield

“…30 In sheep, the numbers of primordial follicles formed during fetal life (ie by 120 days of gestation) is highly variable between individual ewes (~23000-350000). 31 In cattle, between 14 and 33 months of age, there is a 7-fold variation in number of antral follicles 4 mm diameter between animals, but within individual animals, this number is highly repeatable (0.95 where 1 = fully repeatable).…”

Ovarian follicle growth dynamics during the postpartum period in Holstein cows and effects of contemporary cyst occurrence

“…This was mainly because of high variability among cows and also among consecutive follicular waves in individual animals. Burns et al (2005) also stated high variability among individual animals. According to them, variance in the number of follicles developed during the estrous cycle could have an important but little understood role in fertility regulation in single-ovulating species, such as cattle.…”