Physiological mechanisms of ovarian follicular growth in pigs — A review

Abstract

Follicular growth after antrum formation is determined by folliclestimulating hormone (FSH). Only two ways are possible for recruited follicles, continuing development or atresia. In gilts, intensive ovarian follicular growth begins between 60 and 100 days of age, and fluctuations of the ovarian morphological status last about 20 days; however, at that time there are no really large follicles. Final follicular development is under luteinising hormone (LH) control; this is why the attainment of puberty is related to an increase in serum oestradiol to a level that causes a preovulatory surge of this gonadotropin. The pool of follicles at the beginning of the oestrous cycle is about 30-40, most of which are small (< 3 mm) and growing. Then, the pool of follicles increases to about 80 in the mid-luteal phase but about 50 of them are small and 30 are medium sized (3-6.9 mm). Some of these follicles are in the growing phase, but some are atretic. Between days 7 and 15 of the oestrous cycle the percentage of atretic follicles fluctuates between 12 and 73%. At that time there are no large (> 7 mm) follicles because of the suppressing effect of progesterone. The number of small follicles declines after luteolysis. From the pool of medium follicles, large follicles are selected under the influence of LH, but about 70% of the medium-sized follicles become atretic. Because of the long-lasting selection process there is a significant heterogeneity in the diameter of large follicles in oestrus. However, the number of follicles correlates with the number of corpora lutea after ovulation. Individual follicular development and the relationship between follicles are still poorly known. The use of ultrasonography may give a closer insight into these phenomena.

Identification of measures predictive of age of puberty onset in gilts

“…In addition to BW, other quantifiable markers that are more directly and biologically related to factors contributing to puberty onset may be predictive of age at puberty as well if measured at the appropriate stage of a gilt’s life. We previously observed significant follicular variation in gilts sacrificed at approximately 90 to 100 d of age ( Pearce et al, 2013 ), substantiating others observations that variation among gilts with respect to the beginning of follicular growth begins at approximately 60 to 100 d of age ( Schwarz et al, 2008 ). Our observation included that those gilts with greater tertiary follicle development also appeared to demonstrate greater reproductive tract wet weight, presumably the result of elevated estrogen in circulation.…”

The effect of bpV(HOpic) on in vitro activation of primordial follicles in cultured swine ovarian cortical strips

“…Folliculogenesis is one of the most important physiological events that significantly influences the success of animal breeding. Researchers and breeders are therefore interested in its regulatory mechanisms as well as in the possibility of manipulating that process (Schwarz, Kopyra, & Nowicki, ).…”

Biological and technological background of estrus synchronization and fixed-time ovulation induction in the pig

“…Follicular development in gilts and sows has been reviewed in detail elsewhere (Prunier and Quesnel, 2000;Schwartz et al, 2008). In gilts the follicle cohort destined to ovulate is stimulated by increased postovulatory FSH, but under the influence of the high luteal progesterone (P4) concentration during dioestrus follicles do not grow to ovulatory size.…”