Selection, dominance and atresia of follicles during the oestrous cycle of heifers

Abstract

This study examined the correlation between measurement of follicle growth by ultrasound,

Parturition to resumption of ovarian cyclicity: comparative aspects of beef and dairy cows

“…Each wave of growth involves emergence, selection and dominance followed by either atresia or ovulation. Emergence of a follicle wave is defined as growth of a cohort of follicles ⩾ 5 mm in diameter and coincides with a transient increase in FSH secretion (Adams et al, 1992;Sunderland et al, 1994). Follicle selection occurs in the face of declining FSH concentrations and is the process by which the growing cohort of follicles is reduced to the ovulatory quota for the species (in cattle it is generally one; Sunderland et al, 1994).…”

“…Emergence of a follicle wave is defined as growth of a cohort of follicles ⩾ 5 mm in diameter and coincides with a transient increase in FSH secretion (Adams et al, 1992;Sunderland et al, 1994). Follicle selection occurs in the face of declining FSH concentrations and is the process by which the growing cohort of follicles is reduced to the ovulatory quota for the species (in cattle it is generally one; Sunderland et al, 1994). The selected follicle survives in an environment of reduced FSH owing to the development of LH receptors in the granulosa cells (Xu et al, 1995;Bao et al 1997) and increased intrafollicular bioavailable IGF-I (Austin et al, 2001;Canty et al, 2006).…”

“…The increased bioavailable IGF-I is achieved by reduced IGF-I-binding proteins (IGFBP) because of increased IGFBP protease activity. Dominance is the phase during which the single selected follicle actively suppresses FSH concentrations and ensures the suppression of all other follicle growth on the ovaries (Sunderland et al, 1994). The fate of the dominant follicle is then dependent on the prevailing LH pulse frequency during the dominance phase.…”

“…The fate of the dominant follicle is then dependent on the prevailing LH pulse frequency during the dominance phase. In the presence of elevated progesterone (luteal phase of cyclic animals), LH pulse frequency is maintained at 1 pulse every 4 h and the dominant follicle undergoes atresia; in the follicular phase (preovulatory period in cyclic animals), the LH pulse frequency increases to 1 pulse per hour and this stimulates final maturation, increased oestradiol concentrations and positive feedback on gonadotrophin-releasing hormone (GnRH), LH (and FSH), in a surge that induces ovulation (Sunderland et al, 1994). Normal follicle waves have an inherent lifespan of 7 to 10 days' duration from the time of emergence of a wave until emergence of the next wave (indicating either ovulation or physiological atresia of the dominant follicle).…”

Follicular dynamic and ovulation in cattle – a review

“…ADAMS (1999) concluded from the available data that greater than 95 % of oestrous cycles are composed of either two or three follicular waves. Normally three to six follicles with a diameter of 4 to 5 mm occur after recruitment of follicles into in a follicular wave (SAVIO et al, 1988;SIROIS and FORTUNE, 1988;SUNDERLAND et al, 1994). However, the number of follicles, which are recruited in a wave seems to be higher (ADAMS, 1999;BELLMANN, 2001).…”