Reproduction in Domestic Animals

50 M Mihm and ACO Evansguaranteed to result in a DF. Thus, mares and womenshare very similar wave dynamics: (1) The occurrence ofmajor (leading to selection of a DF) anovulatory wavesduring the luteal phase in 20% (mares) or 30% (women)of cycles. (2) The occurrence of minor waves (whichdescribes the emergence and growth of cohort folliclesfollowed by their regression without DF selection)during both the luteal and follicular phases of the cycle,albeit the percentage differs between mares (almost100%) and women (only 57%). (3) The high percentageof pre-deviation follicles (mares 37%, women 48%)which are follicles that emerge with or ahead of the DFin ovulatory waves, reach DF size 1 day before theovulatory DF but begin to regress at the time ofdeviation of the ovulatory DF. At emergence anddeviation, respectively, cows and women share verysimilar cohort (3–6 mm), largest subordinate (7–8 mm)and DF diameters (8.5–10 mm) determined by ultrasound.Only women show an enhanced growth rate ofthe DF and regression rate of SF following deviation,while in mares and cows growth rates of DF aremaintained at rates seen before deviation (Ginther et al.2001b, 2004a). While ‘local’ effects of DF on antralfollicles from the ipsi- vs the contralateral ovary havenot been described in cows or mares, in women the DFaffects subordinate growth and atresia on the ispilateralovary following its selection, leading to ‘corona formation’around the DF towards the end of the follicularphase (Gore et al. 1997). Compared to women, twinovulations are frequent in mares (20%, Ginther 1992;Ginther et al. 2004a) and have recently been shown toreach similar levels in high-yielding dairy cows(Wiltbank et al. 2000). Similar to cows, follicle waveshave also been observed during the later half of theanovulatory season (Donadeu and Ginther 2002a;Watson and Al-zi’abi 2002) and during early pregnancyin mares (Ginther and Bergfelt 1992). However, theoccurrence of follicular waves during anovulatory states(such as during pregnancy or following weight loss) inwomen does not appear to have been investigated.The FSH Rise and DeclineIn all three monovulatory species, rising FSH concentrationsin systemic circulation induce the emergence ofa follicle wave which is usually detected at the time ofthe FSH peak (Austin et al. 2001; Ginther et al. 2005)(Fig. 1). Cohort attrition occurs during declining FSHconcentrations, and culminates in DF selection (cows:Adams et al. 1992; Sunderland et al. 1994; mares:Bergfelt and Ginther 1993; women: Van Santbrinket al. 1995). All growing cohort follicles contribute tothe FSH suppression, leading to a direct relationshipbetween the number of cohort follicles growing inresponse to the FSH rise and the degree of FSHsuppression (Gibbons et al. 1997; Burns et al. 2005;Ginther et al. 2005). The FSH decline causes DFselection and this has been shown functionally bypreventing the decline or elevating FSH in cows(Adams et al. 1993; Mihm et al. 1997), mares (Donadeuand Ginther 2001) and women (Schipper et al.1998; Hohmann et al. 2001). Therefore, DF selection isa systemic process simultaneously affecting cohortgrowth on both ovaries via reductions in FSH followinga transient rise. However, the incidence of transientFSH rises, the magnitude of each rise, and the lengthof the decline differ between the species. In cows,sequential FSH rises of similar magnitude as thegonadotrophin surge are associated with new folliclewaves during the luteal phase of the oestrous cycle(Adams et al. 1992; Sunderland et al. 1994), in thepost-partum period (Crowe et al. 1998; Stagg et al.1998), during pregnancy (Ginther et al. 1996) andbefore puberty (Evans et al. 1994). Functional in vivostudies showed that suppressing the first or second riseof FSH during the cycle or long-term suppression ofGnRH pulsatility will inhibit wave emergence, whichcan again be induced using exogenous FSH (Mihm andBleach 2003).Similar to cows, several transient FSH rises have beendemonstrated during the luteal phase in the mares (200–400% of basal levels), but interestingly, luteal rises arenot always associated with emergence of a follicle waveas detected by ultrasound (Gastal et al. 1997; Gintheret al. 2005). Three features are different in womencompared to cows and mares: (1) no minor or majorwaves emerge during the early to mid luteal phase(Baerwald et al. 2003); (2) very small magnitude FSHrises can induce emergence of the ovulatory waveindicating a relatively high sensitivity of the populationof small antral follicles to FSH (Baird 1987; VanSantbrink et al. 1995); and (3) DF selection occurs alsoduring the initial decline in FSH, but FSH continues todecline during the long dominance period of the DF.Thus FSH is elevated for more than 10 days in thefollicular phase (Van Santbrink et al. 1995; Baerwaldet al. 2003), which is in contrast to cows and mareswhere a final reduction of FSH to nadir levels occursjust after deviation (and this final decline is hypothesizedto induce SF1 atresia at deviation, Ginther et al. 1999;Bergfelt et al. 2001).The Follicular Secretions Oestradiol and InhibinThe FSH decline causes DF selection, and initialsuppression of FSH concentrations following the riseis contributed to the cohort follicles growing after waveemergence in all three monovulatory species (Fig. 1)(Ginther et al. 2001a). Thus, cohort secretions into thesystemic circulation must induce the decline in FSH.Cohort follicles, therefore, indirectly cause their ownatresia except for the DF which must acquire relativeFSH-independence in order to grow and differentiateduring low (cows, mares) or further declining (women)FSH concentrations. Dominant follicle secretions thencontinue to suppress FSH to prevent further waveemergence. Cohort and DFs in cows, mares and womenproduce the FSH-inhibitors oestradiol and inhibin-A(cows: Sunderland et al. 1996; Mihm et al. 1997; Bleachet al. 2001; mares: Bergfelt et al. 2001; Watson et al.2002; women: Schneyer et al. 2000; Laven and Fauser2004), and in cows and women cohort follicles produceinhibin-B (Beg et al. 2002; Laven and Fauser 2004). Inheifers and cows during growth of the first cohort of theoestrous cycle, inhibin-A increases in circulation coincidentwith small rises in systemic oestradiol reaching anÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag