Ovarian antral follicular dynamics and their relationships with endocrine variables throughout the oestrous cycle in breeds of sheep differing in prolificacy

Abstract

Transrectal ultrasonography of ovaries was performed each day in non-prolific Western white-faced (n = 12) and prolific Finn ewes (n = 7), during one oestrous cycle in the middle portion of the breeding season (October-December), to record the number and size of all follicles > or = 3 mm in diameter. Blood samples collected once a day were analysed by radioimmunoassay for concentrations of LH, FSH and oestradiol. A cycle-detection computer program was used to identify transient increases in concentrations of FSH and oestradiol in individual ewes. Follicular and hormonal data were then analysed for associations between different stages of the lifespan of the largest follicles of follicular waves, and detected fluctuations in serum concentrations of FSH and oestradiol. A follicular wave was defined as a follicle or a group of follicles that began to grow from 3 to > or = 5 mm in diameter within a 48 h period. An average of four follicular waves per ewe emerged during the interovulatory interval in both breeds of sheep studied. The last follicular wave of the oestrous cycle contained ovulatory follicles in all ewes, and the penultimate wave contained ovulatory follicles in 10% of white-faced ewes but in 57% of Finn ewes. Transient increases in serum concentrations of FSH were detected in all animals and concentrations reached peak values on days that approximated to follicle wave emergence. Follicular wave emergence was associated with the onset of transient increases in serum concentrations of oestradiol, and the end of the growth phase of the largest follicles (> or = 5 mm in diameter) was associated with peak serum concentrations of oestradiol. Serum FSH concentrations were higher in Finn than in Western white-faced ewes during the follicular phase of the cycle (P < 0.05). There were no significant differences in serum concentrations of LH between Western white-faced and Finn ewes (P > 0.05). Mean serum concentrations of oestradiol were higher in Finn compared with Western white-faced ewes (P < 0.01). It was concluded that follicular waves (follicles growing from 3 to > or = 5 mm in diameter) occurred in both prolific and non-prolific genotypes of ewes and were closely associated with increased secretion of FSH and oestradiol. The increased ovulation rate in prolific Finn ewes appeared to be due primarily to an extended period of ovulatory follicle recruitment.

Determination of the proper time for mating after oestrous synchronisation during anoestrous or oestrous by measuring electrical resistance of cervical mucus in ewes

“…Similar results have been reported in cattle (McCaughey and Patterson 1981), ewes (Bartlewski et al 1999), and buffaloes (Gupta and Purohit 2001). On the other hand, in our study and…”

“…This difference in oestradiol-17β concentrations could be related to the fact that administration of sponges for 14 days was more effective with respect to oestrus detection and pregnancy rate. It has been suggested that the diameter of ovarian follicles is a very important factor for successful ovulation (Kohno et al 2005); furthermore, the largest antral follicles are the main source of oestradiol and there are periods of increased oestradiol secretion throughout the oestrous cycle in ewes (Bartlewski et al 1999;Duggavathi et al 2006). The higher oestradiol-17β concentrations at oestrus, when sponges remain in situ for 12 days may be related to the late ovulation and lower pregnancy rate in this group, since follicle diameters could be linked with oestradiol-17β concentrations and pregnancy rates.…”

“…It is well known that vaginal resistance throughout the oestrous cycle decreases gradually in the follicular phase and reaches the lowest value in pigs (Rezac et al 2002), and sheep (Bartlewski et al 1999), during pro-oestrus, while in cattle (Aboul-Ela et al 1983), goats (Rezac et al 2001), buffaloes (Gupta and Purohit 2001), and horses (Brook 1982), the lowest resistance is during oestrus. Alterations in cervical mucus and, therefore, resistance are also known to be under the influence of oestrogens and progesterone (Rezac 2008).…”

Reproductive parameters of Santa Inês ewes submitted to short-term treatment with re-used progesterone devices

“…These data indicate that short-term protocols with progesterone, eCG and prostaglandin are sufficient to induce estrus and ovulation in ewes. The average number of ovulations we verified (1.5±0.6) are similar to those reported in Western White Face ewes (Bartlewski et al, 1999). The largest follicle diameters obtained is in accordance to Ginther et al (1995), Bartlewski et al (1999) and Evans (2003), who reported that ewe's preovulatory follicles reach maximum diameter of 5 to 7 mm.…”

“…In the present study, the use of intravaginal progesterone devices up to three times did not affect (P>0.05) the rate of ovulating animals (a total of 88.9%, 24/27), similar to the 90% also obtained in Santa Inês ewes receiving a shortterm treatment with progestagen (Cavalcanti et al, 2006). These data indicate that short-term protocols with progesterone, eCG and prostaglandin are sufficient to induce estrus and ovulation in ewes.…”