Effect of long-term hypophysectomy on ovarian follicle populations and gonadotrophin-induced adenosine cyclic 3',5'-monophosphate output by follicles from Booroola ewes with or without the F gene

Long-term (i.e. approximately 70 days) hypophysectomy led to a significant (P less than 0.05) reduction in ovarian weight but no reduction in the total number of antral follicles (greater than 0.1 mm in diameter). In hypophysectomized ++ Booroola ewes (N = 8) follicles were always less than or equal to 3 mm and in hypophysectomized FF Booroola ewes (N = 6) follicles were always less than or equal to 2 mm in diameter; in ewes of both genotypes follicles reached diameters which were approximately 40% of their predicted final size at ovulation. Under in-vitro conditions, follicles from the FF and ++ hypophysectomized ewes produced significant increases in cAMP within 1 h of exposure to gonadotrophins (P less than 0.05) although no genotypic differences in cAMP production were noted. We conclude that ovarian follicles in FF and ++ ewes have absolute requirements for pituitary hormone on reaching diameters of 2 mm and 3 mm respectively and that appreciable numbers of antral follicles in ewes of both genotypes remain responsive to pituitary gonadotrophins despite prolonged deprivation of these hormones.     

Uterine involution and ovarian changes during early post partum in autumn-lambing Corriedale ewes

The time of uterine involution and the changes in ovarian follicle populations were studied during early postpartum in multiparous, suckling Corriedale ewes lambing in the autumn. On Day 1 (n=5), Day 5 (n=4), Day 17 (n=4) and Day 30 (n=3) postpartum ewes underwent surgery to obtain ovaries and uteri. The weights of uteri and the lengths of the previous pregnant and nonpregnant horns were recorded as well as the presence of ovarian follicles larger than 1 mm in diameter. Uterine weight and length of uterine horns decreased (P2 to < 4 mm) follicles were also present. At days 17 and 30, aside from the small and medium follicles, all the ewes also had large (>/= 4 mm) follicles, and, at Day 30 2 ewes had large corpora lutea. We conclude that in autumn-lambing Corriedale ewes macroscopic uterine involution was complete around Day 17 post partum and that follicle development begins immediately after parturition, reaching preovulatory size before Day 17. In 2 of the 3 ewes studied until Day 30, ovulation (first progesterone increase) occurred after Day 17 (Days 18 and 25).     

Effects of luteinizing hormone on luteal cell populations in hypophysectomized ewes

To examine the effect of purified LH on development and function of luteal cells, 27 ewes were assigned to: (1) hypophysectomy plus 2 micrograms ovine LH given i.v. at 4-h intervals from Days 5 to 12 of the oestrous cycle (oestrus = Day 0; Group H + LH; N = 7); (2) hypophysectomy with no LH replacement (Group N-LH; N = 6); (3) control (no hypophysectomy) plus LH replacement as in Group H + LH (Group S + LH; N = 7); (4) control with no LH treatment (Group S-LH; N = 7). Blood samples were collected at 4-h intervals throughout the experiment to monitor circulating concentrations of LH, cortisol and progesterone. On Day 12 of the oestrous cycle corpora lutea were collected and luteal progesterone concentrations, unoccupied receptors for LH and number and sizes of steroidogenic and non-steroidogenic luteal cell types were determined. Corpora lutea from ewes in Group H-LH were significantly smaller (P less than 0.05), had lower concentrations of progesterone, fewer LH receptors, fewer small luteal cells and fewer non-steroidogenic cells than did corpora lutea from ewes in Group S-LH. The number of large luteal cells was unaffected by hypophysectomy, but the sizes of large luteal cells, small luteal cells and fibroblasts were reduced. LH replacement in hypophysectomized ewes maintained luteal weight and the numbers of small steroidogenic and non-steroidogenic luteal cells at levels intermediate between those observed in ewes in Groups L-LH and S-LH. In Group H + LH ewes, luteal and serum concentrations of progesterone, numbers of luteal receptors for LH, and the sizes of all types of luteal cells were maintained. Numbers of small steroidogenic and non-steroidogenic cells were also increased by LH in hypophysectomized ewes. In Exp. II, 14 ewes were assigned to: (1) sham hypophysectomy with no LH replacement therapy (Group S-LH; N = 5); (2) sham hypophysectomy with 40 micrograms ovine LH given i.v. at 4-h intervals from Day 5 to Day 12 of the oestrous cycle (Group S + LH; N = 5); and (3) hypophysectomy plus LH replacement therapy (Group H + LH; N = 4). Experimental procedures were similar to those described for Exp. I. Treatment of hypophysectomized ewes with a larger dose of LH maintained luteal weight, serum and luteal progesterone concentrations and the numbers of steroidogenic and non-steroidogenic luteal cells at control levels.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of mouse epidermal growth factor on plasma concentrations of FSH, LH and progesterone and on oestrus, ovulation and ovulation rate in merino ewes

The 24 h i.v. infusion of Merino ewes with 60 or 100 microgram mouse epidermal growth factor (EGF)/kg body weight on Days 4, 9 or 14 of the oestrous cycle decreased the strength of wool attachment and caused marked changes in subsequent reproductive performance. In ovaries removed 2 days after EGF treatment all follicles greater than or equal to 0.6 mm diameter were atretic. After 7 days either a normal pattern of atresia or no atresia was evident while after 12 days the pattern of follicular atresia was similar to that in controls. Irrespective of stage of cycle EGF caused dose-dependent increases in plasma FSH concentrations that persisted for up to 14 days. Changes in plasma LH concentrations were generally similar after infusion on Days 4 and 14, but were smaller and shorter-lived after infusion on Day 9. Irrespective of dose, the infusion of EGF on Days 4 and 14 caused immediate luteolysis then the formation of a luteinized follicle in many ewes. Most ewes treated on Day 4 returned to oestrus between Days 17 and 21 with the same ovulation rate (1.3) as the controls. Of those infused on Day 14 oestrus occurred about a cycle length later than expected and their ovulation rate then (1.9) was also similar to that of the controls (1.7). Luteal function was not affected in ewes infused on Day 9, and most returned to oestrus between Days 17 and 20 with an ovulation rate of 3.2. Fertile rams were not placed with the ewes until after the differences in ovulation rate had been observed. Mating occurred generally 2-4 weeks after treatment, and there were no differences between EGF-treated and control ewes in fertility or fecundity. The results are interpreted as indicating that mouse EGF induces ovarian follicular atresia but has differential effects on luteal function according to the stage of the oestrous cycle at which it is given. As a consequence of these two effects, which lead to differential changes in gonadotrophin secretion, ovarian function may be temporarily impaired, little affected or improved.     

Follicular populations during the estrous cycle in heifers. I. Influence of day

Ovarian follicles ⩾ 2 mm were studied in 22 Holstein heifers by daily ultrasound examinations. There were significant differences (P < 0.0001) among days of the estrous cycle for diameter of the largest and second largest follicles and in the numbers of follicles 2–3 mm, 4–6 mm, 7–10 mm, 11–13 mm, > 13 mm, and total number of follicles ⩾2 mm. Patterns of the mean profiles for all follicular endpoints except the number of follicles 4–6 mm and total number of follicles ⩾ 2 mm were bimodal. The days encompassed by the first and second portions, respectively, of the bimodal profiles were approximately: diameter of largest follicle, Days 0–14 and 15–21 (ovulation); diameter of second largest follicle, Days 0–7 and 8–20; number of follicles 2–3 mm, Days 1–11 and 12–20; number of follicles 7–10 mm, Days 0–6 and 7–18; number of follicles 11–13 mm, Days 0–8 and 9–20; and number of follicles > 13 mm, Days 2–14 and 16–21. Data for the various categories were recombined to demonstrate relationships between the numbers of follicles 2–3 mm and ⩾ 4 mm during the interovulatory interval. There were significant differences (P < 0.0001) among days in both 2–3 mm and ⩾ 4 mm follicular categories. Differences appeared due to periods of higher mean numbers of follicles 2–3 mm which began between Days 2 or 3 and Days 15 or 16 and reached maximum levels on Day 7 and Day 19, respectively. There was an inverse relationship between the number of follicles 2–3 mm vs ⩾ 4 mm and between the diameters of largest and second largest follicles. The process of selection of the follicle destined to ovulate appeared to become manifest as selective growth of the preovulatory follicle with concurrent decrease in diameter of the second largest follicle and regression of the other follicles in the various follicular categories. A similar process apparently occurred early in the interovulatory interval. There was apparently selective growth of a follicle to preovulatory size by Day 6, coincident decrease in diameter of the second largest follicle, and apparent regression of other follicles in the ultrasonically detectable pool. The only apparent difference was that the follicle which attained preovulatory diameter early in the interovulatory interval remained in the ovary for 5 or 6 days, then regressed, while the follicle which attained preovulatory diameter at approximately Day 18–20 ovulated.     

Role of intrafollicular regulators and FSH in growth and development of large antral follicles in sheep

Manipulation of circulating concentrations of hormones and ovarian follicle status was carried out on Day 11-12 of the oestrous cycle in sheep. All follicles visible on the ovary were ablated by cautery and ewes were treated with oestradiol or ovine follicular fluid (oFF) to suppress FSH or with PMSG to increase circulating gonadotrophic activity. One group underwent unilateral ovariectomy which greatly increased endogenous FSH and was the only treatment which significantly affected LH pulse frequency. The size distribution of antral follicles, the extent of atresia and the mitotic index of granulosa cells of follicles on Day 15 showed that (a) treatment with oFF inhibited the growth of follicles beyond 2 mm diameter by suppressing the mitotic index of the granulosa cells and (b) the concentration of FSH in peripheral plasma was related to the ability of small antral follicles to grow during the late luteal-early follicular phase of the cycle. Subsequently, it was demonstrated that oFF inhibits, in a dose-dependent manner, folliculogenesis sustained by PMSG in ewes on Days 12-15. Inhibition of folliculogenesis was represented by a decrease in those follicles greater than 4 mm, an increase in the relative proportion of follicles less than 2 mm, and minimal change in the average number of follicles visible on the ovarian surface, and a decrease in the mitotic index of granulosa cells of follicles less than 2 mm. There was no change in the extent of atresia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of follicular status at treatment on follicular development and ovulation in response to FSH in Spanish merino ewes

Cyclic Spanish Merino ewes were treated on Day 13 of the estrous cycle with 12 mg, i.m., FSH-P in saline (n = 9) or propylene glycol (n = 24), currently with 100 micrograms, i.m., Cloprostenol (Day 0). From Day-6 to Day 0, the ewes were observed daily by transrectal ultrasonography, after Day 0, ultrasonography was performed every 12 h for 72 h. Sizes and locations of > or = 2 mm follicles were recorded at each observation. The ovulation rate was determined by laparoscopy on Day 7 after estrus. The number of ovulations ranged from 0 to 6 in ewes treated with FSH-P in saline and from 0 to 16 in ewes receiving FSH-P in propylene glycol (P < 0.05). In the latter group, the response was bimodally distributed; about half of the females had 1 ovulation, whereas the remainder had > 4 with a mean of 7 ovulations. The ovulation rate was associated with 2 characteristics of the largest follicle present at treatment (Day 0). First, if the largest follicle on Day 0 had not changed in diameter from Day-1 to Day 0, then 7 of 9 ewes had > 3 ovulations; if the largest follicle had either increased or decreased, only 8 of 24 ewes had > 3 ovulations (P < 0.05). Second, there was a linear trend (P < 0.07) for ovulation rate to decrease as the persistence of the largest follicle at treatment increased; no ewe in which the largest follicle on Day 0 remained present for more than 36 h ovulated more than 6 follicles. As with the ovulation rate, the numbers of large follicles on Days 1.5, 2 and 2.5 varied with the interaction of change in diameter of the largest follicle on Day 0 from Day-1 to Day 0 and with vehicle. In summary, the superovulatory response was affected by the change in diameter from Day-1 to Day 0 of the largest follicle on Day 0 and the period required for that follicle to regress after treatment with FSH-P and cloprostenol.     

Use of high-resolution transrectal ultrasonography to assess changes in numbers of small ovarian antral follicles and their relationships to the emergence of follicular waves in cyclic ewes

Transrectal ovarian ultrasonographic studies have shown that, in cattle, follicular wave emergence is associated with a large increase in the number of small antral follicles (4-6mm in diameter); an analogous association has not been found for small follicles (2-3mm in diameter) in the ewe. In previous studies in ewes, accurate assessment of the number of follicles has been limited to follicles > or =2 or 3mm in size. Newer, high-resolution equipment allowed us to identify follicles > or =0.4mm and to quantify all antral follicles > or =1mm in diameter in seven cyclic Western White Face ewes. This allowed us to expand the small follicle pool examined, from 1 to 4 follicles/day (2-3.5mm in diameter) in earlier studies, to 8-18 follicles/day (1-3mm in diameter). Total number of small follicles (> or =1 and < or =3mm in diameter) increased between Days -1 and 0 (Day 0=day of ovulation), and declined between Days 1 and 3 (P<0.05). There were no significant changes in the number of small or medium (4mm in diameter) follicles around days of follicle wave emergence (+/-2 days). The 1-3 follicles in the 2-3mm size range, which constituted a follicle wave (i.e. grew to > or =5mm in size before regression or ovulation), were the only small follicles to emerge in an orderly succession during the estrous cycle, approximately every 3-5 days. Thus, unlike in cattle, there is no apparent increase in numbers of small follicles at follicle wave emergence in cyclic sheep, and little evidence for selection of recruited follicles and follicular dominance.     

The effect of recombinant GH treatment on ovarian growth and atresia in sheep

This study investigated the effect of recombinant bovine GH (rGH) on follicle development and LH secretion patterns in ewes. In Experiment 1, 20 ewes (n=10/group) synchronized with progestagen sponges on Day 0 received either a 7 d period of rGH treatment starting on Day 4, or acted as controls. On Day 11, all ewes were unilaterally ovariectomized. Follicles in the excised ovary were characterized on the basis of size, health status and rate of granulosa cell proliferation. Circulating levels of LH, GH, IGF-1 and insulin were monitored. Compared to controls, rGH treatment significantly increased the number of healthy follicles >2.0 mm, reduced the number of 0.25 to 0.5-mm follicles and reduced the number of 0.8 to 2.0-mm early atretic follicles. GH treatment also reduced the mitotic index of 0.25 to 0.5-mm follicles. Recombinant GH treatment had no effect on LH secretion patterns, but plasma GH, IGF-1 and insulin levels were increased in rGH-treated ewes. Because rGH treatment may have had an anti-atresia effect in Experiment 1, the hypothesis for Experiment 2 was that rGH treatment could maintain follicle development beyond 2.5-mm diameter in bovine follicular fluid (bFF)-treated ewes. Forty ewes (n=10/group) were synchronized with progestagen sponges. Starting 5 d after sponge insertion, ewes were treated for 6 d with rGH, bFF, rGH plus bFF, or acted as controls. On Day 12, ewes were sacrificed, and follicles were dissected out of their ovaries and assessed on the basis of size. FSH concentrations were assessed on Days 7, 9 and 11. GH treatment alone significantly increased the number of 2.5 to 4.0-mm follicles compared to controls, whereas no follicles larger than 2.5 mm were present in bFF-treated ewes. In rGH plus bFF-treated ewes, the number of 2.5 to 4.0-mm follicles was similar to controls, but there were less follicles >4.0 mm. GH treatment had no effect on FSH levels, whereas bFF treatment significantly reduced FSH levels. These results expand previous findings that rGH treatment of ewes alters follicle development, but do not suggest that rGH treatment is likely to be of benefit in superovulatory protocols. Furthermore, the data indicate that rGH has an anti-atretic action that is unlikely to be mediated via gonadotropins.     

Ultrasonographic study of ovarian function during early pregnancy and after parturition in the ewe

Transrectal ultrasonography of ovaries was performed in 11 ewes from Days 10 to 26 and on Day 30 of pregnancy to record the number, size, and position of ovarian follicles > or = 3 mm in diameter and corpora lutea (CL). Transrectal and/or transabdominal ultrasonography of the uterus was performed on Days 10 to 26, 30, 35, 40, 45 and 50 of gestation to ascertain the number and position of the conceptuses. In a second experiment, ultrasonography was conducted in 15 ewes on Days 10, 25, 30, 45 and 50 of pregnancy and from Days 13 to 29 after parturition. Ovarian data were classified into ovaries without CL (Group 1), ovaries with the CL in 1 ovary (Group 2), and ovaries with the CL in both ovaries during pregnancy (Group 3). In early pregnant ewes, the total number of follicles and the diameter of all follicles > or = 3 mm were smaller (P < 0.05) in the CL-bearing ovaries (both Group 2, n = 7 and Group 3, n = 8) than in the non-CL-bearing ovaries (Group 1, n = 7), while the largest follicle diameter was significantly smaller in Group 3 than in Group 1 or 2 ovaries. The number of 3-mm follicles in Group 2 ovaries was lower (P < 0.05) than in Group 1 or 3 ovaries, but the mean number of follicles > or = 5 mm in diameter was significantly lower in Group 3 than in Group 1. The total luteal volume per ovary was higher (P < 0.001) in Group 2 than in Group 3 ovaries of early pregnant ewes. The total follicle diameter and the number of follicles growing from 3 to > or = 5 mm in diameter was lower (P < 0.05) for Group 2 ovaries of ewes that carried twins (n = 3) compared with Group 2 ovaries from ewes with singletons (n = 4). There were no differences in follicular dynamics between Group 3 ovaries and the ovaries of Group 2 in ewes that carried twins. No follicles > 3 mm were seen in the ovaries of postpartum ewes that contained CL during gestation, until Days 21 and 25 postpartum for Groups 2 (n = 10) and 3 (n = 8), respectively, and follicles reaching > or = 5 mm in diameter were detected in only 2 ovaries (Group 2), on Days 27 and 28 postpartum, respectively. We conclude that during early pregnancy in ewes there is a suppression of antral follicle growth which appears to be exerted primarily by the developing conceptus but remains confined to CL-bearing ovaries. Residual local inhibition of follicular development extends into the postpartum period.     

The effect of subluteal levels of exogenous progesterone on follicular dynamics and endocrine patterns during early luteal phase of the ewe

Nineteen Corriedale ewes were treated with an im dose of a PGF2alpha during the luteal phase to synchronize estrus. After ovulation had been detected by using ultrasonography (Day 0); the ewes were randomly assigned to 2 different groups. In 11 ewes a CIDR, which had previously been used for 10 d, was inserted on the fourth day after ovulation. The ewes then received a dose of PGF2alpha on Day 5 to induce luteolysis. The CIDR remained in place until the end of the experiment (Day 9). Control ewes (n = 8) received no treatment. Blood samples were taken daily for estradiol, progesterone and FSH determinations. In the untreated ewes, 2 follicular waves were detected in all of the animals throughout the monitoring period, with a mean wave interval of 4.5 d. The total number of follicles which were > or =2 mm decreased from Day 0 to Day 4 (8.8+/-1.0 to 5.3+/-0.6; P< or =0.05) and then increased at Day 7 (7.5+/-0.9; P< or =0.05). The growth profiles of both the largest and the second largest follicles of Wave 1 showed significant divergence, while no divergence was observed in Wave 2. Serum estradiol concentrations decreased significantly from the day before to the day of ovulation and then increased again during the growing phase of the largest follicle of Wave 1. Concentrations of FSH were high on the day of emergence of both waves, but while a significant decline was observed after emergence in Wave 1, the levels remained high in Wave 2. In 8 of the 11 treated ewes, the largest follicle of Wave 1 was still present on the ninth day after ovulation (persistent follicle). In the other 3 ewes, the largest follicle of Wave 1 was already regressing on the day that the treatment was administered, and the largest follicle that was present on Day 9 originated from Wave 2 (nonpersistent follicle). In persistent follicle ewes, the largest follicle of Wave 1 prolonged its lifespan significantly, attaining the maximum diameter (Day 8.1+/-0.8) later than in untreated (Day 3.0+/-0.4) and nonpersisted follicle ewes (Day 2.0+/-0.6). The total number of follicles decreased in persistent follicle ewes between Day 0 and Day 4 (7.9+/-1.5 to 4.5+/-0.5, respectively; P< or =0.05) and remained low until the end of the experiment. Progesterone concentrations (nmol/L) between Days 6 and 9 were significantly different between untreated and persistent follicle ewes (12.8+/-1.0 vs. 9.4+/-1.0, P< or =0.02). The present study confirms that the largest follicle of Wave 1 is dominant in the ewe and that subluteal progesterone concentrations can prolong its lifespan and extend this dominance.     

Progestagen synchronisation in the absence of a corpus luteum results in the ovulation of a persistent follicle in cyclic ewe lambs

Progestagens are widely used to synchronise oestrous in sheep but the effects on follicular dynamics are not clear. We tested the hypothesis that when luteolysis occurs early during progestagen synchronisation prolonged growth of the ovulatory follicle will occur. Cyclic ewe lambs (40.0+/-0.3 kg) were divided into three groups: eight ewes (Long group) received a progestagen sponge (60 mg medroxyprogesterone acetate) from Days 5 to 19 after oestrous and eight ewes (Short group) received a progestagen sponge on Day 5 which was replaced on Day 10 and again on Day 15, and removed on Day 19 after oestrous. On Days 6 and 7, ewes in both groups received prostaglandin. A third group (n=5, Control) did not receive any treatment. The growth and development of follicles > or =2 mm in diameter were characterised using daily transrectal ultrasonography. On Day 18, blood samples were collected every 12 min for 8 h from five ewes in the Long and Short groups. Data were analysed by ANOVA. The maximum diameter and age (emergence to ovulation) of the ovulatory follicle was greater (P<0.01) in ewes in the Long group (7. 4+/-0.2 mm and 12.1+/-0.6 days) than in ewes in the Short group (6. 3+/-0.2 mm and 5.1+/-0.5 days) and Control group (6.3+/-0.4 mm and 6. 8+/-0.6 days). On Day 18 of the cycle, LH pulse frequency and oestradiol concentrations were greater (P<0.05) in ewes in the Long group (3.2+/-1.1 pulse per 8 h and 1.15+/-0.09 pg ml(-1)) than the Short group (0.8+/-0.4 pulses per 8 h and 0.54+/-0.08 pg ml(-1)).We suggest that the negative feedback efficacy of a long-term progestagen sponge decreased with time and led to an increase in LH pulse frequency and prolonged growth of the ovulatory follicle. We conclude that, in the absence of luteal progesterone, synchronisation with a single progestagen sponge for 14 days resulted in higher LH pulse frequency and ovulation of a persistent follicle with a larger maximum diameter, compared with controls.     

Short- and long-term effects of hypophysectomy and unilateral ovariectomy on ovarian follicular populations in sheep

The effects of hypophysectomy and unilateral ovariectomy on the total number of follicles with greater than 3 layers of granulosa cells were determined at 4 and 70 days following treatment. The population of preantral follicles (less than 0.23 min diam.) was found to be under the control of gonadotrophins but such control was only evident on a long-term basis. At 70 days after unilateral ovariectomy there was a large increase in the number of preantral follicles but at 70 days after hypophysectomy there was a large decrease. The population of antral follicles (greater than 0.23 mm diam.) was under the immediate control of gonadotrophins. By 4 days after hypophysectomy all large antral follicles had become atretic and the number of antral follicles was further decreased at 70 days after treatment. At 70 days after unilateral ovariectomy there was an increase in the number of antral follicles. The follicular growth rates at 70 days following treatment were decreased in hypophysectomized ewes but increased in ewes after unilateral ovariectomy.     

Follicular dynamics and dominance in Booroola x Finnish Landrace and Booroola x Suffolk ewes heterozygous for the F gene

To study the influence of the F gene on follicular dynamics and dominance, 2-year-old Booroola x Finnish Landrace (BFL, N = 17) and Booroola x Suffolk (BS, N = 18) ewes were compared with contemporary purebred Finn (FL, N = 18) and Suffolk (S, N = 18) ewes. In Exp. 1, oestrous cycles of ewes were synchronized during the breeding season with progestagen-impregnated sponges. At sponge removal (Day 0), 14 days after insertion, ewes of each of the 4 genetic groups were assigned to Group 1 in which all follicles visible on both ovaries were destroyed by electrocauterization except for the largest (F1) which was marked, Group 2 in which all visible follicles on both ovaries were destroyed, or Group 3 in which the 3 largest follicles of both ovaries were identified as F1, F2 and F3 and marked. At 48 h after treatment (Day 2), follicular growth was evaluated. At Day 0, the mean number of small follicles (1-3 mm) was higher (P less than 0.05) for BS, S and BFL (35.8, 35.1 and 32.9) than FL (24.9) ewes. Large follicles (greater than or equal to 4 mm) were more numerous (P less than 0.05) in FL (3.5) than in BS (2.1) ewes, BFL and S ewes being intermediate. Diameter of the F1 follicle was larger (P less than 0.05) for S (7.6 mm) than FL, BS and BFL (5.8, 5.1 and 5.1 mm) ewes. In Group 1, all F1 follicles marked at Day 0 ovulated at oestrus after sponge removal for BFL, BS and S ewes while in FL ewes, 2 of 6 F1 follicles regressed. In ewes ovulating, only the F1 follicle ovulated except for one S ewe which shed one more ovum. In Group 2, there were no follicles greater than or equal to 4 mm at Day 2 and no ewes ovulated after treatment. In Group 3, the proportion of marked follicles that ovulated was higher for S ewes than in those of the prolific genotypes. The number of follicles not marked at Day 0 but ovulating (compared to the total number of ovulations) was higher in BFL, BS and FL (8/11, 9/13 and 9/13) than S (3/10) ewes. In Exp. 2, prolific (BFL + BS) and non-prolific (S) ewes were compared following destruction of follicles greater than or equal to 3 mm with the F1 left intact (Treatment 1) or destroyed (Treatment 2), 12 days after sponge insertion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Morphological and functional characterization of large antral follicles in three breeds of sheep with different ovulation rates

Morphological and functional features of large ovarian follicles from three breeds of sheep, with different ovulation rates (Finnish Landrace N = 12, Finnish Landrace X Scottish Blackface N = 16, Merino X Scottish Blackface N = 16) were compared by integrating three techniques; ink labelling, in-vitro oestradiol production and morphological classification. The follicles were removed at two stages of the follicular phase, 1 (PG + 1) or 2 (PG + 2) days after PGF-2 alpha treatment and compared after monitoring their rates of growth with the use of ink labelling. After ovariectomy all follicles greater than or equal to 1 mm in diameter were dissected, and the 8 largest were incubated individually for 2 h to assess their ability to secrete oestradiol and testosterone. After incubation the follicles were processed for histological examination and checked for atresia. An analysis of the follicle population was based on in-vitro oestradiol secretion rates in all three breeds; an oestrogen-active population producing 500-8100 pg oestradiol/ml/h and an oestrogen-inactive population producing 0-499 pg oestradiol/ml/h. A comparison of the 3 approaches demonstrated agreement on 94.3 +/- 1.2% of occasions. Ink-labelling demonstrated that all follicles identified as oestrogen-active were increasing in size. Within oestrogen-active follicles significant correlations were detected between oestradiol production and testosterone production (r = 0.42), oestradiol production and granulosa cell number (r = 0.45) and between oestradiol production and mitotic index (r = -0.38). A regression model fitting breed, stage of atresia, granulosa cell number, in-vitro testosterone production and mitotic index demonstrated that granulosa cell number is a characteristic which contributes significantly to the variation of in-vitro oestradiol production in oestrogen-active and oestrogen-inactive follicles. There was no significant difference between breeds in the mean number of ink-labelled follicles growing from Day PG - 1 to Day PG + 1. There was a significant difference between the breeds in the number of ink-labelled follicles growing between Days PG + 1 and PG + 2 (Days 1 and 2 of the follicular phase), the number being similar to the ovulation rate for the breed. The majority of the oestrogen-active follicles had been recruited by Day PG - 1, although in the Finnish Landrace genotypes more than 30% were recruited on or after Day PG + 1 compared to less than 10% in Merino x Scottish Blackface ewes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Changes in morphological appearance and functional capacity of recruited follicles in cows treated with FSH in the presence or absence of a dominant follicle

This study was designed to determine the effect of the presence of a dominant follicle at the beginning of FSH stimulation on the morphological appearance and functional capacity of recruited follicles during FSH stimulation in cattle. Synchronized nonlactating dairy cows were assigned to 1 of 2 groups and treated with FSH in the presence (n = 5) or absence (n = 6) of a dominant follicle between Days 7 and 12 of the estrous cycle (Day 0 = estrus) to stimulate follicular growth. Dominant follicles were identified by daily ultrasonographic observations, beginning on Day 3 of the estrous cycle. Dominant follicle had an ultrasonographic diameter > or = 10 mm and were in a growing phase, or maintaining a constant diameter (> or = 10 mm) for less than 4 d. Ovaries were collected at slaughter on the morning of the third day following initiation of the FSH stimulation. All follicles > 2 mm were dissected, classified according to diameter (Class 1: 2 to 4.4 mm; Class 2: 4.5 to 7.9 mm; Class 3: > 8 mm), and incubated individually for 90 min in medium M-199 (37 degrees C, 5% CO2). Following incubation, integrity of each follicle was evaluated histologically to assess the level of atresia and biochemically to determine the in vitro release of estradiol (E2) and androstenedione in culture media. On Day 3 of the FSH treatment, mean number of follicles in each class was similar (P > 0.1) between the 2 groups. The percentage of atretic follicles in Classes 1 and 3 on Day 3 of the FSH stimulation did not differ (P > 0.1) between the 2 groups. However, the percentage of atretic follicles in Class 2 was higher (P < 0.005) in cows treated with FSH in presence than in absence of a dominant follicle (60.8 vs 38.2%). The release of E2 in culture media by small Class 1 atretic or healthy follicles, by Class 2 atretic and by Class 3 healthy follicles was not affected (P > 0.1) by the ovarian status. However (P < 0.001), the release of E2 in culture media of Class 2 healthy and Class 3 atretic follicles was less for follicles harvested from cows bearing than from those not bearing a dominant follicle. Within each follicular class, concentrations of androstenedione in the culture media did not differ between the 2 groups (P > 0.1). These results suggest that the presence of a dominant follicle at the beginning of FSH stimulation alters the population of follicles recruited FSH stimulation. This may be associated with the reported decrease of the superovulatory response in cows superovulated in presence of a dominant follicle.     

Comparison of the total ovarian follicular populations at day 140 of pregnancy and at day 5 postpartum in ewes

The total ovarian follicular populations were determined in ewes at Day 140 of pregnancy and at Day 5 postpartum. The right and left ovaries of five pregnant and five non-suckling ewes of the Préalpes-du-Sud breed were used in this study. All the ovaries were serially sectioned at a thickness of 7 μm, and every section was examined microscopically.The mean numbers of preantral follicles per ovary increased (P<0.005) at Day 5 postapartum as compared to Day 140 of pregnancy. The distribution of preantral non-atretic follicles into different size classes clearly showed a sharp increase in the mean number of follicles per size class at Day 5 postpartum, especially those leaving the reserve of primordial follicles.No difference was detected between both groups of ewes in the mean number of antral follicles. The diameter of the largest antral follicle at Day 140 of pregnancy does not exceed 1.5 mm. However, at Day 5 postpartum, a population of large follicles ≥ 1.5 mm was observed, reaching 2–4 mm in diameter.We conclude that although the pattern of normal follicular development is inhibited during late pregnancy, the ovary at this time is not quiescent, and ovarian follicular development starts well before parturition. The increasing number of preantral follicles, as well as the enlargement of antral follicle diameter observed at Day 5 postpartum, may be correlated with increasing secretion of FSH after lambing.     

Mammary gland development and alpha-lactalbumin production in hypophysectomized, pregnant mice

Swiss Webster mice were hypophysectomized on Day 10 of pregnancy and the effect of the ablation on mammary gland development was estimated by measuring the total weight and the DNA, RNA, and alpha-lactalbumin contents and concentrations of the mammary gland on Days 14 and 18 of gestation. Although a significant increase in mammary gland weight occurred in the hypophysectomized animals between Days 10 and 18 of pregnancy, the mammary gland weight of the hypophysectomized mice was significantly reduced when compared with intact and sham-operated mice on both Days 14 and 18 of pregnancy. The total RNA content of the mammary gland was also reduced in the hypophysectomized mice, although it increased significantly from Day 10 to Day 18. The alpha-lactalbumin content of the mammary gland increased only slightly between Days 10 and 14 of gestation in the intact and sham-operated mice, but a large increase was found on Day 18 in both groups. There was, on the other hand, no increment in the alpha-lactalbumin content of the mammary gland in the hypophysectomized mice either on Day 14 or 18 of gestation. The DNA content of the mammary gland was not affected by hypophysectomy when estimated on Days 14 and 18 of pregnancy. The effects of hypophysectomy on the concentrations of mouse placental lactogen II (mPL-II), progesterone, corticosterone, and thyroxine in the maternal serum were also assessed. The concentration of mPL-II was significantly elevated in the hypophysectomized mice, whereas the circulating concentrations of both corticosterone and thyroxine were greatly reduced. The serum progesterone concentration was not significantly altered by hypophysectomy. (ABSTRACT TRUNCATED AT 250 WORDS)     

Associations between emergence of follicular waves and fluctuations in FSH concentrations during the estrous cycle in ewes

Folliculogenesis was studied daily in 16 interovulatory intervals in 5 Polypay ewes from mid February through April using transrectal ultrasonic imaging. The 3-mm follicles attaining > or = 5 mm on Days--1 (ovulation=Day 0) to 11 showed significant peak numbers on Days 0, 5 and 10. The number of 3- and 4-mm follicles that did not reach > 4 mm was not significant, indicating that these follicles did not manifest a wave pattern. A follicular wave was defined as one or more follicles growing to > or = 5 mm; the day the follicles were 3 mm was the day of wave emergence, and the first wave after ovulation was Wave 1. Waves 1, 2 and 3 emerged on Days -1 to 2,4 to 7 and 8 to 10, respectively. Four interovulatory intervals in April were short (9 to 14 d), indicating the end of the ovulatory season. In the remaining 12 intervals, the ovulatory wave was Wave 3 in one interval, Wave 4 in 8 intervals, and Wave 5 or 6 in 3 intervals. The ovulatory wave followed the rhythmic pattern of Waves 1 to 3 by emerging on Days 11 to 14 in 50% of the intervals. In the remaining intervals, either the ovulatory wave was Wave 4 but did not emerge until Day 16 or other waves intervened between Wave 3 and the ovulatory wave. The longest intervals (22, 24 and 24 d) had >4 waves. Based on a cycle-detection program, peak values of FSH fluctuations were temporally associated with the emergence of waves as indicated by the following: 1) tendency (P < 0.08) for an increase in FSH concentrations between 3 and 2 days before emergence of a wave; 2) close agreement between mean number of waves per interval (mean +/- SEM, 4.1 +/- 0.3) and mean number of identified FSH fluctuations (4.5 +/- 0.3); 3) close agreement in length of interwave intervals (4.0 +/- 0.3) and interpeak (FSH) intervals (3.6 +/- 0.2); 4) positive correlation (r(2)=0.8) for number of the 2 events (follicular waves and FSH fluctuations) within intervals; and 5) a closer (P < 0.01) temporal relationship between the 2 events than would have been expected if the events were independent. The results support a relationship between transient increases in FSH concentrations and emergence of follicular waves throughout the interovulatory interval in Polypay ewes, with the 2 events occurring approximately every 4 d.     

Failure of the LH-releasing hormone agonist, deslorelin, to prevent development of a persistent follicle in heifers synchronized with norgestomet

The use of exogenous progestagens for estrus synchronization in cattle can result in a persistent dominant follicle which is associated with reduced fertility. We examined whether the LHRH agonist, deslorelin, would prevent the formation of a persistent follicle in heifers synchronized with norgestomet. The estrous cycles of heifers were synchronized with cloprostenol, and on Day 7 of the ensuing cycle the heifers received one of the following treatments for 10 d: Group C (n = 5), untreated control; Group N (n = 6), injection of a luteolytic dose of cloprostenol on Days 7 and 8 and implant of norgestomet from Day 7 to Day 17 (i.e. typical 10-day norgestomet implant period); Group D (n = 6), injection of cloprostenol on Days 7 and 8 and implants of deslorelin from Day 7 to Day 17; Group ND (n = 6), injections of cloprostenol and both norgestomet and deslorelin implants as above. Follicle growth was monitored using ultrasonography. Group-N heifers showed continued follicle growth and had larger follicles on Day 17 of the cycle than Group-C heifers (16.8 +/- 1.6 and 10.4 +/- 1.6 mm). Follicle growth for Group-D and ND heifers was similar and variable, and seemed to depend on follicle status at the initiation of treatment. Heifers with follicles of 5 to 10 mm (n = 9) in diameter either showed no follicle growth (2 9 ) or developed large follicles (7 9 ), while heifers with follicles approximately 12 mm (n = 3) in diameter showed follicle atresia with no further significant growth. On Day 17, size of the largest follicle was similar for Group-ND (14.3 +/- 2.9) and Group-D (16.8 +/- 1.6) heifers. Heifers in Group N showed estrous behavior 1.8 +/- 0.2 d after treatment, whereas heifers in Groups D and ND did not show estrus for 2 to 4 wk. The results show that combined treatment with progestagen and an LHRH agonist does not consistently prevent the development of a persistent dominant follicle and that return to estrus can be delayed after treatment with an LHRH agonist.