Follicle size and reproductive hormone profiles during a post-weaning altrenogest treatment in primiparous sows.

This study investigated the endocrine background of follicle size changes during post-weaning altrenogest treatment. altrenogest-treated sows received a 20-mg dosage daily at 8.00 a.m. from Day -1 to Day 14 after weaning. On Day -1, only 3/13 altrenogest-treated sows showed LH pulses compared with 8/8 control sows (P=0.001). On Day 0, control sows showed a typical high frequency-low amplitude LH pattern, indicative for recruitment of oestrogenic follicles. In altrenogest-treated animals on Day 0, half of the sows showed high frequency-high amplitude pulses from 4-5h after weaning. In altrenogest-treated sows, average follicle size increased from 3.1±0.5 mm on Day 0 to 4.4±0.6mm on Day 5, then decreased to 3.7±0.5 mm on Day 7 and stabilised thereafter. FSH and oestradiol (E2) concentrations showed a distinct diurnal pattern; high at 7.00 a.m. and low at 3.00 p.m. E2 concentrations (7.00 a.m.) showed a 2.5-fold increase from Day -1 to Day 2, and subsequently a 2-fold decline to reach a plateau at Day 8. FSH concentrations reached maximum levels by Day 5 and slowly declined afterwards. In conclusion, once-daily administration of altrenogest starting one day before weaning delays the weaning-induced increase in LH pulses. Although FSH and follicle size increase until Day 5 after weaning, follicle E2 production already decreased from Day 2 after weaning. Post-weaning altrenogest treatment thus results in a follicular wave of follicles that lose oestrogenic competence at Day 2 after weaning, presumably related to the changed LH dynamics during altrenogest treatment.

The induction of a secondary corpus luteum on day 12 post-ovulation can delay the time of luteolysis in high-producing Holstein cows.

Luteolysis before the time of maternal recognition of pregnancy is one cause of low fertility in high-producing dairy cows. The objective of this study was to assess whether induction of a secondary corpus luteum (CL) late in the luteal phase would delay the time of luteolysis. Twenty high-producing Holstein cows were synchronized to ovulation (Day 0) with the Ovsynch protocol and received hCG (1500 IU im) on Day 12. Corpora lutea formation (as evaluated by ultrasonography) and plasma P4 concentrations were monitored from Days 4 to 36. hCG treatment induced the formation of one secondary CL (CL2) in 11 of 20 cows (55%) from the dominant follicle (mean diameter: 14.2 ± 0.9 mm) of two-wave (3/11) and three-wave (8/11) cycles. The maximal diameter of the CL2 (23.3 ± 1.9 mm) was reached approximately 6 days after hCG treatment and was correlated with its structural lifespan (p < 0.01). Cows that formed a CL2 after hCG had higher mean plasma P4 concentrations on Day 14 (+4.5 ng/ml) and Day 18 (+3.0 ng/ml) compared with cows without CL2 (p < 0.05). The structural regression of CL2 begun approximately 8 days after that of the CL1, and the median time at which the first drop in circulating P4 levels occurred was later in cows that formed a CL2 than in those that did not (Day 26 vs Day 18; p < 0.01). Thus, the induction of a CL2 by hCG on Day 12 might reduce the risk of premature luteolysis in high-producing dairy cows after insemination.

Regulation of folliculogenesis and the determination of ovulation rate in ruminants.

The paper presents an update of our 1993 model of ovarian follicular development in ruminants, based on knowledge gained from the past 15 years of research. The model addresses the sequence of events from follicular formation in fetal life, through the successive waves of follicular growth and atresia, culminating with the emergence of ovulatory follicles during reproductive cycles. The original concept of five developmental classes of follicles, defined primarily by their responses to gonadotrophins, is retained: primordial, committed, gonadotrophin-responsive, gonadotrophin-dependent and ovulatory follicles. The updated model has more extensive integration of the morphological, molecular and cellular events during folliculogenesis with systemic events in the whole animal. It also incorporates knowledge on factors that influence oocyte quality and the critical roles of the oocyte in regulating follicular development and ovulation rate. The original hypothetical mechanisms determining ovulation rate are retained but with some refinements; the enhanced viability of gonadotrophin-dependent follicles and increases in the number of gonadotrophin-responsive follicles by increases in the throughput of follicles to this stage of growth. Finally, we reexamine how these two mechanisms, which are thought not to be mutually exclusive, appear to account for most of the known genetic and environmental effects on ovulation rate.

Reproductive features and faecal progesterone metabolite profile in female ferrets.

Elevated post-partum progesterone metabolite (P(4) -met) levels have been recently postulated to occur in lactating lynxes. The aims of this study were to monitor reproductive features in female ferrets, changes in the faecal P(4) -met concentrations throughout the breeding season and ovarian activity in post-partum lactating and non-lactating (NL) female ferrets. Our results indicate that coinciding with the results described in the lynx, elevated faecal P4-met concentrations occur in lactating ferrets, furthermore, that the duration of elevated secretion of P(4) seems to be dependent on the duration of lactation (P4-met at delivery, n=47: <500 ng/g; 5-7 days after delivery, during lactation, n=47: ≥ 500-800 ng/g; in females weaned at delivery, n=4: baseline levels). Three days after ovariohysterectomy of lactating females, P(4) -met concentrations decreased to baseline levels. In lactating females, the ovarian stroma is more active than that in NL ones implicating that the ovary is at least in part responsible for the elevated P4-met concentrations. Ovaries of lactating females contained many luteinized cells either as luteinized granulose cells in the wall of late pre-antral/early antral follicles or as corpus luteum (CL)-like structures. Early resumption of the entire ovarian activity (developed follicles and oestrus) occurs in NL post-partum females, while final follicular development is blocked (follicles stalls at antral stage) in the lactating ones (however, occasionally lactational oestrus may occur). We suppose that the elevated faecal P4-met during lactation together with suckling and other hormonal effects may contribute to prevention of early returning to oestrus in nursing female ferrets.

Effect of hCG on early luteal serum progesterone concentrations in PG600-treated gilts.

Gilt oestrus and ovulation responses to injection of a combination of equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG) (PG600) can be unpredictable, possibly reflecting inadequate circulating LH activity. The objective of this study was to determine the effect of PG600 followed by supplemental hCG on gilt ovarian responses. In experiment 1, 212 Hypor gilts (160 day of age) housed on two farms in Spain received intramuscular (i.m.) injections of PG600 (n = 47), or PG600 with an additional 200 IU hCG injected either concurrently (hCG-0; n = 39), or at 24 h (hCG-24; n = 41) or 48 h (hCG-48; n = 45) after PG600. A further 40 gilts served as non-injected controls. Ovulation responses were determined on the basis of initial blood progesterone concentrations being <1 ng/ml and achieving >5 ng / ml 10 d after the PG600 injection. The incidence of ovulating gilts having progesterone concentrations >30 ng/ml were recorded. During the study period, 10% of control gilts ovulated whereas 85-100% of hormone-treated gilts ovulated. There were no significant differences among hormone groups for proportions of gilts ovulating. The proportions of gilts having circulating progesterone concentrations >30 ng/ml were increased (p < or = 0.02) in all hCG treated groups compared with the PG600 group. In experiment 2, a total of 76 Hypor gilts at either 150 or 200 days of age were injected with PG600 (n = 18), 400 IU eCG followed by 200 IU hCG 24 h later (n = 20), PG600 followed by 100 IU hCG 24 h later (n = 17), or 400 IU eCG followed by 300 IU hCG 24 h later (n = 21). Blood samples were obtained 10 days later for progesterone assay. There were no effects of treatment or age on incidence of ovulation, but fewer 150-day-old gilts treated with PG600 or 400 IU eCG followed by 200 IU hCG had progesterone concentrations >30 ng / ml. We conclude that hCG treatment subsequent to PG600 treatment will generate a higher circulating progesterone concentration, although the effect is not evident in older, presumably peripubertal, gilts. The mechanism involved and implications for fertility remain to be determined.

Reversible downregulation of endocrine and germinative testicular function (hormonal castration) in the dog with the GnRH-agonist azagly-nafarelin as a removable implant "Gonazon"; a preclinical trial.

Downregulation of anterior pituitary GnRH-receptors by application of a slow release GnRH-implant offers an effective and reversible alternative to surgical castration of the male dog. Aim of the present study was to test the efficacy and the underlying mechanisms of a new non-biodegradable controlled-release device implant (Gonazon((R)), Intervet, containing 18.5mg of the GnRH-agonist Azagly-Nafarelin). Eight male beagle dogs were implanted s.c. at the para-umbilical region. In four dogs implant removal was after 180 days (group 1), in the other four dogs after 365 days (group 2). Eleven weeks after implantation availability of LH was reduced (p<0.0001) by 70%. After an initial increase lasting for about 4 days, testosterone (T) and estradiol (E2) concentrations decreased (p<0.0001) to basal levels within 17.5+/-8.4 days. Size of testes was decreased by about 82% after 17 weeks, size of prostate by about 46% after 5 weeks (p<0.0001). Five to 7 weeks after implantation all dogs were aspermic. Testosterone and estradiol concentrations, together with testicular and prostatic size remained suppressed in all dogs in group 1 and one dog of group 2 until implant removal. The other three dogs of group 2 escaped from down-regulation between 223 and 324 days. Effects on the availability of LH, T, E2 and on testicular and prostatic size were fully reversible after implant removal or escape from down-regulation. In six dogs semen quality was back to pre-treatment values after about 29 weeks, however, one dog developed oligozoospermia while another one stayed azoospermic, probably due to an obstruction within the epididymal duct.

Controlled delivery of a GnRH agonist by a silastic implant (Gonazon) results in long-term contraception in queens.

Many female cats are spayed to prevent problems associated with calling and unwanted pregnancies. This study describes the safety and efficacy of an alternative approach, using an azagly-nafarelin containing implant (Gonazon) inserted subcutaneously in the neck of six treated queens for 3 years. These six queens together with six controls were permanently housed with vasectomized tom cats, and changes in progesterone concentrations were used to document the contraceptive efficacy of Gonazon. All six control queens ovulated regularly throughout the treatment period (3 years), as shown by regular changes in progesterone concentration. Sixteen ovulatory cycles were observed in each control throughout the study. In Gonazon treated queens, during the week following implant placement, two queens displayed a treatment-induced rise in progesterone concentration. Later on, all treated queens continuously displayed low progesterone concentrations until 3 years post-implant insertion, with the exception of a single isolated episode (at approximately 2.5 years of treatment), of follicular luteinization in two queens. In all queens, azagly-nafarelin concentrations peaked in the week following implant insertion remained high for 1 month and later decreased slowly. After 2.5 years of treatment, azagly-nafarelin concentrations were still greater than 150 pg/ml in 3/6 queens. During a 6-month long extension of the study (36-42 months post-treatment), all queens (treated and controls) were run with intact tom cats. None of them conceived. Following autopsy, ovarian weight and diameter of the uterine horns of 3/6 treated queens were shown to be similar to those of the controls. In conclusion, this study demonstrated that Gonazon efficiently prevented ovulation in queens (100%) for 3 years. Return to fertile heat was not observed towards the end of treatment. However, in half of the treated queens, reversibility of the treatment induced effects on the genital tract was demonstrated.

Ovsynch synchronization and fixed-time insemination in goats.

This study assessed the efficacy of an Ovsynch protocol (vs. the classical cronolone containing vaginal sponge+eCG treatment) to generate fixed-time insemination in goats during the breeding season. Each regimen was applied to 24 Boer goat does. Onset and duration of estrus were determined with an aproned male and follicular development was monitored by ultrasonography. Ovulation and quality of the corpora lutea were established from progesterone concentrations. In 10-11 goats per group, LH concentrations were determined throughout the preovulatory period. Does were inseminated at pre-determined times (16 h after the second GnRH injection and 43 h after sponge removal). Estrus was identified in 96% of the Ovsynch-treated goats (at 49 h after prostaglandin injection) and in 100% of the goats synchronized with sponges (at 37 h after sponge removal). Low progesterone concentrations at the time of AI were observed in 21/24 and 24/24 goats synchronized by Ovsynch and sponges, respectively. Synchronization of the LH surge was tighter following Ovsynch compared to sponge treatment. Kidding rates (at 58 and 46% in the Ovsynch and sponge groups, respectively) and prolificacy (at 1.86 and 1.83 in the Ovsynch- and sponge-treated goats) were similar for both groups, as were the number of ovulations (2.9 and 3.3) and the proportion of does with premature corpus luteum regression (29 and 17%). When excluding does with premature luteal regression and those with low progesterone levels when receiving prostaglandins, kidding rate reached 87.5% (14/16) after Ovsynch. During the breeding season, the Ovsynch protocol may thus be an useful alternative to the sponge-eCG treatment.

Treatment with a subcutaneous GnRH agonist containing controlled release device reversibly prevents puberty in bitches.

In most species, continuous administration of GnRH agonists desensitizes the pituitary to GnRH, and blocks ovarian function. The aim of this study was to assess the effects of a novel controlled release device containing azagly-nafarelin (Gonazon) to prevent puberty in young Beagle bitches (mean age: 4.88 +/- 0.32 months). Gonazon containing 18.5 mg azagly-nafarelin (n = 10) or a placebo implant (n = 10) was administered subcutaneously. Throughout the 1-year treatment, estrus behaviour was monitored weekly. Plasma progesterone concentrations, as well as body weight and height, were measured monthly. Following implant removal, estrus detection and progesterone measurement were continued until occurrence of puberty in all bitches. Control bitches displayed puberty (estrus, followed by ovulation) at approximately 11.9 +/- 2.7 (range, 8-16) months of age. In contrast, none of the Gonazon treated bitches displayed puberty during the period when Gonazon was present. Following removal of Gonazon, resumption of estrus and ovulation naturally occurred (seven bitches) or was induced (three bitches) approximately 8.5 (1.2-14.3) months later. As a consequence, age of puberty of the Gonazon treated bitches was 25.5 +/- 5 (18-31) months. No clinically detectable side effects were noted in Gonazon treated bitches. Height at withers was unaffected by treatment. Changes in body weight with time were also unaffected by treatment. Implants were well tolerated and generally easy to remove. These data demonstrated that Gonazon safely, efficiently and reversibly prevents reproductive function for 1 year in prepubertal bitches.

Multiple pituitary and ovarian defects in Krox-24 (NGFI-A, Egr-1)-targeted mice.

The zinc finger transcription factor Krox-24 (NGFI-A, Egr-1) is encoded by an immediate-early serum response gene expressed in various physiological situations and tissues. To investigate its function, we have created a null allele. Mice homozygous for the mutation have a reduced body size, and both males and females are sterile. These phenotypes were related to defects in the anterior pituitary of both sexes and in the ovary. In the pituitary, two cell lineages expressing Krox-24 are differentially affected by the mutation: somatotropes present abnormal cytological features and are reduced in number, consistent with the decreased GH content observed in these animals; in contrast gonadotropes are normal in number, but specifically fail to synthesize the beta-subunit of LH. In the ovary, LH receptor expression is prevented, indicating an involvement of Krox-24 at two levels at least of the pituitary-gonadal axis. Our data, together with the results of a previous report describing another Krox-24 mutant allele, suggest that Krox-24 may have two distinct molecular functions in the anterior pituitary: transcriptional activation of the LHbeta gene in gonadotropes and control of cell proliferation and/or survival in somatotropes by unknown mechanisms.

Comparison of cellular distribution of LH receptors and steroidogenic enzymes in the porcine ovary.

Previous studies have shown a heterogeneous expression of LH receptors in various structures of the porcine ovary. Specially striking was the existence in the preovulatory follicle of inner layers of theca interna cells devoid of LH receptor and the confinement in the corpus luteum of the LH receptor to the external cellular layers. In the present study, we have compared the steroidogenic capabilities of LH receptor-positive and -negative cells using immunocytochemistry for side-chain cleavage P450, 3 beta-hydroxysteroid-dehydrogenase, 17 alpha-hydroxylase P450 and aromatase P450. We have also examined, using the same methods, the evolution of the various cell types after ovulation and during the development of the corpus luteum. In preovulatory follicles the inner layers of theca cells which were not labelled with anti-LH receptor antibodies appeared to express the steroidogenic enzymes in a way similar to that of the outer LH receptor-positive cell layers. Ovulation per se did not change the distribution of LH receptors (present in the outer luteal cells and in the granulosa) or of steroidogenic enzymes. However, 48 h after follicular rupture there as a marked decrease in overall labelling with anti-LH receptor antibody, and especially a disappearance of immunostaining in the luteal cells of granulosa origin. In the mid-luteal phase (6 days after ovulation), the receptor content seemed to increase in the peripheral luteal cells derived from the theca but the receptor did not reappear in the granulosa-derived luteal cells. Thus the down-regulation of LH receptor appeared to be reversible in the external thecal layers but irreversible in the granulosa cells. Furthermore, the distribution of the various steroidogenic enzymes in the corpora lutea delineated granulosa-derived from theca-derived cells and showed that only the external layers of the latter expressed the LH receptor. These results showed the existence in the preovulatory follicle of two theca interna regions expressing the same steroidogenic enzymes but possibly submitted to a different hormonal control. Furthermore, the cells derived from these two regions as well as the cells of granulosa origin showed a distinct pattern of variation of LH receptivity during the development of the corpus luteum. During these studies we also observed that, in the interstitial tissue, only a minority of cells which derived from remnants of atretic follicles expressed both the LH receptor and the steroidogenic enzymes.

Oocyte attrition.

During oogenesis, germ cell numbers sharply decrease when meiosis is initiated. There is solid evidence (DNA ladders, in situ detection) that this loss is through apoptosis. Oocyte apoptosis appears to hit mitotic primordial germ cells (PGC), pachytene oocytes and early primordial follicles. The control of oocyte apoptosis is not fully understood, although survival factors (LIF, kit ligand and FGF), as well as death inducing factors (fas ligand, TGFbeta), have been identified. Fas ligand binding on oocytic fas may result in caspase 8 activation. Two pathways inducing oocyte apoptosis may then be operating. In the first one, activated caspase 8 will induce activation of executioner caspases. In the second one, activated caspase 8 will trigger the cleavage of the bcl(2) family member Bid, which will act on mitochondria, resulting in cytochrome c release, caspase 9 activation and finally, activation of all executioner caspases. As a consequence of caspase activation, alterations in the cell nucleus (DNAse activation, PARP fragmentation), in the cell cytoskeleton (lamin) and cell metabolism will occur, producing cell death. During folliculogenesis, germ cell loss, owing to oocyte apoptosis, has been postulated within primordial and preantral follicles. Its regulatory mechanisms may be even more complex than those operating in foetal oocytes since additional control factors include EGF/TGFalpha and bcl(2) (survival) and activin (death inducer). In contrast, oocytes from antral follicles appear to be very unsensitive to death inducing stimuli.

Ovarian morphology and function in 12-week-old lambs from breeds with different ovulation rates as adults.

Follicular development and function were compared in 12-16-week-old Romanov and non-prolific (Ile-de-France or Prealpes) lambs. At 12 weeks of age, there was no difference between breeds in the population of antral follicles, their size distribution, their atresia, or the size of the largest follicles. Whatever the breed, intact follicles explanted from 12-week-old lambs actively produced testosterone in an unsupplemented medium. This production increased in a gonadotrophin-supplemented medium. In contrast, basal oestradiol production by Romanov follicles was reduced compared with Ile-de-France and Prealpes follicles. However, in both breeds this production increased about two-fold in an FSH-supplemented medium. At 14-16 weeks of age, lambs of both breeds had LH-sensitive follicles, as evidenced by their ability to ovulate following the injection of hCG. The number of such follicles was related to the prolificacy of the lambs (Romanov 2.8, Ile-de-France 1.6). Hence, at 12-16 weeks of age, the maturation of the ovary is not fully completed in Romanov lambs. Acquisition of a fully functional aromatase system and maturation of the central nervous system are probably required for puberty to proceed. Their relative timings may differ between breeds.

Relationships between follicle-stimulating hormone, follicle growth and ovulation rate in sheep.

The changes in follicle-stimulating hormone (FSH) concentration required to affect follicle growth and ovulation rate within individual ewes were examined. Relationships between peripheral FSH concentrations during the late-luteal and follicular phase and subsequent ovulation rates were investigated in 22 ewes from 4 breeds over 3 successive cycles (Experiment 1). Ewes were grouped as follows: Group 1 (n = 6), ewes exhibiting the same ovulation rate at each oestrous cycle: Group 2 (n = 5), ewes with three different ovulation rates at each oestrous cycle; and Group 3 (n = 11), ewes with the same ovulation rate at two oestrous cycles and a different ovulation rate on one occasion. Data from ewes in Group 1 and 3 provided estimates on the variation in FSH concentrations between cycles which were not large enough to alter ovulation rate (range, 0-67% variation in FSH concentration). In Group-2 ewes, there was no consistent association between increases in ovulation rate and the proportional increases in FSH concentrations. Differences in FSH concentrations were often less than those that did not alter ovulation rate in Group-I ewes. Furthermore, only 3 of 11 Group-3 ewes demonstrated high FSH concentrations associated with high ovulation rate (or low FSH concentrations and low ovulation rate) when compared with the concentrations found at the two cycles in which ovulation rate was similar. Hence, there was little evidence that FSH concentrations during the late-luteal and follicular phase are associated with changes in ovulation rate within individual ewes. In Experiment 2, follicles of similar size obtained from the same ewe (FecBFec+ and Romanov) showed markedly different responses in vitro to graded doses of FSH as measured by aromatase activity. It is concluded that, within a ewe, the large variability between gonadotrophin-dependent follicles in their requirement for FSH prevented the expression of any thresholds of ovarian response to FSH.

Aromatase activity of ovine follicular walls: technical validation and physiological control.

Since aromatase activity quickly disappears in cultured sheep granulosa cells, its control is poorly understood. As a result, an aromatase assay was developed using cultures of follicular walls and measuring the amount of 3H2O generated from 3H-testosterone. Chromatography and mass spectrometry analysis demonstrated that 3H2O production was indeed associated with the production of oestradiol-17 beta. Optimization of the assay demonstrated: (1) a steady increase in the amount of 3H2O produced over at least 12 h; and (2) highly significant correlations between the amounts of 3H2O measured and the weight of the follicular wall or the amount of 3H-testosterone provided. Furthermore, a highly significant correlation (r = 0.82) was observed between the amount of 3H2O produced and the concentration of oestradiol in the same samples. The effects of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and oestradiol on aromatization by follicles at two specific stages of maturation (recruitment, 12 h after luteolysis; dominance, 36 h after luteolysis) were then assessed. At recruitment and dominance, FSH was able to modulate aromatase activity similarly, increasing and decreasing the activity at low concentrations and high concentrations respectively. At recruitment and dominance, oestradiol had no stimulatory effect on basal aromatase activity and even blocked the stimulatory effects of FSH on aromatase at recruitment. LH significantly inhibited the FSH-stimulated aromatase activity of dominant follicles. It is concluded that: (1) FSH may induce the recruitment of follicles by increasing aromatase activity; and (2) neither oestradiol nor LH stimulate the aromatase activity of follicles which could explain maintenance of the dominant follicle.

Ovine follicular fluid inhibits aromatase activity.

"Within follicle" regulations may be important for the fine tuning of gonadotrophin action in ovarian follicles. While numerous growth factors, steroids or proteins which are present in follicular fluid have been shown to have the ability of positively or negatively affecting follicle function, the net effect of follicular fluid of the dominant follicle on its function is unclear.A bioassay measuring aromatase activity of follicular walls was used (1) to check whether follicular fluid from dominant follicles can alter aromatase activity (2), to check how follicle size, atresia and specific gonadotrophins alter the effects of follicular fluid (3), to identify the nature (steroid or protein) of the active compound(s), and (4) to check whether the inhibition is specific of aromatase. Dominant follicular fluid had the ability to reduce aromatase activity. This effect was dose dependent and was obvious whether or not a protease inhibitor was added to the incubation medium. There was no difference in the magnitude of the inhibitory effect of follicular fluid when FSH (2 ng/ml) or no FSH was added to the incubation medium. LH, however, could potentialise the inhibitory effects of follicular fluid. Dominant follicular fluid was more potent to inhibit aromatase than follicular fluid from atretic follicles. Medium conditioned by granulosa cells, but not by theca cells could inhibit aromatase activity when added to the incubation medium. Charcoal treatment of dominant follicular fluid did not remove its inhibitory potential. Fractionation of dominant follicular fluid by a desalting column demonstrated that the inhibition was related to a compound(s) > 10 kDa. Finally, the effect of dominant follicular fluid on aromatase appears specific of this enzyme as follicular fluid does not affect androgen output by thecal shells or progesterone output by luteal cells. Further research is required to check whether the activity observed in dominant follicular fluid is related to compounds known to affect aromatase activity (inhibin, mullerian inhibiting substance, heat shock protein 90, superoxyde dismutase) or to another peptide/protein.

Dynamics of ovarian follicular development in cattle during the estrous cycle, early pregnancy and in response to PMSG.

Ovarian follicular dynamics of cattle were examined during the estrous cycle, early pregnancy and in response to PMSG. Number and size of follicles were monitored by ultrasonographic examinations. During the estrous cycle, distinct periods of follicular dominance (measured by the increase in difference in size between the largest and second largest follicle) occurred in both the luteal (Days 6-8) and proestrus (18-22) phases of the estrous cycle (two follicular waves). Associated with the well timed development of the first dominant follicle was a change in distribution of follicle numbers in small (less than 5 mm; increased on Days 2-4), medium (6-8 mm; increased on Days 3-5) and large (greater than or equal to 9 mm; increased on Days 6-9) follicular size classes. Follicular development was greater on the ovary bearing the CL for the period that the CL was present. The dominant follicle formed during the first follicular wave was capable of ovulating (6 of 8 heifers) following an injection of a synthetic analogue of prostaglandin F-2 alpha on Day 9 of the estrous cycle. During early pregnancy (Days 6-34), follicular development (size of largest follicle, number of follicles and total accumulated size of all follicles) on the ovary bearing the CL was suppressed between Days 24 and 34 of pregnancy. This was a local effect in that follicular development was sustained on the contralateral ovary. Therefore, the CL or conceptus may be regulating follicular development in a manner to help prevent luteolysis. Associated with the injection of PMSG was an initial increase in the number of small follicles followed by their recruitment into medium and large size classes leading to ovulation. Number of follicles greater than 5 mm on the Day of estrus was related (r = .97) to the number of subsequent embryos and oocytes collected. Ultrasonography is a valuable technique to monitor ovarian follicular dynamics in cattle, and can thereby be used to infer changes in physiological and endocrine states.

Dynamics of ovarian follicular development in cattle following hysterectomy and during early pregnancy.

Three experiments were conducted to evaluate ovarian follicular dynamics and functional activity during pregnancy in cattle. In 11 pregnant Charolais cows of Experiment I, size of largest follicle, number of follicles and accumulated follicle size were reduced by day 27 of pregnancy on the ovary bearing the corpus luteum (CL) but not on the non-CL bearing ovary. In experiment II, local attenuation of ovarian follicular development on the CL bearing ovary of seven pregnant heifers was evident compared to the contralateral ovary without the CL. However, in four hysterectomized heifers, follicular development was sustained on both the CL- and non-CL bearing ovaries when CL maintenance was achieved without presence of the uterus or conceptus. In Experiment III, steroidogenic characteristics of the largest and second largest follicles at 17 d postestrus were evaluated for seven pregnant and six cyclic cattle. Follicle by physiological status interactions were detected for both aromatase activity of the follicle and follicular fluid concentrations of estradiol and progesterone. In cyclic cows, the largest follicle had appreciably more aromatase activity than did the second largest follicle; whereas, aromatase activity of the largest follicle from pregnant cows was less than that of cyclic cows. However, in pregnant cows the second largest follicle became the estrogen-active follicle, and this follicle occurred with a higher frequency on the ovary contralateral to the CL-bearing ovary. These changes in aromatase activity were reflected by parallel changes in estrogen concentrations of follicular fluid. The higher progesterone concentration in follicular fluid of the largest follicle in pregnant cows provided further confirmation of their atretic status. In conclusion, during early pregnancy the conceptus and/or uterus ipsilateral to the conceptus appear to secrete compounds which alter local follicular steroidogenic activity and attenuate subsequent follicular growth between 17 to 34 d of pregnancy on the CL-bearing ovary. This local mechanism acting within the ovary may contribute to the antiluteolytic effects of early pregnancy in cattle.

Lack of effects of growth hormone administration on ovarian function of lactating goats.

Exogenous growth hormone (GH, 5 mg d-1) was given daily to lactating goats for 4 weeks (Experiment 1) and 100 days (Experiment 2). Treatment effects on milk production and milk composition were assessed. At the end of treatment, goats were slaughtered and one ovary was processed for histological analysis while the largest follicles of the other ovary were dissected, measured and incubated in vitro (Experiment 1). In Experiment 2, following a synchronisation treatment, a superovulatory regime of pregnant mare's serum gonadotrophin (eCG) was given and ovulation rate measured at laparoscopy. In both experiments, GH administration raised milk yield (28.6% and 17% in Experiments 1 and 2 respectively). Circulating IGF1 concentrations were also increased following treatment. In contrast, no treatment effects were detected on the ovaries. In Experiment 1, the total population of antral follicles, their atresia, the number in specific size classes and the size of the largest healthy or atretic follicles were similar in control and GH treated ovaries. In addition, steroidogenesis (oestradiol and testosterone) by large follicles was also unaffected by treatment. In Experiment 2, eCG induced ovulation rate (control 6.9 +/- 7.6, treated 4.2 +/- 2.8) was also similar between groups. It is concluded that GH administration to lactating goats, while increasing milk production has no detrimental or positive consequences on ovarian function.

Seasonal effects on fertility and ovarian follicular growth and maturation in camels (Camelus dromedarius).

Camels are said to be seasonal breeders, but the extent to which season interferes with food supply to affect ovarian function is not fully documented. Hence, the three aims of this study were: (1) to define the breeding season of camels maintained in semi-arid conditions in southern Morocco; (2) to relate the proportion of females with active ovaries (i.e., with follicles > 5 mm), with ovulatory (11-17 mm) or cystic (> 18 mm) follicles to age and body conditions score; (3) to study the consequences of the interactions between age and body conditions score on the proportion of females ovulating and conceiving; and (4) to compare follicular maturation, using in vitro steroidogenesis by intact follicles as a marker during the transition into the breeding season (October) and peak breeding season (March). There was a clear breeding season in the two flocks studied, since over 80-90% of the matings occurred during the period from mid-November to mid-April. Collection of ovaries at slaughter (n = 238) demonstrated a significant seasonal effect on the proportion of females with active ovaries (increasing from 73.5% in October-December to 89% in January-May), but no changes in the proportion of females with ovulatory follicles. Lean females (BCS < 2.5) had a delayed initiation of ovarian function in October-December. In addition, the proportion of females with cystic follicles was also affected by season (peaking during April-May). Neither age nor body condition modulated the frequency of cysts. Finally, the proportion of females conceiving increased steadily as season progressed (peaking at 57% in April-May). Body condition score did not affect this proportion, but young females (< or = 5 years old) had a low ability to conceive. Morphological features of large follicles were unaffected by season. Ovulatory follicles contained around 10(7) granulosa and theca cells. In vitro testosterone output by intact follicles was unrelated to follicle size and season. In vitro oestradiol output increased with increasing follicle size and was larger in follicles obtained during peak breeding season than at its initiation. This may indicate that early breeding season follicles display a low aromatase activity in their granulosa cells. Whether the low oestradiol output of early breeding season follicles is resulting in the low fertility observed at this period remains to be determined.