Follicle population dynamics in sheep with different ovulation rate potentialsDynamique folliculaire terminale chez des ovins de potentiel ovulatoire variéVeränderungen der follikelzahl in schafpopulationen mit unterschiedlich hoher ovulationsrate

To investigate the factors contributing to the different ovulation rates observed in two strains of sheep (Booroola 5.2, Merino, 1.2) and after immunization against androstenedione (Immunized 1.8, Control 1.3), in vivo monitoring of follicular kinetics followed by histological examination of the ovaries was performed during the late luteal and follicular phases. Ewes had the three largest follicles of each ovary ink-labelled at days 13 and 15 and were ovariectomized after the beginning of oestrus.High ovulation rate was not associated with a more numerous antral follicle population in either Booroola ewes or immunized ewes. Furthermore, in Booroola ewes (r = 0.22) and in immunized ewes (r = ?0.02), there was no correlation between the number of antral follicles per ovary and the ovulation rate.The reasons for the high ovulation rate became clear when preovulatory enlargement was followed by ink-labelling. An extended period of time during which recruitment of ovulatory follicles takes place, together with a low incidence of selection through atresia and the ability of fully grown follicles to wait for ovulation are the features involved in the high ovulation rate of the Booroola ewes. A lower incidence of selection together with an unaltered recruitment leads to the increased ovulation rate noticed after immunization.     

Uterine influences on the formation of subnormal corpora lutea in seasonally anestrous ewes

The hypothesis that subnormal luteal function after induced ovulation in anestrous ewes was the result of uterine influences exerted during the periovulatory period was tested. Crossbred ewes (n = 27) in seasonal anestrus were induced to ovulate by administration of 12 doses of 250 ng of LHRH at 2-h intervals, followed immediately by a bolus injection of LHRH (250 micrograms; d 0). Ewes were unilaterally hysterectomized on either d -3 (PRELHRH) or 2 (POSTLHRH). Daily blood samples were collected and assayed for progesterone (P4) and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM). All ewes were slaughtered on d 10, and corpora lutea (CL) were collected, weighed, and assayed for concentration of P4. All ewes that ovulated exclusively in the ovary ipsilateral to the remaining uterine horn had a transient increase in plasma P4 of 2 to 3 d (short luteal phase). In ewes with at least one CL in the isolated ovary, elevated plasma P4 was maintained after hysterectomy but was consistently lower (P less than .05) in POSTLHRH ewes than in PRELHRH ewes. Concentrations of PGFM did not differ between treatments. The CL ipsilateral to the remaining uterine horn weighted less (P less than .01) and contained less P4 (P less than .01) than contralateral CL. These data confirm the hypothesis that premature regression of subnormal CL is uterine-dependent in a local fashion. Presence of the uterus during the follicular and(or) early luteal phase inhibited subsequent luteal function in seasonally anestrous ewes.     

Relationships among the corpus luteum,follicles and conceptus in sheep

This study aimed to investigate the intra- and interovarian relationships among the corpus luteum (CL), the largest follicle (LF) and follicular population in non-pregnant and between the conceptus and ovarian structures in pregnant ewes. In experiment 1, the follicular and luteal structures were examined in 538 reproductive systems of non-pregnant Awassi ewes. The follicular population was categorised into small (SF), medium (MF) and large (LF) groups. Inter-relationships between CL and follicular population and between LF and subordinate follicles were determined. In experiment 2, the location and number of conceptuses were identified and correlated with the ovarian structures in 58 reproductive systems of pregnant ewes. Effects of pregnancy status, stage of pregnancy, pregnancy side and conceptual number on follicular population were determined. The results showed that the right ovary was more active than the left ovary. CL had intraovarian positive effect on the number of medium and large follicles. LF had no local suppressive effect on the subordinate follicles. Side and stage of pregnancy and the conceptual number did not affect the follicular population. Accordingly, it can be concluded that the LF has no local suppressive effect on the subordinate follicles. The CL has intraovarian positive effect on the follicular population. Follicular population does not show remarkable changes during the first term of pregnancy. The present study probably provides information which may help in the understanding of the ovarian dynamics during pregnancy in sheep.     

Leptin infusion during the early luteal phase in ewes does not affect progesterone production

Infusion of leptin during the ovine follicular phase has been shown to increase progesterone secretion during the subsequent luteal phase. In this study, we have assessed the effects of infusing leptin during the early luteal phase. Infusion of leptin (2.5 microg/h) into the ovarian artery of ewes with ovarian autotransplants (n=5) on day 3 of the luteal phase for 12h did not affect progesterone estradiol or LH concentrations compared to control ewes (n=5). These results suggest no direct effect of leptin on ovarian function at this stage of the estrous cycle.     

Effects of Twice-Weekly Follicular Punctures of Ovaries With or Without the Corpus Luteum on Follicular and Luteal Dynamics

We investigated the effects of twice-weekly follicular punctures of ovaries with or without corpus luteum (CL) on follicular and luteal dynamics. A cross-over design was used, with each cow (seven Japanese Black beef cows) being assigned to one of the three groups at 2-month intervals. Follicular punctures were performed twice weekly for three consecutive weeks until day 20 (oestrus = day 0). All visible follicles (diameter >3 mm) in the ovaries bearing CL (ipsilateral group) or those in the contralateral ovaries (contralateral group) were aspirated. As a control, all visible follicles in both ovaries were aspirated (bilateral group). Follicular development, CL formation and progesterone concentrations in each cow were monitored from days 0 to 30. Follicular growth profiles in the punctured ovaries during/after puncture treatment were similar, irrespective of the presence of follicles in the unpunctured ovary and the CL in the punctured or unpunctured ovaries. After puncture, two cows (28.6%) each in the ipsilateral and bilateral groups did not exhibit behavioural oestrus until day 30, whereas all cows in the contralateral group exhibited oestrus. CL growth and increase in progesterone concentrations after the last follicular puncture in the bilateral group were delayed when compared with those in the ipsilateral group. Our results indicate that the presence of follicles in the unpunctured ovary and the CL in the punctured or unpunctured ovaries does not significantly influence follicular growth in punctured ovaries during/after puncture treatment. However, follicular puncture in ovaries bearing CL may disturb or delay oestrus occurrence after treatment.     

The influence of the ovulation rate on ultrasonically determined ovine corpus luteum morphometry and progesterone concentrations in cyclic and early pregnant sheep

The objective of the present study was to describe morphology and function of the Corpora lutea (CL) during the oestrous cycle and early pregnancy in sheep with different ovulation rates. In total 40 Booroola. Mutton Merino crosses [heterozygous carriers (FecBFec+) and non-carriers (Fec+Fec+) of the Booroola-fecundity gene (FecB)] with ovulation rates 1 to 4 were examined. During the oestrous cycle (n = 20) and the first month of pregnancy (n = 20) blood samples were taken daily (radioimmunoassay of progesterone) and an ultrasonic ovary diagnosis was conducted. The ewes were scanned transrectally with a 7.5 MHz linear probe lying in a dorsal position. During every examination the CL could be detected. The number and the diameter of the CL were documented and the total volume of luteal tissue per ewe was calculated. The effect of the ovulation rate on CL-morphology (diameter and total volume of luteal tissue per ewe) and peripheral progesterone concentrations were assessed by one-way ANOVA. On day 6 and 7 post ovulationem in cyclic and early pregnant sheep 42% of the diagnosed CL had a cavity. On day 11 (cyclic sheep) and day 10 post ovulationem (early pregnant sheep) this number decreased to 22% (p < 0.05). Both conditions of the CL (compact or with a central cavity) are similar in function and should be regarded as appearances of the same basic process. From the third day onwards the ovulation rate influenced significantly (p < 0.05) the development of the outside diameters of the CL. However, the ovulation rate had no effect on the total volume of the luteal tissue per sheep and on the progesterone concentrations. Yet, in sheep with the ovulation rate 1 significantly lower progesterone concentrations were determined than in sheep with the ovulation rates 2 to 4. In sheep with the ovulation rates 2 to 4 the peripheral progesterone concentrations did not differ significantly. In cyclic and pregnant sheep there is a positive correlation (r = 0.75, p < 0.05) between the progesterone concentration and the total volume of luteal tissue. Considering the smaller diameters of the preovulatory follicles it seems that the development of the CL continues until a threshold-value of progesterone and/or of the total luteal tissue is exceeded. Ewes with low ovulation rates reach this threshold-value with only a few but large CL. With increasing ovulation rate the CL tend to have smaller diameters.     

Function of ovine corpora lutea after administration of luteinizing hormone-releasing hormone

Ewes were treated with an agonistic analog of luteinizing hormone-releasing hormone (LH-RH) during the luteal phase (d 10) of the estrous cycle. Function of natural and hormonally-induced corpora lutea (CL) was evaluated by measurements of progesterone in sera or luteal tissue. Synthesis and secretion of progesterone by natural CL were not chronically altered by LH-RH. Likewise, there was no in vitro effect of LH-RH on luteal function. When natural CL were surgically removed, newly formed CL functioned at a defective level. Hysterectomy shortly after ovulation did not significantly influence such luteal activity. Induction of ovulation by LH-RH during the follicular phase (d 16) in uterus-intact ewes was followed by normal profiles of luteal secretion of progesterone; serum concentrations of progesterone in animals that were hysterectomized increased in association with development of the CL, but then plateaued at a subnormal level. There were no differences in patterns of secretion of luteinizing hormone in response to LH-RH due to stage of the estrous cycle. Follicles stimulated to ovulate during the luteal phase contained low numbers of steroidogenically-deficient granulosal-lutein cells. These results indicate that: ovine CL are not sensitive to exogenous LH-RH; luteal dysfunction is a consequence of ovulation during the luteal phase, and the etiology of this abnormality appears to be linked with the developmental status of the ovulatory follicle; and CL that are formed from ovulation of a matured follicle begin to develop normally, but then function at a defective rate in the absence of the uterus.     

The localization and expression of epidermal growth factor and epidermal growth factor receptor in bovine ovary during oestrous cycle

Epidermal growth factor (EGF) is one of the important regulatory factors of EGF family. EGF has been indicated to effectively inhibit the apoptosis of follicular cells, to promote the proliferation of granulosa cells and the maturation of oocytes, and to induce ovulation process via binding to epidermal growth factor receptor (EGFR). However, little is known about the distribution and expression of EGF and EGFR in cattle ovary especially during oestrous cycle. In this study, the localization and expression rule of EGF and EGFR in cattle ovaries of follicular phase and luteal phase at different time points in oestrous cycle were investigated by using IHC and real-time qPCR. The results showed that EGF and EGFR in cattle ovary were mainly expressed in granulosa cells, cumulus cells, oocytes, zona pellucida, follicular fluid and theca folliculi externa of follicles. The protein and mRNA expression of EGF/EGFR in follicles changed regularly with the follicular growth wave both in follicular and in luteal phase ovaries. In follicular phase ovaries, the protein expression of EGF and EGFR was higher in antral follicles than that of those in other follicles during follicular growth stage, and the mRNA expression of EGFR was also increased in stage of dominant follicle selection. However, in luteal phase ovaries, the growth of follicles was impeded during corpus luteum development under the action of progesterone secreted by granular lutein cell. The mRNA and protein expressions of EGF and EGFR in ovarian follicles during oestrous cycle indicate that they play a role in promoting follicular development in follicular growth waves and mediating the selection process of dominant follicles.     

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.     

Uterine blood flow during early pregnancy in ewes: interaction between the conceptus and the ovary bearing the corpus luteum

To determine if a transient increase in uterine blood flow (BF) and estradiol-17 beta (E2 beta) secretion occurs during maternal recognition of pregnancy in ewes (as previously observed for sows and cows), 40 nonpregnant (NP) ewes were assigned in equal numbers to surgery on d 9, 11, 13 or 15 postestrus (d 0 = day of estrus). For 20 NP ewes (five/day), each uterine horn (UH) was flushed with saline and uterine flushings (UF) collected. For the remaining 20 ewes, BF was determined for each UH using electromagnetic transducers, and samples of uterine arterial (UA) and uterine venous (UV) blood were obtained from each UH. After an intervening cycle, each ewe was mated, subjected to surgery on the same day postmating as during her previous nonmated cycle, and BF measurements and UA and UV samples were obtained. In addition, each UH of pregnant (P) ewes was flushed and the location of conceptuses was determined. Concentrations of E2 beta and progesterone (P4) in UA and E2 beta in UV and UF were determined by radioimmunoassay. For NP ewes, BF (ml/min) was not different for UH ipsilateral or contralateral to the ovary bearing the corpus luteum (CL), and did not differ across days, averaging 6.5 +/- .4. For P ewes, BF to UH contralateral to the ovary bearing the CL on all days and BF to UH ipsilateral to ovaries bearing CL on d 9 was similar to BF of either UH of NP ewes, averaging 6.8 +/- .6. On d 11, 13 and 15 of pregnancy, BF to UH ipsilateral to the ovary bearing CL was elevated (P less than .01) twofold (13.3 +/- .9).(ABSTRACT TRUNCATED AT 250 WORDS)     

Nutritionally induced body weight loss and ovarian quiescence in Shiba goats

Four female Shiba goats were used to determine the influence of body weight loss by dietary restriction on estrous cyclicity. The dietary restriction was started on the day following ovulation. The goats were fed hay cube and straw at an amount of 30% of energy requirement based on weekly body weight measurement. The ovaries were monitored daily by transrectal ultrasonography and blood samples were collected daily by jugular venipuncture for ovarian steroids analysis. After the start of food restriction, all animals lost body weight and entered ovarian quiescence. Intervals to the onset of ovarian quiescence tended to depend on the body weight of each animal at the start of food restriction. The mean concentration of progesterone during the mid-luteal phase (from 7 to 13 days after ovulation) in the last estrous cycle before ovarian quiescence was significantly lower than that in normal estrous cycle of the control period (19.7 +/- 2.8 vs 12.3 +/- 2.2 ng/ml, P<0.05), whereas there was no significant difference in the length of the luteal phase, determined as the period when corpora lutea existed and concentrations of progesterone were equal to or greater than 1 ng/ml (15.8 +/- 1.5 vs 15.0 +/- 2.8 days, P>0.1). A rise of estradiol concentration and follicular growth in the follicular phase following a decline of progesterone level after luteal regression tended to be suppressed at the onset of ovarian quiescence. It seems that the present results are consistent with previous findings that nutritionally induced body weight loss influences the secretion of ovarian steroids and eventually induces ovarian quiescence.     

Number of mature follicles ovulating after a challenge of human chorionic gonadotropin in different breeds of sheep at different physiological stages

The ovulatory response of ewes from breeds that differ widely in prolificacy (Ile-de-France, ++ Booroola Merino, Romanov, F+ Booroola Merino and F+ Booroola Romanov with adult ovulation rates of about 1.5, 1.2, 3, 3 and 3.5 respectively) to 750 IU of hCG given at different physiological stages (before puberty, during anestrus or during the luteal phase) was compared. In all except one experiment, hCG induced ovulation in 73 to 98% of the lambs, indicating that follicles sensitive to LH were present at all stages studied. Ranking of the breeds according to hCG-induced ovulation rate in prepuberal lambs was similar to that based on adult ovulation rate. Furthermore, hCG induced more ovulations in prepuberal F+ than in ++ lambs (3.7 +/- 1.4 vs 1.7 +/- .8 at 4.5 mo of age) as well as in anestrous ewes (F + at 3.1 +/- 1.8 vs ++ at 1.6 +/- .7). Within ewes, the correlation between hCG-induced ovulation rate and mature ovulation rate was positive in nonprolific breeds but not significant in prolific breeds. We conclude that 1) the number of hCG-induced ovulations can be used to identify sheep that are carriers of the Booroola gene and 2) the mechanisms responsible for a number of large ovulatory follicles typical of a breed are present at stages (prepuberal, anestrus, luteal phase) other than the follicular phase.     

Expression and Localization of Gap Junctional Connexins 26 and 43 in Bovine Periovulatory Follicles and in Corpus Luteum During Different Functional Stages of Oestrous Cycle and Pregnancy

The aim of this study was to characterize the regulation of connexins (Cx26 and Cx43) in the bovine ovary (experiment 1–3). Experiment 1: ovaries containing preovulatory follicles or corpora lutea (CL) were collected at 0, 4, 10, 20, 25 (follicles) and 60 h (CL) relative to injection of GnRH. Experiment 2: CL were assigned to the following stages: days 1–2, 3–4, 5–7, 8–12, 13–16, >18 (after regression) of oestrous cycle and of early and late pregnancy (<4 and >4 months). Experiment 3: induced luteolysis, cows on days 8–12 were injected with PGF2α analogue (Cloprostenol), and CL were collected by transvaginal ovariectomy before and 0.5, 2, 4, 12, 24, 48 and 64 h after PGF2α injection. Real‐time RT‐PCR was applied to investigate mRNA expression and immunofluorescence was utilized for protein localization. Cx26 mRNA increased rapidly 4 h after GnRH injection (during LH surge) and decreased afterwards during the whole experimental period. Cx43 mRNA expression decreased continuously after GnRH application. Cx26 mRNA in CL increased significantly in the second part of oestrous cycle and after regression. In contrast, the highest mRNA expression for Cx43 in CL was detected during the early luteal phase. After induced luteolysis the mRNA expression of Cx26 increased significantly at 24 h. As shown by immunofluorescence, Cx26 was predominantly localized in the connective tissue and blood vessels of bovine CL, whereas Cx43 was present in the luteal cells and blood vessels. This resulted in a strong increase of Cx26 expression during the late luteal phase and after luteal regression. Subsequently, Cx43 expression was distinctly decreased after luteal regression. These data suggest that Cx26 and Cx43 are involved in the local cellular mechanisms participating in tissue remodelling during the critical time around periovulation as well as during CL formation (angiogenesis), function and regression in the bovine ovary.     

Neural regulation of the bovine corpus luteum

The ovarian noradrenergic stimulation or noradrenaline (NA) administration directly to the ovary in cow increases ovarian oxytocin (OT) release and post-translational processing of OT synthesis within a few minutes has been established in both in vivo and in vitro studies. Furthermore, NA affects progesterone secretion and its synthesis by an increase of cytochrome P450scc and 3beta-hydroxysteroid dehydrogenase activity. This effect is mediated via luteal cell beta(1)- and beta(2)-receptors. Their total amount correlates with peripheral progesterone concentrations during the luteal phase and this reflects the ability of the ovary to react to beta-stimulation. On the other hand, ovarian denervation causes a decrease of steroidogenic activity in the CL, an increase of beta-receptors on luteal cells, a delay in follicular development and the disruption of cyclicity. Moreover, decrease of progesterone secretion by 20-30% was seen after brief pharmacological blockade of ovarian beta-receptors in the mid-cycle of cattle. We assume that tonic beta-stimulation of the CL ensures the basal secretion of progesterone, whereas acute noradrenergic activation supports the CL during stressful situations which could impair its function. Conversely, long-lasting increase in blood catecholamine concentrations markedly decreases the number of beta-receptors in CL, presumably due to their down-regulation. Concentrations of dopamine (DA) within the CL are highly correlated with those of NA during the estrous cycle, and are higher in the newly-formed than in the developed corpus luteum, the regressed corpus luteum or the corpus luteum of pregnant females. Bovine CL can synthesise de novo NA from DA as a precursor. Concluding, presented data indicate that noradrenergic stimulation can be an important part of mechanism supporting secretory function of CL.     

Ovarian activity,transuterine embryo migration and prenatal losses in Ethiopian highland ewes

A study was conducted on 1442 Ethiopian highland ewes to determine the seasonality of ovarian activity, intrauterine embryo migration and prenatal reproductive wastage. Assessment of ovarian follicular activity revealed that a higher (p < 0.01) proportion of ewes ovulated in the dry season than in the heavy and light rainy seasons. However, there was a tendency (p = 0.057) of decline in the mean number of ovulations per ewes during the light rains. The mean diameter of the largest follicle on the ipsilateral ovary was higher (p < 0.01) in both ewes with single and those with twin corpora lutea (CL) than on the contralateral ovary; and, compared to ewes with single CL, it was higher (p < 0.05) in those with twin CL. The right ovary was more active (p < 0.001) only in single-ovulating ewes. Similarly, a higher (p < 0.001) proportion of ewes were pregnant in the right horn. Embryos migrated to the opposite horn in single-, twin- and triple-ovulating ewes. There was a higher (p < 0.001) tendency for the left-to-right migration than the opposite. There was significant (p < 0.01) association between embryo loss and site and number of ovulations. Embryo loss was higher (p < 0.01) in ewes with twin ovulations on the right ovary. It is very likely that these results indicate a better chance of embryo survival in the right uterine horn.     

Effect of ovarian follicles on luteal regression in heifers

Our objectives were to determine whether or not ovarian follicles contribute to spontaneous luteal regression in heifers and, if so, when during diestrus do follicles exert their effect. Thirty-one Holstein heifers having displayed at least one estrous cycle (19 to 21 d) were assigned, as available, to randomized blocks for a factorial experiment. Reproductive organs were exposed through a midventral incision on d 9, 12 or 15 postestrus (estrus = d 0). Visible follicles were electrocauterized and both ovaries were x-irradiated (1,500 rads) in treated heifers, whereas ovaries of controls were exteriorized but follicles were not destroyed and ovaries were not x-irradiated. In two additional heifers, the ovary containing the corpus luteum was exteriorized and x-irradiated on d 15 postestrus, but follicles were not electrocauterized. Jugular blood was collected before and every 8 h after surgery until d 24 postestrus. All heifers were ovariectomized on d 24 postestrus to inventory follicles and to weigh corpora lutea. No follicles (greater than or equal to 1 mm diameter) were observed in ovaries from treated animals and concentrations of estradiol-17 beta did not change over time, whereas different numbers of follicles were observed in ovaries from controls and concentrations of estradiol-17 beta increased (P less than .05) during proestrus. Hence, treatment destroyed follicles and prevented follicular development. On d 24 postestrus, corpora lutea from treated heifers (5.5 +/- .5 g) were heavier (P less than .001) than corpora lutea from controls (1.1 +/- .1 g), independent of day when follicles were destroyed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrinology of the postpartum period in the Pelibuey ewe

The postpartum (PP) period in the Pelibuey ewe was studied. Laparotomies were performed on 14 ewes in the first year at d 10, 20 and 30 PP, and at d 10 and 20 PP in the second year on 17 ewes. Progesterone concentrations were determined in serum taken daily, from 4 to 7 d after parturition until estrus. Temporal fluctuation of luteinizing hormone (LH) was determined in samples taken at 30-min intervals for 4 h weekly. The mean interval from lambing to first ovulation was longer (P less than .001) in 1980 (59 +/- 4.9 d) than 1979 (26 +/- 3.1 d), the mean interval from lambing to first estrus was also longer (P less than .001) in 1980 (91 +/- 5.6 d) than 1979 (51 +/- 5.5 d). Follicles were present on the ovaries of the majority of the ewes at d 10. The mean diameter of the largest follicles on each ovary was reduced (P less than .025) in ewes in 1980 (6 mm) compared with 1979 (7.7 mm). Corpora lutea (CL) occurred in 67 and 75% of the ewes by d 20 and 30, respectively in 1979; no CL were found by d 20 in 1980. Progesterone profiles suggested that the PP period was composed of a period of anestrus, and a period of cyclic ovarian activity with one, two or three ovulations without behavioral estrus. In some ewes, the first cycle was of shorter duration, and its CL secreted less progesterone (P less than .05) relative to CL of silent and regular estrous cycles. Luteinizing hormone peaks were recorded as early as 6 d PP. When progesterone concentrations were elevated to luteal phase levels, the frequency, but not magnitude, of LH peaks per 4-h bleeding period was reduced (P less than .05) relative to anestrus. It is concluded that there are periods of anestrus and of silent cycles, which precede the first postpartum estrus in Pelibuey ewes.     

An Ultrasonographic Method to Study Reproductive Seasonality in Ewes Isolated from Rams

In studies concerning the seasonality in sheep, the effect of the teaser-ram, which can by itself induce oestrus as well as the development of ovary function bodies, has not been considered. In this study, a method is developed to determine ovarian activity during the year while excluding a possible influence of the ram. The study was carried out on 10 German Blackhead Mutton ewes (GBM) and 10 German Mutton Merino ewes (GMM) and lasted for 14 months. The ewes were kept without contact with any ram, and once a week a transrectal ultrasonography was conducted to determine ovary function bodies (corpora lutea, follicles) and a blood sample was taken to analyse progesterone (P4) concentration. In both breeds, the number of ovulating ewes, the ovulation rate (OR), the size of the corpora lutea (CL) and P4-concentrations showed significant seasonal fluctuations. During the main breeding period (September-February), the OR was higher (2.0 +/- 0.4) than during the rest of the year (1.6 +/- 0.5). Outside the main breeding season (March-August), approximately 40% GBM ewes and only approximately 15% GMM ewes produced CL. The cycle and the related seasonal changes in the P4-concentration coincide with different ultrasonically diagnosed CL (developing or regressing, insufficient, no CL). Between the volume of fully developed CL and P4-concentration, correlations of 0.57 (GMM) and 0.45 (GBM), respectively, were found. On average, P4-concentration in September to February was by approximately 1.60-1.66 nmol/l in the GMM and by approximately 1.80-1.86 nmol/l in the GBM higher than in spring and summer. Considering the OR, the P4-values corresponded with the CL volumes, i.e. in the months from August to February the CL values were significantly larger than in the months March to August. The ultrasonic ovarian diagnosis is a useful method to determine the ram-uninfluenced seasonality of reproduction in sheep.