Ovarian Structure and Oogenesis of Catfish Pimelodella vittata (Lütken, 1874) (Siluriformes,Heptapteridae)

The morphology of the ovaries and oogenesis of Pimelodella vittata were studied using anatomical and histological techniques to provide information of its reproductive biology. Eighty adult females were captured trimonthly during the period November 2005 to October 2006. The ovaries are paired, saculiform organs, which are coated with tunica albuginea and contain ovigerous lamellae, where the oocytes develop before being released into the ovarian lumen and following the ovarian duct until reaching the genital papilla. Oogenesis was divided into stages based on the alterations to the nucleus, ooplasm and surrounding follicular layers. Oogonia form groups from the germinal epithelium have asynchronous development and differentiate into initial perinucleolar oocytes. The formation of the zona pellucida is initiated in the advanced perinucleolar oocytes reaching a thickness of 1.46 ± 0.58 μm in the vitellogenic oocytes. The follicular cells are squamous in perinucleolar oocytes, become cubical in the pre‐vitellogenic oocytes and prismatic in the vitellogenic oocytes with a height of 11.20 ± 4.74 μm. The histochemical reactions indicate that zona pellucida, cortical alveoli and yolk globules contain neutral glycoproteins and the follicular cells contain neutral glycoproteins in association with carboxylated and sulphated glycoconjugates. Statistical analyses showed significant differences in the diameter of the oocytes and follicular cells height as oocytes matured. This study represents the first data about the ovarian structure and oogenesis of this species.     

The reproductive biology of the moony,Monodactylus falciformis,in Algoa Bay

Gonadosomatic indices, macroscopic and microscopic examinations of gonads were used to establish the breeding cycle of Monodactylus falciformis. Spawning took place between October and February and evidence for serial spawning is presented.     

Physiological changes during the ovarian cycle of the female rock lizard,Agama atra (Sauria: agamidae)

Seasonal morphometric and physiological changes associated with vltellogenesis in the female agamid lizard, Agama atra are described. Vitellogenic activity during August - September marked the onset of the breeding season. It is suggested that at least two clutches were ovulated during the breeding season. Large abdominal fatbodles deposited prior to the winter months were possibly utilized to meet metabolic demands during winter and the onset of vitellogenesis during early spring (August - September). Follicular growth and fatbody deposition coincided with low plasma cholesterol levels. The liver index and total plasma proteins did not show a clear seasonal pattern. Of the seven plasma protein fractions, Fraction 2 (‘human beta-globulin’ mobility) increased during vltellogenesis while the foremost migrating proteins (‘human albumin’ mobility) showed a compensatory decrease. Total plasma calcium levels increased during vitellogenesis. The oviducts remained hypertrophied throughout the breeding season, while progesterone levels increased following each ovulation cycle in the presence of corpora lutea and remained elevated until oviposition. The onset of the second vitellogenic cycle (December) coincided with high progesterone levels.     

Post-mortem recovery,in vitro maturation and fertilization of fallow deer (Dama dama,Linnaeus 1758) oocytes collected during reproductive and no reproductive season

Habitat degradation leads to small and fragmented populations, lower genetic variability and fertility overtime. Assisted reproductive techniques represent important tools to cope with the dramatic loss of biodiversity. Fallow deer (Dama dama), beyond its high commercial value and wide distribution, may represent the most suitable model to study endangered cervids. In this study, oocytes were recovered post-mortem from fallow deer during the breeding and no breeding seasons and were in vitro matured (IVM). The ability of cryopreserved thawed sperm samples recovered by electroejaculation from four adult males was tested by in vitro fertilization of IVM oocytes. The number of oocytes collected per ovary did significantly vary across seasons from 6.2 ± 0.92 during breeding season to 10.4 ± 1.26 during no breeding season (p = .006). Oocytes collected during the breeding season showed higher in vitro fertilization rate compared to the no breeding season (p = .045). However, no embryos reached the blastocyst stage. Semen samples obtained by electroejaculation were successfully cryopreserved, although the cryopreservation process negatively affected most kinetic parameters, mainly at 2 hr post-thawing. Moreover, the percentage of rapid spermatozoa significantly decreased between fresh samples and at 2 hr post-thawing, whereas the percentage of slow spermatozoa increased across the same period (p < .05). Our study provides the logistic steps for the application of assisted reproductive techniques in fallow deer and might be of great interest for genetic resource bank planning.     

Cumulus–Oocyte Communications in the Horse: Role of the Breeding Season and of the Maturation Medium

Horse is a seasonal breeder and information on oocyte quality outside the breeding season is very limited. Ovaries obtained at the slaughterhouse are a convenient but often limited source of oocytes in this species. As the low quantity of ovaries leads to an intensive use of all available material, it would be useful to know whether ovaries collected during the non‐breeding season are suitable for in vitro maturation (IVM). In an attempt to characterize the effect of season on oocyte quality, we investigated the permeability of the gap junctions (GJ) present between cumulus cells and oocytes because of their important role in oocyte growth and maturation. We also compared the effect of supplementing the maturation medium with bovine serum albumin (BSA) or oestrus mare serum (EMS). A total of 645 oocytes isolated from 158 and 154 ovaries collected during the breeding and the non‐breeding season, respectively, were used in this study. Oocytes were matured for 30 h in TCM 199 supplemented either with 10% EMS or with 4 mg/ml BSA. The presence of permeable GJs between cumulus cells and oocytes was investigated with the injection of a 3% solution of the fluorescent dye Lucifer yellow into the ooplasm. No differences in efficiency of oocyte retrieval or oocyte meiotic competence were detected between oocytes collected during the breeding and non‐breeding season. The vast majority (90%) of the oocytes collected during the breeding season had fully functional communications with their surrounding cumulus cells but such communications were completely interrupted in 55.3% of the oocytes collected during the non‐breeding season. During the non‐breeding season, the proportion of oocytes whose communications with cumulus cells were classified as closed or intermediate at the end of maturation was lower in the group matured with BSA than with EMS (71.4 vs 97.7, p < 0.05). The same trend, although not statistically significant, was observed during the breeding season also. The presence of BSA caused an incomplete cumulus expansion during both seasons. Our data indicate that oocytes collected during the non‐breeding season do not show any meiotic deficiency but lack active communication with the surrounding cumulus cells at the time of their isolation from the ovary. No data are available at present for determining the consequences on the developmental competence even if data from other species suggest that this is likely.     

The Female Reproductive Cycle of the Neotropical Snake Atractus pantostictus (Fernandes and Puorto, 1993) from South‐eastern Brazil

Data on reproductive activity of fossorial species are limited because the specimens are difficult to be observed and captured. Here in, we present the reproductive cycle of female Atractus pantostictus, a fossorial neotropical species, and the sexual maturity of males and females in south‐eastern Brazil. The female reproductive cycle of A. pantostictus is seasonal, with vitellogenic follicles being found from September to April and eggs in November, February, March and April with the number varying between two and four. Spermatozoa were found in the lumen of the glandular and non‐glandular uterus in females collected during the rainy season. Sperm storage tubules were found in the posterior infundibulum of the females, where the storage of sperm occurs for a short time. The storage may occur because mating and ovulation are dissociated.     

Effect of Reproductive Seasonality on Gamete Quality in the North American Bison (Bison bison bison)

The objective was to investigate the effects of reproductive seasonality on gamete quality in plains bison (Bison bison bison). Epididymal sperm (n = 61 per season), collected during the breeding season (July–September), had significantly higher post‐thaw total motility (36.76 ± 14.18 vs 31.24 ± 12.74%), and lower linearity (0.36 ± 0.06 vs 0.39 ± 0.04) and wobbliness (0.49 ± 0.04 vs 0.51 ± 0.03; mean ± SD) compared to non‐breeding season (January–March) samples. Representative samples (n = 4) from each season were used in heterologous IVF trials using cattle oocytes. Cleavage, morulae and blastocyst percentage were higher for breeding vs non‐breeding season sperm samples (81.88 ± 6.8 vs 49.94 ± 6.77; 41.89 ± 13.40 vs 27.08 ± 23.21; and 30.49 ± 17.87 vs 13.72 ± 18.98%, respectively). Plains bison ovaries collected during the breeding (n = 97 pairs) and non‐breeding (n = 100 pairs) seasons were classified as luteal or follicular. Oocytes recovered from these ovaries were classified into five grades based on morphology. There was no significant difference in the number of luteal ovaries or grades of oocytes recovered. Oocytes were matured, fertilized (with frozen sperm from three bison bulls) and cultured in vitro. Cleavage percentage was higher for oocytes collected during breeding vs non‐breeding season (83.72 ± 6.42 vs 73.98 ± 6.43), with no significant difference in subsequent development to blastocysts. In summary, epididymal sperm from non‐breeding season had decreased total motility and resulted in reduced embryo production in vitro. Oocytes collected during non‐breeding season had reduced ability to be matured, fertilized and/or undergo cleavage in vitro. Data suggested that season influenced gamete quality in plains bison.     

Effects of the estrous cycle on the efficacy of oocyte collection and in vitro embryo production in Duroc‐breed

Collection efficacy and in vitro embryo developmental ability of oocytes obtained from Duroc‐breed ovary donors at different stages of the estrous cycle (days 6, 12 and 16 after estrus) were performed. The numbers of collected oocytes did not differ significantly among the different estrous cycle groups (total 72–90 oocytes per gilt). However, the blastocyst rates of oocytes collected on days 12 and 16 (9.2% and 19.4%, respectively) were significantly higher than those on day 6 (1.1%). More oocytes were obtained on day 16 from small follicles (<2 mm in diameter; 85.3 oocytes per gilt) than from medium‐sized (≥2–<6 mm) and large (≥6 mm) follicles (17.5 and 12.8 oocytes, respectively). The blastocyst rates in both the medium‐sized and large follicle groups (20.0% and 19.2%, respectively) were significantly higher than that in the small follicle group (6.3%). The blastocyst cell numbers in both the medium‐sized and large follicle groups (39.4 and 43.3 cells, respectively) were significantly higher than that in the small follicle group (30.6 cells). The results suggest that oocyte collection from cycling Duroc pigs can be carried out efficiently from the late luteal to follicular stage. Those oocytes collected from medium‐sized and large follicles show better embryo development.     

Effects of the Reproductive Status on Morphological Oocyte Quality and Developmental Competence of Oocytes after In Vitro Fertilization and Somatic Cell Nuclear Transfer in Cat

This study was conducted to examine the effects of the reproductive cycle of donor cat on the quality of oocytes at recovery and developmental competence of oocytes after in vitro fertilization (IVF) and somatic cell nuclear transfer (NT). Based on the presence or absence of follicles and corpora lutea, the ovarian pairs collected were classified into inactive, follicular or luteal stages. After collection of oocytes, the oocytes were classified into four grades according to the morphological condition of oocyte cytoplasm and cumulus cells. A total of 16 558 oocytes were obtained from 198 ovarian pairs. The total mean numbers of oocytes and the mean numbers of oocytes with high quality (grade I) were significantly higher in ovarian pairs at the inactive stage (111.1 and 19.0 oocytes, respectively) than in ovarian pairs at the follicular stage (67.1 and 11.4 oocytes, respectively). A significant difference in the proportions of oocytes with grade I out of the total examined oocytes was observed between the follicular and luteal stages of ovaries (14.9% vs 20.2%, p < 0.05). The proportions of IVF embryos cleaved and developed to blastocysts significantly decreased with decreased quality of oocytes at recovery, irrespective of the reproductive status of ovaries. Moreover, there were no significant differences in the proportions of cleavage and development to the blastocyst stage of IVF and NT embryos among three oestrous stages of ovaries. These results indicate that the reproductive cycle stage of donor cat ovaries has no apparent effects on the in vitro development of oocytes after IVF and NT, but the quality of oocytes at recovery influences the development of IVF embryos.     

In Vitro Maturation of Oocytes from Norwegian Semi-domestic Reindeer (Rangifer tarandus)

In vitro maturation of oocytes has been described for several species, but to our knowledge this is the first attempt to mature oocytes from reindeer in vitro. Reindeer are seasonal breeders with their main period of breeding activity starting in the beginning of October. Little knowledge exists about in vivo oocyte maturation, fertilization and development of the early embryonic stages after fertilization. The aim of the present study was to examine whether reindeer oocytes collected out of breeding season could be matured in vitro in conventional medias used for bovine oocytes.     

The post-ovulatory rise in progesterone is lower and the persistence of oestrous behaviour longer during the first compared with the second cycle of the breeding season in mares

Mares are seasonally polyoestrous breeders. Therefore, the first ovulation of the season, following winter anoestrus, is the only cycle in which mares ovulate without the presence of an old CL from the previous cycle. The objective of this study was to compare the length of oestrous behaviour, and plasma progesterone concentrations during the early post-ovulatory period between mares after the first and second ovulation of the breeding season. Overall, 38 mares and 167 oestrous periods were used in the study. From those, 11 mares were used during the first and subsequent oestrous period to measure and compare the post-ovulatory rise in progesterone concentration, whereas all the mares were used to compare the length of the post-ovulatory oestrous behaviour between the first and subsequent cycles of the breeding season. The persistence of the post-ovulatory oestrus was longer (p < .001) following the first ovulation of the year (median of 52 h) compared with the subsequent ovulations (median of 36 h for second and later ovulations groups; n = 38 mares). The progesterone concentration at any of the four 8 h-intervals analysed (28, 36, 76 and 84 h post-ovulation) was lower (p < .01) following the first versus the second ovulation of the year. By 36 h post-ovulation the progesterone concentration of mares at the second ovulation of the year had passed the threshold of 2 ng/ml (2.1 ± 0.33 ng/ml), whereas in the first cycle it was 1.2 ± 0.13 ng/ml. In conclusion, mares had lower progesterone concentrations in their peripheral circulation and longer persistence of oestrous behaviour following the first ovulation of the year compared with the second and subsequent ovulatory periods of the breeding season.     

Gonadal Development of the Piau Leporinus copelandii (Characiformes,Anostomidae) in a Tropical River in South‐eastern Brazil

Histological analysis of the gonadal development of Leporinus copelandii Steindachner, 1875, a rheophilic Characiformes species in the Paraiba do Sul River, South‐eastern Brazil, was described. We expect that this species adapt gonadal development to succeed in this river basin that has its longitudinal profile blocked by several impoundments. Fishes were examined by routine macroscopic and histological techniques. Stages of oocyte and spermatocyte development were described, and gonadal maturation was proposed. Mean oocyte diameter obtained from histological observations increased from the pre‐spawning (4.2–175.5 μm) to spawning (148.5–262.0 μm) phases, followed by a sharp decrease in the post‐spawning (27.0–56.7 μm) phase. Based on occurrence of different oocytes phases and oocyte size distribution, this species has group‐synchronic development of oocytes. Further studies are necessary to clarify the spawning grounds for L. copelandii in the Paraíba do Sul River basin, especially considering that several impoundments obliterate the natural river course and this could limit spawning grounds.     

An ultrastructural characterization of the ooplasm in ovarian follicles of the immature ostrich (Struthio camelus)

Primordial, pre-vitellogenic and vitellogenic follicles were present in the ovary of the immature ostrich. The oocytes of these follicles were composed of a nucleus surrounded by ooplasm. Central, intermediate and cortical regions formed the ooplasm. The organelles present in these ooplasmic regions varied depending on the stage of follicular development. In primordial and small pre-vitellogenic (100-150 microm in diameter) follicles the central region of the ooplasm was dominated by an accumulation of organelles, which formed Balbiani's vitelline body. In contrast, the central region in vitellogenic follicles was filled with numerous large yolk spheres, many of which contained lining bodies. Numerous lipid droplets interspersed with mitochondria and small yolk spheres formed the intermediate ooplasmic region in primordial and small pre-vitellogenic follicles. In large pre-vitellogenic (150-400 microm in diameter) and vitellogenic follicles the intermediate region contained a greater density of mitochondria and small yolk spheres. Small yolk spheres were observed in the cortical region of pre-vitellogenic follicles. An interesting feature of the cortical region in vitellogenic follicles was the frequent occurrence of Golgi complexes. The results of the study indicate that although the ovarian follicles in the immature ostrich are not ovulated, the components and composition of the ooplasm are similar to those observed in the mature follicles of other avian species.     

Effects of Hormonal Supplementation on Nuclear Maturation and Cortical Granules Distribution of Canine Oocytes During Various Reproductive Stages

The aim of this study was to evaluate the effects of hCG, progesterone and oestradiol supplementation on nuclear and cytoplasmic maturation of canine oocytes cultured for 24, 48, 72 and 96 h. Oocytes obtained from 18 healthy bitches were divided into three groups according to their reproductive status (follicular, luteal and anoestrus stages) and cultured in TCM 199 + 25 UI/ml of hCG + 1 μg/ml of progesterone + 1 μg/ml of 17‐β oestradiol or without hormonal supplementation (control) for different periods. Then, they were stained with FITC‐LCA‐Hoescht for chromatin configuration and cortical granules distribution and evaluated under an epifluorescence microscope. Culture time and the influence of different stages of the oestrous cycle were also evaluated. The present study demonstrated that there was no significant difference among the reproductive stages. With regards to culture medium, only oocytes from the supplemented medium were able to complete meiosis; however, significant difference was only noticed in the percentage of MI stage oocytes (p < 0.05) in the follicular and luteal group at 72 h of culture. Most oocytes in germinal vesicle, germinal vesicle breakdown and metaphase I stage had cortical granules distributed throughout the cytoplasm (immature pattern), irrespective of the culture period (p < 0.05). Cortical granules distributed immediately beneath the plasma membrane (mature) was only observed in metaphase II stage oocytes, but not all of them presented matured cytoplasm. Our results reveal that cortical granules distribution in canine oocytes matured in vitro did not progressed in correspondence with nuclear stage changes and are in accordance with those from other species.     

Oogenesis is accompanied by cyclic morphological changes in hepatocytes of Neotropical freshwater fish Piabina argentea

We determined for the first time the reproductive biology of Piabina argentea through macroscopic and microscopic analysis of ovaries and evaluated the morphological changes in hepatocytes. Two hundred and 46 specimens were collected, 204 females and 42 males, between March 2014 and February 2015. Biometrics data were obtained. From females, gonad and liver samples were conducted to histological, histochemical and immunohistochemical techniques. Mature ovaries were used to determine absolute and relative fecundity. Total length and body weight values indicated that females were larger than males. The estimated weight–length ratio showed negative allometric growth. The absolute fecundity average was 171.83 ± 59.89 oocytes per ovary. In addition, females spawning capable and regressing stages were found throughout the sampling period and the presence of all oocyte types in regressing stage ovaries indicated asynchronous oocyte development and multiple spawning. From regenerating to spawning capable stage the oocytes accumulated yolk in cytoplasm became bigger. While in the liver hepatocytes with a larger cell area during regenerating stage and proliferative activity in the spawning capable stage were observed. Thus, our results indicate that P. argentea had an opportunistic reproductive strategy and cyclic morphological changes of hepatocytes occurred during the oogenesis.     

Quantifying the occurrence of early embryonic mortality on three equine breeding farms

This prospective field study was designed to describe the incidence of early embryonic mortality (EEM) and factors associated with the cause of EEM on three equine breeding farms in Ontario during the 1989 breeding season. Early embryonic mortality was defined as the loss of a single embryo during the first 40 days of pregnancy (day 0 = day of ovulation or last breeding). Pregnancy diagnoses and subsequent embryonic losses were observed by serial trans-rectal ultrasonography between days 12-20 (PD1) and 21-30 (PD2), and by trans-rectal ultrasonography or palpation per rectum between days 31-40 (PD3). Information on pregnancy status of a mare (or cycle) at 40 days after the last breeding was recorded when available. Nonpregnancy rates were calculated on a per cycle basis, to account for mares with no ultrasonic evidence of an embryo at the initial pregnancy examination. Embryonic mortality rates per cycle were calculated cumulatively (EMR₍₄₀₎) for the entire 40 day embryonic period and during the specific time periods when a pregnancy diagnosis took place (EMR_(PD1), EMR_(PD2), EMR_(PD3)). Embryonic mortality rates were also calculated on a per mare basis for mares experiencing EEM on either their first (EMR_(f)) or any (EMR_(a)) breeding cycle. Per cycle mare withdrawal rates were calculated cumulatively for the entire 40 day embryonic period (MWR₍₄₀₎), and at each specific pregnancy diagnosis time period (MWR_(PD1), MWR_(PD2), MWR_(PD3)) to account for those breeding cycles in which mares were not able to be observed for the entire forty days of the embryonic period. Records from a total of 699 mares involving 1014 breeding cycles were examined and analyzed. Per cycle risk rates for nonpregnancy (NP) were 36.4%, 45.0%, and 22.1%, for farms 1,2 and 3, respectively. Per cycle EMR₍₄₀₎ ranged from 8-17%. Per cycle MWR₍₄₀₎ ranged from 56.5-98.9%, indicative of a high rate of mare withdrawal from the study for the duration of the “embryonic” period. Significant differences (p < 0.05) in EMR_(f) and EMR_(a) per mare existed between two farms, indicative of a farm effect on EMR. Multivariable forward stepwise logistic regression analyses revealed that mares bred on foal heat were 1.9 times more likely than mares not bred on foal-heat to experience EEM (p = 0.008).     

利用JIVET技术快速繁育萨福克羊的研究

JIVET技术是一项利用生殖激素刺激幼畜卵巢,从而使其快速、高效生产卵母细胞的技术。对4只1月龄萨福克幼羔注射FSH和PMSG激素,48 h后采用手术法抽取幼羔卵母细胞,并在体外成熟;将成熟的卵母细胞与精子进行体外受精,将正常分裂的2~8细胞胚胎移植到6只同期发情的受体小尾寒羊子宫内。结果显示,采用激素法处理萨福克幼羔后共采集到可用卵母细胞109枚,体外成熟培养后得到成熟卵母细胞79枚,成熟率为72.48%;体外受精后得到正常卵裂胚胎34枚,卵裂率为43.04%;胚胎移植后有3只受体母羊怀孕,受胎率为50%,并分娩得到3只萨福克幼羔。综上提示,利用JIVET技术可以缩短萨福克羊的繁育周期,从而加快其繁育速度。     

Effects of meiotic inhibitors and gonadotrophins on porcine oocytes in vitro maturation,fertilization and development

This study evaluated the effect of three reversible meiotic inhibitors (MINs) and their interaction with gonadotrophins (Gns) on the meiotic maturation and developmental competence of porcine oocytes. In experiment 1, the oocytes were matured for 22 hr in the presence or absence of dbcAMP (1 mM), cycloheximide (7 μM) or cilostamide (20 μM) with or without Gns, and for an additional 22 hr in the absence of MINs and Gns. At 22 hr of maturation, regardless of the presence of Gns, a higher proportion (p < .001) of oocytes cultured in the presence of MINs were effectively arrested at the germinal vesicle stage compared with the oocytes cultured without MINs. At 44 hr of maturation, the proportion of oocytes that reached MII was higher (p < .05) in groups with Gns compared with groups without Gns. In experiment 2, oocytes that were matured as in experiment 1 were inseminated and cultured for 7 days to evaluate fertilization parameters and blastocyst formation. Only oocytes from the dbcAMP + Gns group had higher (p < .05) efficiency of fertilization compared with the other treatment groups. The presence of dbcAMP during maturation also increased (p < .05) blastocyst formation and efficiency of blastocyst formation in both the presence and absence of Gns. These results indicate that the interaction of Gns with the tested MINs improved meiotic progression. In addition, regardless of supplementation with Gns, the presence of dbcAMP during the first maturation period increased and even doubled the capacity of oocytes to develop to the blastocyst stage.     

Morphological Quality of Oocytes and Blood Plasma Metabolites in Repeat Breeding and Early Lactation Dairy Cows

The objectives of the study were to evaluate the morphological quality of oocytes in repeat breeder and early lactation cows and to determine the possible associations between the quality of oocytes and a range of blood metabolites. Oocyte quality and a range of metabolites were compared between 29 repeat breeder and 13 early lactation cows. The yield of oocytes from the repeat breeders was lower than that from the early lactation cows (4.4 ± 0.2 vs 5.4 ± 0.6, p < 0.05). Percentages of abnormal oocytes for the repeat breeders and the early lactation cows were 52.5% and 37.9%, respectively (p < 0.001). An excess of abnormal oocytes to normal was found in 55.2% of the studied repeat breeders (65.8% vs 34.2%, p < 0.05). Total protein, glucose and aspartate aminotransferase did not differ (p > 0.05) between the repeat breeders with an excess of abnormal oocytes (81 ± 1.0 g/l, 3.5 ± 1.0 mmol/l and 68.5 ± 3.7 U/l), those with the prevalence of normal oocytes (84 ± 1.0 g/l, 3.6 ± 0.1 mmol/l and 73.2 ± 3.5 U/l) and the early lactation cows (83 ± 2.0 g/l, 3.7 ± 0.1 mmol/l and 74.5 ± 3.6 U/I). The repeat breeders with an excess of abnormal oocytes had higher (p < 0.05) urea (5.2 ± 0.2 mmol/l) level than in those with the prevalence of normal oocytes (4.8 ± 0.2 mmol/l) and the early lactation cows (4.7 ± 0.2 mmol/l). A trend for higher total cholesterol and lactate dehydrogenase activity was found in the repeat breeders with an excess of abnormal oocytes. In conclusion, it is suggested that possible causes of repeat breeding in dairy cows may include impaired oocytes. An excess of abnormal oocytes in the repeat breeder cows was associated with elevated blood plasma levels of urea.     

Follicular development after ovum pick-up and fertilizability of retrieved oocytes in postpartum dairy cattle

This study aimed to evaluate gonadotropin secretion and the developmental competence of follicular oocytes in dairy cattle during the early postpartum (PP) period. The number of follicles developed after transvaginal ultrasound-guided ovum pick-up (OPU) and fertilizability of retrieved oocytes were compared between cows in which the first dominant follicle (DF) ovulated (ovulated group, n=4) and did not ovulate (non-ovulated group, n=3), and between early PP (early PP group, n=2) and after the resumption of the estrous cycle (cyclic group, n=2). Follicular ablation was performed 2-4 days after the detection of DF in the second follicular wave PP. OPU was repeated 3-5 times at 3 or 4-day intervals from 3-4 days after the follicular ablation. At OPU, the follicles were enumerated and all those > or = 5 mm in diameter were aspirated. Recovered oocytes were subjected to in vitro maturation and fertilization. Both criteria were similar between ovulated and non-ovulated groups, and between early PP and cyclic groups. These results suggest that FSH/LH secretions required for follicle recruitment and subsequent follicular growth during the early PP period are similar to those after resumption of the estrous cycle. They also indicate that follicular oocytes during the early PP period have developmental competence.