Fertilizability of oocytes derived from Holstein cows having different antral follicle counts in ovaries

Effects of maternal antral follicle count in Bos taurus indicus cattle on the genetic merit of male offspring and antral follicle count of female offspring

This study evaluated the effects of antral follicle count (AFC) in female cattle on offspring characteristics. Recently calved multiparous Bos indicus cows (Nelore; n = 222) were evaluated using ultrasonography on random days of their estrous cycle to determine the AFC and were classified into "low" (≤15 follicles), "intermediate" (≥16 and ≤ 29 follicles), and "high" (≥30 follicles) AFC groups. Weight and scrotal circumference (SC) of male offspring from these cows (n = 127) were determined from 20 to 27 months, and the data were added to a genetic evaluation program (economic total genetic merit, MGTe and TOP value) that uses the kinship matrix to evaluate the genetic relationship between animals. The AFC of female offspring from these cows (n = 95) was evaluated to analyze the relationship between the AFC of mothers and daughters. The effects of maternal AFC on the genetic merit of male and female offspring were analyzed using GLIMMIX and GLM, respectively. Correlations were assessed using the Pearson's coefficient. Male offspring of cows with high AFC had superior MGTe (P = 0.005) and TOP values (P = 0.01) than those from cows with low AFC. Additionally, the AFC of mothers was positively correlated with MGTe (R = 0.33; P < 0.0001) and negatively correlated with TOP values (R = -0.32; P < 0.0001). The SC (P = 0.01), but not body weight of the offspring (P = 0.46) was affected by maternal AFC. The daughters' AFC were correlated (R = 0.29; P = 0.004) with mothers' AFC and were influenced by maternal (P = 0.05) but not paternal (P = 0.77) effect. In conclusion, cows with high AFC produced males with greater MGTe, superior TOP values and higher SC. Maternal AFC did not influence the weight of male offspring but was correlated with the AFC of daughters.

Development of innovative marker detection methods for high-fertility ducks (Anas plastyrhynchos)

We previously analyzed the genome-wide gene expression at the transcription level in pre-hierarchical ovarian follicles (approximate 5 mm in diameter) between two groups of ducks representing high and low fertility. Orthodenticle homeobox 2 (otx2) was identified with significantly differential expression in the high-fertility group versus the low-fertility group. To identify the relationships between genotypes and phenotypes, we recorded the reproductive performance in advance, including fertility, hatchability, and fertile period of female ducks. To ensure coverage of the entire duration of the fertile period, we extended the egg collection period after artificial insemination. Naturally, sperm cannot survive after a certain period of time in the female reproductive tract (sperm is not immortal); therefore, lower average values for fertility were observed in this study than that observed after a normal egg collection period, i.e., the lower average values of fertility (18 days after artificial insemination), were not due to the effect of otx2. The otx2 genomic sequence of Tsaiya ducks was firstly amplified with a primer pair of i3F and i3R for polymerase chain reaction based on Pekin duck sequence and a resultant 444-base pair fragment was obtained for DNA sequencing. Using multiple sequence alignment, new single-nucleotide polymorphisms g.366T > C and g.182G > T were discovered in the otx2 gene. With respect to g.366T > C, ducks were classified into CC, CT, and TT genotypes. For g.182G > T, three genotypes (GG, GT, and TT) were identified. Ducks were genotyped using novel specific primers and probes to rapidly screen their single-nucleotide polymorphisms. The results indicated that ducks with the CC genotype of g.366T > C exhibited the highest fertility among the CC, CT, and TT genotypes (p < 0.05). No significant difference was found in the fertile period and hatchability among three genotypes of g.366T > C. Moreover, no association was found between g.182G > T genotypes and the three reproductive phenotypes examined in this study. Collectively, the otx2 g.366T > C genotype is associated with duck females, and can be used as a marker for farming a flock of ducks with high fertility, as well as for genetic selection of breeders.

Investigating anogenital distance and antral follicle count as novel markers of fertility within a herd of cows with positive or negative genetic merit for fertility traits

Using early-in-life markers of reproductive characteristics may enhance the speed and success of genetic improvement in fertility. We investigated 2 phenotypes that can be measured early in life and are moderately heritable to determine their association with traditional measures of reproductive success and genetic variation under a seasonal-calving, pasture-based system. Cows were bred to be divergent in the New Zealand Fertility Breeding Value, which estimates genetic merit for fertility. Cows consisted of 2 groups with an average positive (+5%) or negative (-5%) genetic merit for fertility traits and were expected to have large diversity in reproductive outcomes. Calves were genotyped at 41 ± 3.1 d of age (mean ± SD; n = 538), and antral follicle counts (AFC) were measured when they were postpubertal heifers before their first breeding (416 ± 15 d old; 92-d range; n = 520). The anogenital distance (AGD) was measured in 478 primiparous cows of this same population 50 to 60 d after the breeding start date when they were 881 ± 25 d old (145-d range). The AGD was shorter in animals with a positive genetic merit for fertility traits (based on parent averages). An indicator of herd reproductive success in a seasonal-calving system (recalving by 6 wk in lactation 2) was chosen for logistic regression with cross-validation, and if significant, a cut-off was calculated that categorized animals into groups. Both linear and quadratic regression was undertaken, and the model with the greatest sensitivity for detection of nonpregnant cows used. The AGD linear model was significant with a sensitivity of 64% and a specificity of 48%. This model resulted in a cut-off of 102 mm, which we used to classify cows as short (≤102 mm) or long (>102 mm) AGD animals. Primiparous cows with a short AGD were more likely to be pregnant within the first 3 and 6 wk of mating, and become pregnant as a primiparous cow, than those with a long AGD. The time from calving to conception was 20 d earlier in short AGD compared with long-AGD cows. None of the models tested for AFC were significant; therefore cows were categorized into 3 groups based on previous work in seasonal systems. However, associations between fertility phenotypes and AFC group were limited. Genomic regions of interest for AGD and AFC did not overlap, indicating phenotypes were genetically independent. Overall, AGD appears as a promising early marker of fertility in seasonal grazing systems.

Antral follicular count and its relationship with ovarian volume, preantral follicle population and survival, oocyte meiotic progression and ultrastructure of in vitro matured bovine cumulus-oocyte complexes

This study aimed to evaluate the relationship between antral follicular count (AFC) and ovarian volume (OV), preantral follicular population and survival, meiotic progression and ultrastructure of cumulus-oocyte complexes (COCs) after in vitro maturation. In experiment 1, the relationship between AFC and preantral follicle population and survival was evaluated by classical histology. In experiment 2, the relationship among AFC, OV, ability of oocytes to resume meiosis and ultrastructure of in vitro matured bovine COCs was studied. A positive correlation (P < 0.05) between AFC and the numbers of healthy primordial, degenerate and total follicles was observed, as well as with healthy secondary follicles and total follicles. The numbers of grades I and II oocytes in ovaries of high AFC class were higher compared with those with intermediate or lower AFC. After in vitro maturation, COCs from ovaries of high AFC had a higher percentage of oocytes in metaphase II compared with those of intermediate and low AFC (P < 0.0001). Ovaries of intermediate AFC had a higher percentage of oocytes in metaphase II compared with ovaries with low AFC (P < 0.0001). The proportion of oocytes in metaphase I, telophase I and anaphase I in COCs from ovaries of intermediate AFC (26.04%) was higher (P < 0.05) compared with that seen in COCs of ovaries with high (8.55%) and low (14.15%) AFC. No differences in the ultrastructure of oocytes were seen. In conclusion, after in vitro maturation, cow ovaries with high AFC have higher numbers of oocytes that reach in metaphase II (MII), but they also have higher numbers of degenerated primordial and primary follicles.

Clinical and structural changes in reproductive organs and endocrine glands of sterile cows

Aim

The study aimed to determine both macroscopic and microscopic changes in the reproductive organs of sterile cows.

Materials and Methods

Careful clinical and gynecological examinations (using histological and histochemical methods) of organs of culled sterile cows, such as ovaries, oviducts, the uterus, pars anterior adenohypophysis, thyroid body, and adrenals, were performed.

Results

It was found that 20% of the examined cows in the farms of the Republic of Bashkortostan had pathology of reproductive organs. Ovarian dysfunction was diagnosed in 31% of sterile cows. Histological and histochemical studies revealed that high atresia of all types of ovarian follicles is associated with hypofunction of the ovaries. This was related to stromal vascular dystrophy and was accompanied by atrophy of thecal endocrine elements, resulting in decrease of endocrine and generative function of ovaries.

Conclusion

Essential elements of the ovarian dysfunction pathogenesis are disorders of the functional system "ovary-pituitary-adrenal-thyroid gland" and the abnormality of utero-ovarian relationships, which differ significantly during hypofunction, in case of follicular cysts, and in case of persistent corpora lutea. This difference in abnormalities of utero-ovarian relationships should be considered when developing diagnostic and treatment methods and determining preventive measures.

Relationships between the antral follicle count, steroidogenesis, and secretion of follicle-stimulating hormone and anti-Müllerian hormone during follicular growth in cattle

BACKGROUND

The antral follicle count (AFC) in mammalian ovaries positively correlates with female fertility. To clarify the causes of differences in fertility between low and high AFC cows, we investigated follicular growth dynamics and hormone concentrations in plasma, follicular fluid, and in vitro growth (IVG) media at different stages of follicular growth.

METHODS

Seven cows were divided into high AFC (n = 4, > 30 follicles) and low AFC (n = 3, < 30 follicles) groups based on the peak AFC detected by ultrasonography. These cows were subjected to estrous synchronization, daily ovarian ultrasonography, and blood collection. Their follicular fluid was collected from dominant follicles at different stages (selection, luteal, and ovulatory phases). In another experiment, we cultured oocyte-cumulus-granulosa cell complexes collected from early antral follicles (< 1 mm) for 12 days. Estradiol-17β (E₂), testosterone (T), progesterone (P₄), and anti-Müllerian hormone (AMH) concentrations in follicular fluids and plasma were measured. Plasma follicle-stimulating hormone (FSH) concentrations were examined. E₂, P₄, and AMH concentrations were also measured in IVG media.

RESULTS

The numbers of small (< 4 mm) and intermediate (4-8 mm) follicles were larger in the high AFC group than in the low AFC group (P < 0.05). The number of intermediate follicles was stable in the low AFC group, indicating consistent development. However, the number of these follicles fluctuated in the high AFC group. Plasma FSH concentrations were higher, whereas E₂ and T concentrations were lower in the low AFC group (P < 0.05). E₂ concentrations and the E₂/P₄ ratio in ovulatory follicles and IVG media on day 8 were higher in the high AFC group (P < 0.05). AMH concentrations in plasma and IVG media (P < 0.01) were higher in the high AFC group.

CONCLUSIONS

The weaker response to FSH of granulosa cells caused low E₂ production in the low AFC group, resulting in high FSH concentrations and the consistent development of intermediate follicles. Conversely, higher E₂ concentrations suppressed FSH secretion in the high AFC group. Granulosa cells in the high AFC group had the ability to produce more AMH than those in the low AFC group throughout IVG culture.

Embryo competence and cryosurvival: Molecular and cellular features

Global cattle genetic market is experiencing a change of strategy, large genetic companies, traditionally recognized in the artificial insemination field, have also begun to operate in the embryo market. Consequently, the demand for in vitro produced (IVP) embryos has grown. However, the overall efficiency of the biotechnology process remains low. Additionally, the lack of homogeneity of post-cryopreservation survival results of IVP embryos still impairing a massive dissemination of this biotechnology in the field. A great challenge for in vitro production labs is to increase the amount of embryos produced with exceptional quality after each round of in vitro fertilization. Herein, we discuss the molecular and cellular features associated with the competence and cryosurvival of IVP embryos. First, morphofunctional, cellular and molecular competence of the embryos were addressed and a relationship between embryo developmental ability and quality were established with cryosurvival and pregnancy success. Additionally, determinant factors of embryo competence and cryosurvival were discussed including the following effects: genotype, oocyte quality and follicular microenvironment, in vitro production conditions, and lipids and other determining molecules. Finally, embryo cryopreservation aspects were addressed and an embryo-focused approach to improve cryosurvival was presented.

Acquisition of developmental competence and in vitro growth culture of bovine oocytes

Recently, the demand of transferable embryos in cattle industry is increasing, and the number of embryos produced in vitro is also increasing in the world. Although oocytes are collected from individual elite cattle by ovum-pick up (OPU) and used for in vitro production (IVP) of embryos, the cattle are mono-ovulatory animal. It means that most of oocytes collected from ovaries are destined to degenerate. To improve the IVP efficiency, we should predict the developmental competence of oocytes correctly and culture them by the suitable way. In addition, in vitro production of bovine oocytes by in vitro growth (IVG) culture system will become a candidate of supply source of oocytes for IVP. If we can produce high competent oocytes by IVG, IVP efficiency will be improved and the genetic improvement of cattle will be dramatically accelerated. In the review, I introduce our researches related to oocyte morphology, the developmental competence, and the production of oocytes having high developmental competence by IVG culture.

Repeatability of antral follicle count according parity in dairy cows

Ovarian reserve in cattle can be predicted by an indicator, the antral follicle count (AFC), which is easily determined via ovarian ultrasonography. However, the repeatability of AFC measurements in the same individual taken approximately 1 year apart after first parity remains unclear. This study, thus, aimed to clarify the between-lactation repeatability of AFC after first parity in dairy cows. We measured the AFC of the same individual cows consecutively across both first and second parity, both second and third parity, and both third and fourth parity in 31, 37, and 26 heads, respectively. The values of the intraclass correlation coefficients (ICC) for the AFCs in first–second and second–third parity cows were more than 0.8, and the value of the ICC for the AFCs in third–fourth parity cows was significantly lower than that in first–second parity cows (P = 0.01). Subsequently, based on the average number of AFCs measured at some points from first to third parity, we classified the cows into three tertiles: <11 (low), 11–15 (intermediate), and ≥ 15 (high). We then compared the reproductive performance of the first through third parity cows among the groups. The hazards of pregnancy by 200 days postpartum were higher in the high group than in the other groups (P < 0.05). Our findings demonstrate that between-lactation repeatability of AFC from first through third parity in dairy cows is very high, and that cows with an AFC of ≥ 15 have a better reproductive performance than cows with a low AFC.

Relationship between the antral follicle count in bovine ovaries from a local abattoir and steroidogenesis of granulosa cells cultured as oocyte-cumulus-granulosa complexes

The antral follicle count (AFC) is used as an indicator of cow fertility. We herein investigated the relationship between AFC and the steroidogenesis of granulosa cells and confirmed the developmental competence of oocytes derived from early antral follicles (0.5–1.0 mm) using in vitro growth culture. Slaughterhouse-derived ovaries were divided into high (≥ 25) and low (< 25) AFC groups based on AFC (≥ 2.0 mm). Oocyte-cumulus-granulosa complexes (OCGCs) collected from early antral follicles were cultured for 12 days. The total number, viability, and diameter of granulosa cells and estradiol-17β and progesterone production during the culture were evaluated. Surviving oocytes on day 12 were subjected to in vitro maturation, and their volume and nuclear status were evaluated. Some oocytes were subjected to the evaluation of developmental competence to blastocysts. Although the total number and viability of granulosa cells did not differ between the groups, granulosa cell diameters were smaller in the high AFC group than in the low AFC group. The estradiol-17β and progesterone ratio on day 8 was higher in the high AFC group than in the low AFC group. Oocyte volumes and nuclear maturation rates were greater in the high AFC group than in the low AFC group. The development rate to blastocysts was 9.1% in the high AFC group, while no oocytes developed to blastocysts in the low AFC group. Therefore, estradiol-17β production by granulosa cells appears to be greater in high AFC cattle than in low AFC cattle, thereby promoting the acquisition of oocyte competence.

The relationship between antral follicle count in a bovine ovary and developmental competence of in vitro-grown oocytes derived from early antral follicles

To clarify the relationship between ovarian reserve and the developmental competence of bovine oocytes, oocyte-granulosa complexes (OGCs) collected from early antral follicles (≤ 1 mm) in ovaries with high (≥ 25) and low (<25) antral follicle counts (AFCs) were used. OGCs derived from different AFC groups were cultured for growth followed by maturation, fertilization and blastocyst formation. Viability of OGCs during growth culture was similar between groups; however, OGCs in the high-AFC group had a larger number of granulosa cells than the low-AFC group at 12 days of growth. The proportion of matured oocytes in the high-AFC group was higher than that in the low-AFC group. Mitochondrial activity of oocytes before maturation in the high-AFC group was higher than that in the low-AFC group; however, accumulation of reactive oxygen species was similar between groups. Cleavage rate in the high-AFC group tended to be higher than that in the low-AFC group, although blastocyst development was similar between groups. In conclusion, oocytes derived from ovaries with high AFC have higher maturational ability and fertilizability than those from low AFC. The difference may be caused by high proliferation of granulosa cells from ovaries with high AFC.