Bovine OPU-derived oocytes can be matured in vitro for 16-28 h with similar developmental capacity.

The aim of this study was to determine the optimal maturation culture period of ovum pick up (OPU)-derived cumulus oocytes complexes (COCs) in relation to their developmental capacity. Embryo production, embryo cryotolerance, post-transfer embryonic survival and calf characteristics such as gestation length, birthweight and sex ratio were investigated. This retrospective study covers the analyses of ovum pick up -in vitro production and calving results from a commercial programme that took place between March 1994 and September 2004. Donors were both heifers (of which approximately 90% pregnant) and cows (of which approximately 10% pregnant). Embryo production analyses were based on 7800 OPU sessions conducted from January 1995 until January 1999. Analyses of calving rate were based on 13 468 embryo transfers performed during January 1995 until May 2002. Analyses on calf characteristics were based on 2162 calves born between March 1994 and September 2004. The in vitro maturation culture period ranged from 16 to 28 h. The mean production rate of transferable embryos was 16.5% (1.2 embryos per OPU session). Length of maturation culture period did not affect the production of transferable embryos. Mean calving rate was 40.9% and 38.7% for fresh and frozen/thawed embryos, respectively. Calving rate was not affected by the maturation culture period. Mean birthweight, gestation length and proportion of male calves were 46 kg, 281.9 days and 52.8%, respectively. Maturation culture period did not affect these variables. In conclusion, this study shows that the in vitro maturation culture period within the range of 16-28 h does not affect in vitro embryo production, embryo cryotolerance, post-transfer embryonic survival and calf characteristics, suggesting that all COC batches collected by OPU on the same day, can be fertilized in one IVF session without a significant loss in the production from oocyte to calf.

What affects fertility of sexed bull semen more, low sperm dosage or the sorting process?

Until now it has been unclear to what extent the reduced fertility with sexed semen in the dairy industry is caused by too few sperm per AI dose, or by the effect of flow cytometric sorting, which is the established procedure for sexing semen. Therefore, we evaluated the effects of low sperm numbers per dose with and without sorting on non-return rates after 56 days (NRR 56); in addition, we evaluated the effects of bulls, in order to further optimize use of sexed semen. Based on results of using sexed semen from seven Holstein bulls, an overall numerical decline of 13.6% in NRR 56 was observed (P<0.05). About two-thirds of this decline (8.6%) was due to the low dose (P<0.05), and a third (5.0%) due to the process of sorting (P<0.05). The effect of low dosage and sorting differed among bulls. We observed a sex ratio of 91.6% females for sexed semen from the first 131 calves born. Currently the best way to increase fertility of sexed semen is by closely monitoring fertility so that the highest fertility bulls are used, and by improving farm animal management. However, to make substantial progress, more in depth studies are needed on the sexing technology, especially on aspects such as sorting procedures and sperm dosage.

Carbon-activated gas filtration during in vitro culture increased pregnancy rate following transfer of in vitro-produced bovine embryos.

Many environmental conditions for in vitro embryo production (IVP) systems for cattle have been relatively standardised, e.g. media composition, temperature, pH, water quality, and atmospheric composition. However, little attention has been paid to the quality of ambient laboratory air and the gas environment in incubators. Although a few studies have examined the effects of chemical air contamination on IVP of human embryos, there are no published accounts for domestic animal embryos. Therefore, this study investigated the effects of an intra-incubator carbon-activated air filtration system (CODA) during in vitro culture (IVC) on embryonic development and subsequent pregnancy rate of bovine embryos. Immature cumulus-oocyte-complexes (COCs) were obtained twice-weekly by ultrasonic-guided transvaginal oocyte aspiration. The COCs were matured in TCM199/FCS/LH/FSH, fertilized with frozen-thawed Percoll-separated semen, and subsequently cultured for 7 day in SOFaaBSA. Day 7 embryos were transferred either fresh or frozen/thawed. The experimental design was a 2 x 2 factorial; presumptive zygotes were placed either in a conventional CO(2)-O(2)-N(2) incubator (Control group) or in an identical CO(2)-O(2)-N(2) incubator with a CODA intra-incubator air purification unit (CODA group) for IVC. The embryo production rate at Day 7 was not affected by the CODA air purification unit (23.4 and 24.7% morulae and blastocysts per oocyte for control and CODA, respectively) nor was there any significant effect on embryo stage or quality. However, the pregnancy rate was improved (P=0.043) for both fresh (46.3% versus 41.0%) and frozen/thawed embryos (40.8% versus 35.6%). In conclusion, atmospheric purification by the CODA intra-incubator air purification unit significantly increased pregnancy rate following transfer of in vitro-produced bovine embryos.

Effects of different reproduction techniques: AI MOET or IVP, on health and welfare of bovine offspring.

Since the introduction of in vitro production (IVP) of bovine and sheep pre-implantation embryos, increased birth weights and other deviations of IVP calves and lambs compared with AI or MOET offspring have been reported. Study 1 of the present paper, a comparison between AI, MOET and IVP (co-culture/serum) calves with respect to calf and calving characteristics in large-scale field conditions, confirms these reports. In addition, it is shown that MOET calves tend towards higher birth weights and have significantly longer gestations and more difficult calvings than AI calves. It is presently unknown if the effect of IVP is also observed later in life. In this paper, data on reproduction characteristics of bovine IVP co-culture/serum offspring are presented. Semen production--and non return data of one year old IVP bulls and superovulation-, AI- and OPU/IVP results of one year old IVP heifers are compared with those of one year old AI and MOET animals producing semen or embryos in the same time period. So far, there are no indications that the use of IVP is reflected in deviate reproduction characteristics of bovine IVP offspring. It has been suggested that use of co-culture cells and serum during in vitro culture of bovine (and sheep) embryos may partially explain the increased birth weights and other deviations of bovine and sheep IVP offspring. Deletion of these factors in semi-defined culture media, e.g. Synthetic Oviductal Fluid (SOF), could result in more normal offspring. Study 2 investigates this hypothesis in both field conditions (Study 2a, comparing AI, IVP co-culture/serum and IVP SOF calves) and in semi-standardized conditions (Study 2b, comparing MOET, IVP co-culture/serum and IVP SOF calves at one herd). In Study 2a, although IVP SOF calves showed (non-significant) shorter gestations, easier calvings and lower percentages of perinatal mortality and congenital malformations than IVP co-culture calves, birth weights were not decreased. In Study 2b however, the difference between IVP co-culture and IVP SOF calves in birth weight and ease of calving was significant (P < 0.05), IVP SOF calves resembling MOET calves more. IVP calves differed significantly from MOET calves with respect to several physiological parameters, such as blood oxygen saturation level, heart beat frequency and some measures of the heart. In addition, in Study 2b, recipients receiving an IVP SOF embryo showed a more regular return to estrus than those receiving an IVP co-culture embryo. From Study 2 it can be concluded that using a semi-defined medium for in vitro culture (SOF) may improve characteristics of IVP calves born.

Effect of different stages of the follicular wave on in vitro developmental competence of bovine oocytes.

This study aimed to investigate the developmental competence of ovum pick-up collected oocytes on three stages of the follicular wave: Days 2, 5 and 8. A group of 11 cows was used in successive cycles to perform ovum pick-up on either Day 2, 5 or 8 of an induced follicular wave (three sessions per stage). Follicular waves were initiated by puncturing the dominant follicle and all other follicles sized > or = 5 mm at Days 5-7 of the cycle. The plasma progesterone concentrations did not differ between the days of ovum pick-up: 4.0 +/- 1.8, 5.1 +/- 1.6 and 5.2 +/- 1.7 ng/ml for Days 2, 5 and 8, respectively. The proportion of oocytes with three or more layers of non-expanded cumulus cells was higher for Day 5 than Day 8, while Days 2 and 5 did not significantly differ from each other (85, 96 and 68% of 113, 60 and 101 oocytes for Days 2, 5 and 8, respectively). The proportion of oocytes competent to develop a blastocyst in an in vitro production system was higher for Days 2 and 5 than for Day 8: 27, 29 and 15% for the oocytes with fair to good cumulus investment and 23, 27 and 11%, respectively, when all oocytes were taken in account. This indicates that the dominant follicle reduces the developmental competence of oocytes from subordinate follicles at a relatively late stage of dominance. This finding has practical consequences for the handling of cows that undergo ovum pick-up only once or very irregularly. The embryo yield can then be improved by performing the ovum pick-up at Days 2-5 of the cycle or 2-5 days after ablation of the large follicles.

Factors affecting oocyte quality and quantity in commercial application of embryo technologies in the cattle breeding industry.

With the introduction of multiple ovulation, embryo recovery and transfer techniques (MOET) plus embryo freeze-thaw methods in the early 1980s, the breeding industry has the tools in hand to increase the number of calves from donors of high genetic merit. In the early 1990s, the introduction of ovum pick-up followed by in vitro embryo production (OPU-IVP) opened up even greater possibilities. Using these technologies, we challenge biological mechanisms in reproduction. Where normally one oocyte per estrous cycle will develop to ovulation, now numerous other oocytes that otherwise would have degenerated are expected to develop into an embryo. Completion of oocyte growth and pre-maturation in vivo before final maturation both appear to be essential phases in order to obtain competence to develop into an embryo and finally a healthy offspring. In order to increase oocyte quality and quantity in embryo production technologies, current procedures focus primarily on improving the homogeneity of the population of oocytes with regard to growth and state of pre-maturation at the start of a treatment. In the case of MOET, dominant follicle removal (DFR) before superovulation treatment improves the number of viable embryos per session from 3.9 to 5.4 in cows but not in heifers and a prolonged period of follicle development obtained by preventing release of the endogenous LH surge increases the number of ova but not the number of viable embryos per session. In the case of OPU-IVP, the frequency of OPU clearly affects quantity and quality of the collected oocytes and FSH stimulation prior to OPU every 2 weeks resulted in 3.3 embryos per session. Analysis of 7,800 OPU sessions demonstrated that the oocyte yield is dependent on the team, in particular, the technician manipulating the ovaries. It is concluded that an increased understanding of the processes of oocyte growth, pre- and final maturation will help to improve the efficiency of embryo technologies. However, somewhere we will meet the limits dictated by nature.

Improving the resolution of cryopreserved X- and Y-sperm during DNA flow cytometric analysis with the addition of Percoll to quench the fluorescence of dead sperm.

The most effective method to control the sex of offspring is by separating X- from Y-bearing sperm on the basis of their DNA content. Sperm can be stained with Hoechst 33342 and efficiently sexed using a flow cytometer/cell sorter. However, applying this established assay to cryopreserved bovine sperm presents specific problems, such as broad fluorescence distributions without a distinct X- and Y-peak. Our results indicate that these problems are mainly caused by the large amount of dead sperm normally present in a thawed sperm population. We showed that Percoll quenches the fluorescence of chromatin stained with Hoechst 33342 and that this quenching can be applied to reduce the fluorescence of dead sperm. We used this finding to exclude the dead sperm from the sorting window and thus obtained narrower fluorescence distributions and sorted X- and Y-bearing sperm populations containing up to 85 to 92% viable sperm. The viability of the sorted sperm was monitored by propidium iodide exclusion.

Cysteamine supplementation during in vitro maturation of slaughterhouse- and opu-derived bovine oocytes improves embryonic development without affecting cryotolerance, pregnancy rate, and calf characteristics.

Optimization of ovum pick up (OPU) followed by in vitro embryo production (IVP) is strongly driven by the needs of both beef and dairy cattle breeders to enhance genetic improvement. The rapidly growing use of genomic selection in cattle has increased the interest in using OPU-IVP technology to increase the number of embryos and offspring per donor, thus allowing enhanced selection intensity for the next generation. The aim of this study was to optimize embryo production through supplementation of cysteamine during in vitro maturation (IVM) and in vitro culture (IVC) of both slaughterhouse- and OPU-derived oocytes. The effects on embryo production and on embryo cryotolerance, post-transfer embryo survival, and calf characteristics, including gestation length, birth weight, perinatal mortality, and sex ratio were studied. In study 1, immature slaughterhouse-derived cumulus-oocyte complexes (COCs) were matured in IVM medium supplemented with or without 0.1 mM cysteamine, fertilized and cultured for 7 days in 0.5 ml SOFaaBSA. In study 2, cysteamine was present during both IVM (0.1 mM) and IVC (0.01, 0.05, 0.1 mM) from Days 1 to 4. In study 3, OPU-derived COCs were matured in medium supplemented with or without 0.1 mM cysteamine in a 2 × 2 factorial design (OPU week and cysteamine treatment). Embryos were evaluated for stage and grade on Day 7 and, depending on the number of transferable embryos and recipients available, the embryos were transferred either fresh or frozen-thawed at a later date. The presence of cysteamine during IVM significantly increased the embryo production rate with slaughterhouse-derived COCs (24.0% vs. 19.4%). The higher number of embryos at Day 7 was due to an increased number of blastocysts, whereas the distribution of embryos among different quality grades and cryotolerance was not affected. Embryo production rate was negatively affected when cysteamine was present during both the processes of IVM and IVC during Days 1 to 4 of culture (13.2%-19.3% vs. 26.4%). The presence of cysteamine during IVM of OPU-derived COCs also significantly increased the embryo production rate (34.4% vs. 23.4%). The higher number of embryos was again totally due to an increased number of blastocysts, whereas cryotolerance was not affected. The relative increase in embryo production rate was higher with OPU-derived oocytes compared with slaughterhouse-derived COCs (47% vs. 24%). This improvement resulted in a mean of 1.73 transferable embryos per OPU session compared with 1.06 in the absence of cysteamine. The presence of cysteamine did not affect pregnancy rate, gestation length, birth weight, perinatal mortality, and sex of calves born from either fresh or frozen-thawed embryos. This study reported that cysteamine supplementation during IVM greatly improved the efficiency and affectivity of an OPU-IVP program.

Genetic parameters for oocyte number and embryo production within a bovine ovum pick-up-in vitro production embryo-production program.

Genetic factors influencing the outcome of bovine ovum pick-up-in vitro production (OPU-IVP) and its relation to female fertility were investigated. For the first time, genetic parameters were estimated for the number of cumulus-oocyte complexes (Ncoc), quality of cumulus-oocyte complexes (Qcoc), number and proportion of cleaved embryos at Day 4 (Ncleav(D4), Pcleav(D4)), and number and proportion of total and transferable embryos at Day 7 of culture (Nemb(D7), Pemb(D7) and NTemb(D7), PTemb(D7), respectively). Data were recorded by CRV (formally Holland Genetics) from the OPU-IVP program from January 1995 to March 2006. Data were collected from 1508 Holstein female donors, both cows and pregnant virgin heifers, with a total of 18,702 OPU sessions. Data were analyzed with repeated-measure sire models with permanent environment effect using ASREML (Holstein Friesian). Estimates of heritability were 0.25 for Ncoc, 0.09 for Qcoc, 0.19 for Ncleav(D4), 0.21 for Nemb(D7), 0.16 for NTemb(D7), 0.07 for Pcleav(D4), 0.12 for Pemb(D7), and 0.10 for PTemb(D7). Genetic correlation between Ncoc and Qcoc was close to zero, whereas genetic correlations between Ncoc and the number of embryos were positive and moderate to high for Nemb(D7) (0.47), NTemb(D7) (0.52), and Ncleav(D4) (0.85). Genetic correlations between Ncoc and percentages of embryos (Pcleav(D4), Pemb(D7), and PTemb(D7)) were all close to zero. Phenotypic correlations were in line with genetic correlations. Genetic and phenotypic correlations between Qcoc and all other traits were not significant except for the phenotypic correlations between Qcoc and number of embryos, which were negative and low to moderate for Nemb(D7) (-0.20), NTemb(D7) (-0.24), and Ncleav(D4) (-0.43). Results suggest that cumulus-oocyte complex (COC) quality, based on cumulus investment, is independent from the total number of COCs collected via OPU and that in general, a higher number of COCs will lead to a higher number of embryos produced. The correlation between the estimated breeding values for Ncoc and PTemb(D7) of sires in this study and the sires breeding index for female-fertility based on the Dutch cattle population was close to zero. This study revealed OPU-IVP traits (Nemb(D7), NTemb(D7), and Ncoc) that could be of potential value for selection. Introduction of such traits in breeding programs would enhance the number of offspring from superior donors as well as improve the cost efficiency of OPU-IVP programs.

Ways to improve the biosecurity of bovine semen.

Semen production and trade is a worldwide industry. A framework, based on international standards is awaiting international and national regulation. In the perspective of biosecurity of the final product, critical notes can be made according to the semen production regulation and product safety. Process description brings the obligatory health standards for the production bulls, collection and processing of semen, identification, registration, worldwide distribution and insemination into discussion. Test frequency, test quality and demands, way of sampling and test consistency can influence product safety. New scientific knowledge can influence the value of the regulation. Whether a country is free of notifiable disease should influence decisions regarding necessary tests for the production bulls. The biosecurity of the semen production process is influenced by several factors. The effectiveness of the antibiotics used is questionable. The extenders for cryopreservation added to the semen can affect product safety. The way materials and storage containers have to be disinfected must be clear. In modern industry, tracking and tracing is an important issue. Worldwide differences in ways of identification of straws do not benefit a proper identification and registration throughout the process. Regulation could help improve the transparency of production and trade. Before anything concerning biohazard is implemented in regulation, each rule should be thoroughly based on scientific research where possible and furthermore it must be possible to enforce the regulation. The effort it takes to enforce the regulation should be in balance with the benefit it provides. An approach to alter regulation quickly is advisable. To produce a safe product that is accepted for international trade is of vital interest for the survival of artificial insemination (AI) in cattle.