Comparative evaluation of the cost and efficiency of four types of sexing methods for the production of dairy female calves.

This study was conducted to evaluate and compare the economic benefits of different embryo sexing methods, based on the cost per female dairy calf produced. Female calves were produced from four kinds of female embryos: (1) those collected from superstimulated donors at 7-8 days after artificial insemination (AI) with X-sorted semen; (2) those sex-determined by loop-mediated isothermal amplification assay of a biopsy sample of embryos collected from superstimulated donors after AI with conventional unsorted semen; (3) those obtained by invitro embryo production (IVEP), using X-sorted semen and in vitro-matured oocytes collected from donors by ovum pick-up (OPU); and (4) those obtained by IVEP, using X-sorted semen and oocytes collected by OPU after dominant follicle ablation and follicle growth stimulation of the donors. The respective productivities of female calves per technical service and the total production cost per female calf of each sexing method were compared. The production cost per female calf (66,537 JPY), as calculated from the number of female calves per service (1.30), pregnancy rate of transfer (42.9%), rate of female calves obtained (92.9%), and total cost of the method (56,643 JPY plus embryo transfer fee), was less for IVEP with X-sorted semen and follicular growth-stimulated (FGS) oocytes than for the other groups (P < 0.05). The results demonstrate that embryo production with X-sorted semen and FGS oocytes provides a more efficient method for producing female calves than the other embryo sexing methods.

Economic evaluation of artificial insemination of sex-sorted semen on a Brown Swiss dairy farm-A case study.

Artificial insemination using sex-sorted semen is employed to efficiently increase the number of female dairy calves born. Previous studies have determined that using sex-sorted semen is beneficial to improve the management, but the mechanism by which it increases cattle numbers through objective indices of breeding remains unclear. This study focused on a Brown Swiss cattle herd in which frozen female sex-sorted semen was systematically employed to increase the number of cattle. We analyzed the correlation between the increase in the number of cattle and the screening accuracy of sex-sorted semen, measuring indices such as pregnancy rate and birth rate of female calves. Study revealed that: (1) production cost for female calves is influenced by the pregnancy rate, rate of female calves, and using sex-sorted semen is less expensive than using nonsorted semen; (2) improvements in screening accuracy nearly doubled the number of cows and tripled the number of heifers in 5 years; and (3) use of sex-sorted semen improved milk quality. The pregnancy rate was lower when sex-sorted semen was used, but the birth rate of heifers was improved. Results suggest that artificial insemination using sex-sorted semen is beneficial because it economically produces offspring to increase the herd.

Vitrification for bovine embryos with low-quality grade.

This study was conducted to examine the utility of vitrification for bovine embryos with low-quality grade, and simple cryoprotectants dilution method for practitioners. In Experiment 1, survival of frozen embryos was compared with that of vitrified embryos using minimum volume cooling (MVC). Then, vitrified embryos were used to confirm the optimum sucrose concentration in Experiment 2. The survival rates of embryos that had been vitrified following diluted cryoprotectants with the one-step in-straw method were compared with those of fresh control embryos in Experiment 3. Frozen-thawed or vitrified-warmed blastocysts were cultured with TCM-199 supplemented with 100 µmol/L beta-mercaptoethanol +5% fetal bovine serum at 38.5°C in an atmosphere of 5% CO2 in air, their survival after 24 hr were compared. The development to term of fair quality in vivo embryos after vitrification was examined in Experiment 4. Results show that survival rates of frozen-thawed embryos were lower (p < .05) than that of vitrified-warmed ones. When vitrified embryos were warmed in 0.3 mol/L sucrose in straws, their survival rate was 100%. The total cell numbers of vitrified-warmed embryos were comparable to those of fresh control embryos. The six calves from 13 vitrified embryos were delivered in Experiment 4. These results indicate that MVC vitrification following one-step cryoprotectants dilution is utilized to preserve low-quality bovine embryos.

Anesthetic effects of a combination of medetomidine, midazolam and butorphanol on the production of offspring in Japanese field vole, Microtus montebelli.

Pentobarbital sodium (Somnopentyl) can induce surgical anesthesia with a strong hypnotic effect that causes loss of consciousness. Animals have been known to die during experimental surgery under anesthesia with Somnopentyl, causing it to be declared inadequate as a general anesthetic for single treatment. An anesthetic combination of 0.3 mg/kg medetomidine, 4.0 mg/kg midazolam and 5.0 mg/kg butorphanol (M/M/B:0.3/4/5) was reported to induce anesthesia for a duration of around 40 min in ICR mice; similar anesthetic effects were reported in both male and female BALB/c and C57BL/6J strains of mice. However, the anesthetic effects of this combination in Japanese field vole, Microtus montebelli, remain to be evaluated. In the present study, we assessed the effects of Somnopentyl and different concentrations of anesthetic combination (M/M/B:0.3/4/5, 0.23/3/3.75 or 0.15/2/2.5) in Japanese field voles, by means of anesthetic scores. We also examined effect of these anesthetics on production of offspring. Death of the animals was observed only with Somnopentyl. The anesthetic score of Somnopentyl was lower than those of the other anesthetics, although there were no significant differences in duration, body weight and frequency of respiratory among the evaluated anesthetics. Abortion rate with Somnopentyl was significantly higher than that with the M/M/B:0.23/3/3.75 combination, although there was no significant difference in the number of offspring between two. In conclusion, results of this study provide basic information for achieving appropriate anesthetic concentrations in addition to indicating a new, safe and effective surgical anesthetic for Japanese field voles.

Establishment of superovulation procedure in Japanese field vole, Microtus montebelli.

Japanese field vole (Microtus montebelli) is a wild-derived rodent and have unique characteristic. Thus, these species have been expected as model animal. This study was performed to develop novel superovulation procedure for Japanese field vole. First, when 30 IU pregnant mare's serum gonadotropin (PMSG) and 30 IU human chorionic gonadotropin (hCG) were administrated 48 hours apart, females showed higher response to hCG compared with three concentrations of PMSG. Second, to effectively induce ovulation on females after vaginal opening, they were mated with vasectomized male instead of hCG administration. Average number of ovulated oocytes using PMSG mating (13.9 ± 1.9 oocytes) was higher than PMSG-hCG (control; 6.9 ± 2.3 oocytes) or PMSG-hCG mating (6.8 ± 0.8 oocytes). Finally, we attempted superovulation using GnRH agonist (GnRHa). With this treatment, we speculated that GnRHa might induce endogenous luteinizing hormone releasing to cause ovulation. Such superovulation was performed with 30 IU PMSG and different concentration of 20% polyvinylpyrrolidone-GnRHa (15, 30, 45, and 60 µg/kg). As results, average number of ovulated oocytes was highest with 30 µg/kg GnRHa (14.5 ± 4.1 oocytes). The numbers of ovulated oocytes of other concentrations were 5.0 ± 1.4 (15 µg/kg), 12.8 ± 2.7 (45 µg/kg), and 8.8 ± 3.7 oocytes (60 µg/kg). Nuclear status of most collected oocytes was the second meiotic division (range, 94.3%-100%). These superovulation procedures will be useful for development of in vitro culture systems and assisted reproductive technologies for not only Japanese field vole but also other voles.

Intrauterine embryo transfer with canine embryos cryopreserved by the slow freezing and the Cryotop method.

Canine embryos (8-cell to blastocyst stages) frozen-thawed using the slow-freezing method with glycerol (four recipients) or dimethyl sulfoxide (three recipients) as a cryoprotectant and vitrified-warmed using the Cryotop method (five recipients) were surgically transferred into the unilateral uterine horn of recipient bitches. As a result, the morphology of embryos frozen-thawed using the slow-freezing method was judged to be normal, but no conception occurred in any of the recipient bitches. Two of the five bitches that received transferred embryos (morula to early blastocyst stages) vitrified-warmed using the Cryotop method became pregnant and produced normal pups (1/9 embryos, 11.1% and 1/6 embryos, 17.0%). It was concluded that the Cryotop method was more appropriate for canine embryo cryopreservation than the slow-freezing method, which is used for the cryopreservation of embryos of other mammalian species.

Development of bovine oocytes reconstructed with a nucleus from growing stage oocytes after fertilization in vitro.

The developmental capacity of reconstructed bovine oocytes that contained nuclei from growing stage oocytes, 70-119 microm in diameter, was assessed after fertilization in vitro. Nuclei from growing stage oocytes of adult ovaries were transferred to enucleated, fully grown germinal vesicle (GV) stage oocytes. After culture in vitro, the reconstructed oocytes matured, forming the first polar body and MII plate. To supply the ability to form pronuclei, the resultant MII plate was transferred to enucleated MII oocytes, which were obtained by in vitro culture of cumulus-oocyte complexes. After fertilization in vitro, 11-15% of the reconstructed oocytes developed to morulae and blastocysts. To assess the ability to develop to term, a total of 27 late morulae and blastocysts were transferred to 19 recipient cows. Of the three cows that subsequently became pregnant, one recipient, who received two embryos derived from reconstructed oocytes with a nucleus from oocytes 100 to 109 microm in diameter, continued the pregnancy to Day 278 of gestation. This pregnancy, however, was unexpectedly a triplet pregnancy that included a set of identical twins and resulted in the premature birth of the calves, followed by death from lack of post-parturient treatment. These results show that bovine oocyte genomes are capable of supporting term development before the oocytes grow to their full size, which suggests that growing stage oocytes can be directly used as a source of maternal genomes.

Relation of reproductive performances and rectal palpation for luteum function of heifers 7 days after estrus.

Diagnosis of corpus luteum (CL) function by rectal palpation (RP) has been widely used for recipient selection of embryo transfer (ET), a technology essential for genetic improvements in cattle. To examine the accuracy of RP diagnosis method, the relationship between RP-based CL function and reproductive performance was compared in this study. In Experiment 1, CL of Holstein heifers on day 7 after estrus was classified into functional or hypoplastic by RP, and the results were compared with ultrasonographic (US) images and plasma progesterone (P4) levels. As a result, heifers with functional CL judged by RP had a mean maximum CL diameter of 20.1 ± 3.1 mm on US and a mean P4 concentration of 8.1 ± 2.3 ng/mL. These values were significantly greater than those of heifers with hypoplastic CL (12.4 ± 5.4 mm, 4.0 ± 2.8 ng/mL) (P < 0.001). In Experiment 2, the length of the estrus cycle was examined between functional CL and hypoplastic CL. The rate of heifers with a normal estrus cycle length with 18-25 days was significantly lower with hypoplastic CL than with functional CL (16/24 vs. 43/46, P < 0.01). In Experiment 3, 543 inseminated heifers were similarly classified by CL function by RP 7 days after estrus. The heifers with functional CL showed higher pregnancy rate compared with the heifers with hypoplastic CL (75.2 vs. 47.9%, P < 0.0001). Finally, the CL function of 66 heifers was examined by RP on day 7 post-estrus, and ET was performed in 49 (74.2%) heifers with functional CL. As a result, 27 (55.1%) of them became pregnant. Taken together, these results reconfirm that RP on day 7 after estrus is useful for selection of heifers with functional CL.

Effect of estrus synchronization treatment after luteolysis on Holstein heifers as embryo transfer recipients.

This study was designed to evaluate the effect of estrus synchronization treatments on recipient heifers for embryo transfer (ET). Holstein heifers were separated into the following three groups: (i) an administration of 50 µg GnRH (gonadotropin-releasing hormone) analog was given to heifers at a random stage of the estrus cycle, followed 7 days later by two administrations of 7.5 mg prostaglandin F2 alfa analog (PG) as control; (ii) another administration of 100 µg GnRH was given to the control group at 48 h after the administration of PG as the second GnRH group; and (iii) an administration of 0.75 mg estradiol benzoate (E2) was given to the control group at 24 h after the administration of PG as the E2 group. Each method caused estrus synchronization. Fresh embryos were nonsurgically transferred into the suitable recipients that had a functional corpora lutea (CL) 7 days after estrus. The E2 group showed a significantly higher (P < 0.01) rate of estrus synchronization (98.9%) at 1-3 days after PG administration and the final pregnancy rate of the E2 group (50.6%) was also significantly higher than the other groups (37.1%, P < 0.05 and 30.9%, P < 0.01, respectively). These findings demonstrate that E2 administration 24 h after PG protocol is effective for estrus synchronization of Holstein heifers, thus improving the productivity of ET.

Classification of morphological changes based on the number of cleavage divisions in bovine embryos.

Quantification based on cleavage division (CD) of bovine preimplantation embryos facilitates quantitative analyses of embryonic developmental processes because CD occurs roughly once each day for all blastomeres for up to at least 9 days after ovulation. Therefore, embryonic morphological changes during this period were classified according to CD number. In this study, embryos collected from superovulated donors 0-9 days after ovulation were first classified morphologically into 14 conventional developmental stages. The total cell numbers (TCN) of embryos were measured using the air-dry method. The respective CD numbers of the embryos were then determined using logarithmic transformation of the TCN. The CD numbers of embryos were increased 0-10th with 11 stages. The 0th CD corresponded to 1-cell stage embryos; the 1st CD corresponded to 2-cell stage embryos; the 2nd CD corresponded to 3-4-cell stage embryos; the 3rd CD corresponded to 5-8-cell stage embryos; the 4th CD corresponded to 9-16-cell stage embryos, the 5th CD corresponded to morulae (17-32-cell stage embryos); and the 6th CD corresponded to the compact morulae. Furthermore, the 7th CD included early blastocysts to blastocysts. The 8th CD included expanded, collapsed and hatching blastocysts. The 9th CD included hatched blastocysts. The 10th CD included expanding-hatched blastocysts. The relationship between the CD number and the morphological characteristics of the bovine embryos 0-9 days after ovulation was expressed using a linear equation, and this revealed a high degree of correlation (y=0.98x-0.96, r=0.99). These results suggest that morphological changes of bovine embryos can be classified accurately using an 11-stage classification system based on the number of cleavages.

Transition of cell numbers in bovine preimplantation embryos: in vivo collected and in vitro produced embryos.

The total cell numbers (TCNs) of bovine embryos collected from superovulated donors (VIVO embryos) were counted 0-9 d after ovulation to quantify the developmental process. Using numerical analysis of embryo development, we also compared the developmental process of VIVO embryos, in vitro-fertilized (IVF) embryos and nuclear transfer (NT) embryos obtained from enucleated oocytes and blastomere nuclei. The TCNs of embryos were measured using the air-dry method. Cleavage divisions (CD) of the embryos were obtained using logarithmic transformation of the TCN. The TCN of the VIVO embryos increased significantly (P<0.001) with time. The relationship between the CD of the VIVO embryos at 0-9 d after ovulation and age in days was described by a linear equation with a high correlation (y=1.03x+0.16, r=0.99), showing that CD occurs about once each day for all blastomeres. However, compared to the VIVO embryos, the TCN of the IVF embryos did not increase from 3-4 d nor after 7 d; the TCN of the NT embryos did not increase after 7 d (P>0.05). The results suggest a delay in development at these developmental stages. The slopes of regression lines of the IVF and NT embryos were significantly (P<0.001) smaller, indicating that quantification of the developmental process of VIVO embryos according to TCN and CD would be useful as criteria for numerical evaluation of the developmental process of bovine in vitro produced embryos.

Application study of developmental engineering for livestock production.

This paper describes several technical improvements in developmental engineering for livestock production, including their practical utility in the field. The artificial production of monozygotic twins via embryo splitting is shown to increase embryo productivity, while embryo sexing capability provides added value without compromising offspring productivity, with both techniques being adequate for practical field applications. It is also shown that: (1) the development of nuclear transfer utilizing oocytes collected from slaughtered ovaries and matured in vitro enables producing a large number of cloned embryos, (2) the intracytoplasmic injection of somatic cell improves the productivity of nuclear transplantation, and (3) the injection of sperm increases the rate of normal oocytes with male and female pronuclei allowing further preimplantation development. Finally, the removal of cytoplasmic lipid droplets from embryos following centrifugation alters an embryo's intrinsic sensitivity to low temperature allowing long-term preservation. Collectively, these techniques have clearly provided improvements in developmental engineering for livestock production.

Improved survival of vitrified in vivo-derived porcine embryos.

An efficient cryopreservation protocol for porcine morulae was investigated with three types of vitrification having different cooling rates (Exp. 1). Survival of embryos vitrified after removal of cytoplasmic lipid droplets was also examined by means of the minimum volume cooling (MVC) method (Exp. 2). In Exp. 1, the morula stage embryos were vitrified with a 0.25 ml plastic straw (ST-method), gel loading tip (GLT-method) and the MVC-method, respectively, and stored in liquid nitrogen after which they were warmed in sucrose solutions with cryoprotectants being subsequently removed in a stepwise manner. In Exp. 2, morulae were centrifuged with 7.5 microg/ml cytocharasin B at 12000 x g for 20 min to polarize the cytoplasmic lipid droplets that were then removed from the embryos by micromanipulation (delipation). Both those delipated at the morula stage and the intact embryos at the morula to blastocyst stages were vitrified by the MVC-method. In vitro survival of the vitrified embryos was assessed in both experiments by culturing in NCSU-23 + 10% FCS for 48 h. In vitro developments of vitrified embryos after warming to blastocysts were 20% (6/30) for the ST-method, 39% (18/46) for the GLT-method, and 60% (26/43) for the MVC-method. Embryo survival was further improved by vitrification after delipation (95%, 35/37) compared to intact vitrified morulae (24/42, 57%, P<0.001) and blastocysts (23/31, 74%, P<0.05). Moreover, the number of cells in blastocysts (92 +/- 25) derived from the delipated-vitrified morulae was comparable to those derived from intact control non-vitrified embryos (103 +/- 31). Our results demonstrate that vitrified porcine morulae have the highest survival when using the MVC-method in conjunction with delipation.

Cryopreservation of porcine embryos derived from in vitro-matured oocytes.

This study describes a cryopreservation method for porcine in vitro-produced (IVP) embryos using as a model parthenogenetic embryos derived from in vitro-matured (IVM) oocytes. IVP embryos at the expanded blastocyst stage were cryopreserved by vitrification using the minimum volume cooling (MVC) method and exhibited an embryo survival rate of 41.2%. Survival was then significantly improved (83.3%, P < 0.05) by decreasing the amount of cytoplasmic lipid droplets (delipation) prior to vitrification. IVP embryos at the 4-cell stage also survived cryopreservation when vitrified after delipation (survival rate, 36.0%), whereas post-thaw survival of nondelipated embryos was quite low (9.7%). Furthermore, it was demonstrated that porcine IVP morulae can be cryopreserved by vitrification following delipation by a noninvasive method (survival rate, 82.5%). These results clearly confirm that porcine embryos derived from IVM oocytes can be effectively cryopreserved with high embryo survival using the MVC method in conjunction with delipation.