Interstrain inseminations and embryo transfers between the SLA miniature pig and standard crossbred pig

Oestrous synchronization, ovarian superovulation and intraspecific transfers from a closed breeding colony of inbred SLA miniature pigs

The inbred SLA miniature pig is a unique animal model developed for organ transplantation studies and pre-clinical experimental purposes. Reported oestrous synchronization and superovulation treatments were examined in two SLA haplotypes (AA and DD) to allow collection of embryos for both practical embryo transfer and experimental technologies from a closed breeding colony. Pre-puberal miniature pigs were poor responders to oestrous synchronization treatments, while post-puberal sows were equivalent to commercial sows. Following superovulation, the ovulation number (corpora .hemorrhagica) was higher (p < 0.05) in the cycling sows when compared with non-cycling sows. Ovulations were equivalent to commercial pre-puberal gilts and non-cycling sows (p > 0.05). No difference in ovulation number between haplotypes was observed, which differs from the previous report (DD>AA). Collection of zygotes for pronuclear injection was the highest in the non-cycling post-puberal miniature pig group (p < 0.05), although significantly lower when compared with the commercial pig treatment groups (p < 0.05). The incidence of cystic endometrial hyperplasia in our colony was equivalent to rates observed in commercial pigs. Pronuclear visualization following centrifugation was the highest in the non-cycling miniature sow group and approximates to about 25% of ovulations and about half the rate observed in the commercial pigs (50%). Miniature pig embryos transferred between SLA haplotypes and transfer of DD embryos to commercial pigs resulted in live births at a higher efficiency than previously reported. This study demonstrates the feasibility of undertaking assisted reproductive technologies in a closed breeding colony of inbred SLA miniature pigs without compromise to the breeding programmes.

Production of transgenic and non-transgenic clones in miniature pigs by somatic cell nuclear transfer

Miniature pigs have been recognized as valuable experimental animals in various fields such as medical and pharmaceutical research. However, the amount of information on somatic cell cloning in miniature pigs, as well as genetically modified miniature pigs, is much less than that available for common domestic pigs. The objective of the present study was to establish an efficient technique of cloning miniature pigs by somatic cell nuclear transfer. A high pregnancy rate was achieved following transfer of parthenogenetic (3/3) and cloned (5/6) embryos using female miniature pigs in the early pregnancy period as recipients after estrus synchronization with prostaglandin F2 alpha analog and gonadotrophins. The production efficiency of the cloned miniature pigs using male and female fetal fibroblasts as nucleus donors was 0.9% (2/215 and 3/331, respectively). Cloned miniature pigs were also produced efficiently (7.8%, 5/64) by transferring reconstructed embryos into the uteri of common domestic pigs. When donor cells transfected with the green fluorescent protein (GFP) gene were used in nuclear transfer, the production efficiency of the reconstructed embryos and rate of blastocyst development were comparable to those obtained by non-transfected cells. When transfected cell-derived reconstructed embryos were transferred to three common domestic pig recipients, all became pregnant, and a total of ten transgenic cloned miniature pigs were obtained (piglet production efficiency: 2.7%, 10/365). Hence, we were able to establish a practical system for producing cloned and transgenic-cloned miniature pigs with a syngeneic background.

Developmental competence of somatic cell nuclear transfer embryos reconstructed from oocytes matured in vitro with follicle shells in miniature pig

The developmental competence of domestic pig oocytes that were transferred to somatic cell nuclei of miniature pig was examined. A co-culture system of oocytes with follicle shells was used for the maturation of domestic pig oocytes in vitro. Co-cultured oocytes progressed to the metaphase II stage of meiosis more quickly and more synchronously than non co-cultured oocytes. Oocytes were enucleated and fused with fibroblast cells of Potbelly miniature pig at 48 h of maturation. The blastocyst formation rate of nuclear transfer (NT) embryos using cocultured oocytes (24%) was significantly higher (p < 0.05) than that of non-co-cultured oocytes (13%). Cleaved embryos at 48 h after nuclear transfer using co-cultured oocytes were transferred to the oviducts of 14 Göttingen miniature pigs and four Meishan pigs. Estrus of all Göttingens returned at around 20-31 days of pregnancy. Two of the four Meishans became pregnant. Three and two cloned piglets were born after modest number of embryo transfer (15 and 29 embryos transferred), respectively. These results indicated that oocytes co-cultured with follicle shells have a high developmental competence after nuclear transfer and result in full-term development after embryo transfer.

Liquid storage of miniature boar semen

The effects of liquid storage at 15 degrees C on the fertilizing ability of miniature pig semen were investigated. Characterization of ejaculated semen from 3 miniature boars was carried out. Semen volume and pH were similar among these boars. In one of the boars, sperm motility was slightly low, and sperm concentration and total number of sperm were significantly lower than in the others (P < 0.01). Seminal plasma of the semen was substituted with various extenders (Kiev, Androhep, BTS and Modena) by centrifugation and semen was stored for 7 days at 15 degrees C. Sperm motility was estimated daily at 37 degrees C. For complete substitution of seminal plasma, Modena was significantly more efficient than the other extenders (P < 0.001) in retaining sperm motility. Semen from each of the 3 miniature boars that had been stored for 5 to 7 days at 15 degrees C in Modena was used for artificial insemination of 15 miniature sows. The farrowing rates were 100, 100 and 60%, and litter sizes were 6.4 +/- 1.5, 5.8 +/- 0.8 and 5.0 +/- 1.0 for each boar semen, respectively. The boar that sired the smallest farrowing rate was the same one that showed lower seminal quality with respect to sperm motility, sperm concentration and total number of sperm. These results suggest that miniature boar semen can be stored for at least 5 days at 15 degrees C by the substitution of seminal plasma with Modena extender.

Induction of superovulation and recovery of fertilized oocytes in prepubertal miniature pigs after treatment with PG600

The purpose of this study was to examine whether superovulation can be induced by hormonal treatment with PG600 (400 IU eCG and 200 IU hCG) at the prepubertal stage in miniature pigs. In Experiment 1, 14 prepubertal miniature pigs received 1, 1/2 or 1/4 vial of PG600, im on Day 0 (the first day of treatment). Presentation of estrus was monitored thereafter. On Days 10 to 13 (i.e., 6 to 8 d after estrus), the number of corpora lutea (CL) and residual follicles was counted by an exploratory laparotomy. Injection of 1/2 vial of PG600 effectively induced estrus and ovulation in the pigs. In Experiment 2, 15 prepubertal miniature pigs that received 1/2 vial of PG600 were artificially inseminated into the uterus by an exploratory laparotomy at 100 to 104 h after PG600 injection. Oocytes were recovered from the oviducts at 121 to 145 h after PG600 administration. The oocyte recovery rate was 66% (15 oocytes/pig, average), and 84% of these were at the 1-cell stage. In Experiment 3, 5 prepubertal miniature pigs that received 1/2 vial of PG600, followed by 100 IU hCG 70 h later, were artificially inseminated into the uterus. Oocytes were recovered synchronously at 120 to 122 h after PG600 treatment. The recovery rate was 80% (17 oocytes/pig, average) and 90% of the oocytes recovered were at the 1-cell stage. These results suggest that superovulation of prepubertal miniature pigs can be induced by 1/2 vial of PG600 injection, and by the combined treatment with PG600 and hCG injection, the fertilized ova can be synchronously recovered at around 120 h after PG600 injection. This procedure may provide a useful system for biomedical research using the miniature pigs, especially for producing transgenic animals for use in human disease models.