Sow litter size is increased in the subsequent parity when lactating sows are fed diets containing n-3 fatty acids from fish oil

Supplementing diets with n-3 fatty acids from fish oil has been shown to improve reproductive performance in dairy cattle and sheep, but there is little published literature on its effects in sows. The aim of this study was to evaluate the reproductive performance of sows fed fish oil as a source of n-3 PUFA prefarrowing and during lactation. From d 107.7 ± 0.1 of pregnancy, 328 sows ranging in parity from 0 to 7 (parity 1.95 ± 0.09, mean ± SE) were fed either a diet containing tallow (control) or an isocaloric diet containing 3 g of fish oil/kg of diet (n-3). Diets were formulated to contain the same amount of DE (13.9 MJ/kg), crude fat (54 g/kg), and CP (174 g/kg). Sows were fed their treatment diet at 3 kg daily for 8 d before farrowing and continued on treatment diets ad libitum until weaning at 18.7 ± 0.1 d of lactation. After weaning, all sows were fed a gestation diet without fish oil until their subsequent farrowing. There was no effect (P > 0.310) of feeding n-3 diets prefarrowing on piglet birth weight, preweaning growth rate, piglet weaning weight, or sow feed intake. However, n-3 sows had a larger subsequent litter size (10.7 ± 0.3 vs. 9.7 ± 0.3 total born; 10.2 ± 0.3 vs. 9.3 ± 0.3 born live; P < 0.05). In conclusion, this is the first study to demonstrate that feeding sows a diet containing n-3 PUFA from fish oil fed before farrowing and during lactation increased litter size in the subsequent parity independent of energy intake.

Piglets produced from in vivo blastocysts vitrified using the Cryologic Vitrification Method (solid surface vitrification) and a sealed storage container

The objective was to develop a simple successful porcine cryopreservation protocol that prevented contact between embryos and liquid nitrogen, avoiding potential contamination risks. In vivo-derived blastocysts were collected surgically from donor pigs, and two porcine embryo vitrification protocols (one used centrifugation to polarize intracytoplasmic lipids, whereas the other did not) were compared using the Cryologic Vitrification Method (CVM), which used solid surface vitrification. The CVM allowed embryos to be vitrified, without any contact between embryos and liquid nitrogen. Both protocols resulted in similar in vitro survival rates (90% and 94%) and cell number (89 ± 5 and 99 ± 5) after 48 h in vitro culture of vitrified and warmed blastocysts. The protocol that did not use centrifugation was selected for continued use. To protect vitrified embryos from contact with liquid nitrogen and potential contamination during storage, a sealed outer container was developed. Use of this sealed outer container did not affect in vitro survival of cryopreserved blastocysts. In vivo blastocysts (n = 151) were collected, vitrified, and stored using the selected protocol and sealed container. These embryos were subsequently warmed and transferred to six recipients; five became pregnant and farrowed a total of 26 piglets. This embryo vitrification method allowed porcine embryos to be successfully vitrified and stored without any contact with liquid nitrogen.

In vitro and in vivo characterization of putative porcine embryonic stem cells

We have developed a new method for the isolation of porcine embryonic stem cells (ESCs) from in vivo-derived and in vitro-produced embryos. Here we describe the isolation and characterization of several ESC lines established using this method. Cells from these lines were passaged up to 14 times, during which they were repeatedly cryopreserved. During this time, ESCs maintained their morphology and continued to express Oct 4, Nanog, and SSEA1. These cells formed embryoid bodies in suspension culture, and could be directed to differentiate into various lineages representative of all three germ layers in vitro. When injected into blastocysts these cells localized in the inner cell mass of blastocysts. To examine their pluripotency further, cells were injected into host blastocysts and transferred to recipient animals. Of the six transfers undertaken, one recipient became pregnant and gave birth to a litter of one male and three female piglets. Microsatellite analysis of DNA extracted from the tail tissue of these piglets indicated that two female piglets were chimaeric.

Maternal responses to daily maternal porcine somatotropin injections during early-mid pregnancy or early-late pregnancy in sows and gilts

Piglet neonatal survival and postnatal growth and efficiency are positively related to birth weight. In gilts, daily maternal porcine ST (pST) injections from d 25 to 100 (term approximately 115 d), but not d 25 to 50, of pregnancy increase progeny birth weight. Daily maternal pST injections from d 25 to 50 increase fetal weight at d 50 in gilts and sows. We therefore hypothesized that daily pST injections from d 25 to 100, but not d 25 to 50, of pregnancy would increase birth weight similarly in both parities. Landrace x Large White gilts and sows were uninjected (controls) or were injected daily with pST (gilts: 2.5 mg/d; sows: 4.0 mg/d, each approximately 15 microg of pST/kg per day) from d 25 to 50 or 100 of pregnancy. Litter size and BW were recorded at birth, midlactation, and weaning. Dams were followed through the subsequent mating and pregnancy. Maternal pST injections from d 25 to 100, but not d 25 to 50, increased mean piglet birth weight by 11.6% in sows (P <or= 0.001) and by 5.6% in gilts (P = 0.008). Both pST treatments decreased litter size by approximately 0.6 live-born piglets (each P <or= 0.025). In sows, maternal pST treatment from d 25 to 100 increased culls at weaning (P = 0.037). In remated dams, prior treatments did not affect (P > 0.1) the weaning-remating interval, conception rate, or subsequent litter size. Greater pST-induced birth weight increases in sows than in gilts may mean that underlying metabolic or placental mechanisms for pST action are constrained by maternal competition for nutrients in rapidly growing gilts.

Responses to maternal GH or ractopamine during early-mid pregnancy are similar in primiparous and multiparous pregnant pigs

Fetal growth is restricted in primiparous pigs (gilts) compared with dams who have had previous pregnancies (sows), as in other species. In gilts, daily maternal porcine GH (pGH) injections from day 25 to 50 of pregnancy (term approximately 115 day) increase fetal growth and progeny muscularity, and responses in sows are unknown. Whether feeding the beta(2)-adrenergic agonist ractopamine during this period increases progeny growth rates in either parity and fetal responses in gilts, have not been investigated. We hypothesised that fetal and placental growth and fetal muscle development would be increased more by maternal pGH and/or ractopamine during early-mid pregnancy in gilts than sows, since fetal growth is restricted in gilts causing lower birth weights. Large White x Landrace gilts and sows were injected daily with water (controls) or pGH (approximately 15 microg/kg per day), or were fed 20 ppm ractopamine, between day 25 and 50 of pregnancy. Maternal pGH increased litter average fetal weight (11%, P=0.007) and length (3%, P=0.022), but not placental weight, at day 50 of pregnancy, irrespective of parity, and had the greatest effects in the heaviest fetuses of each litter. Maternal ractopamine increased average fetal weight (9%, P=0.018), but not length. Muscle fiber diameter was increased by pGH in heavy littermates and by ractopamine in median littermates. Similar fetal growth responses to pGH and ractopamine in gilts and sows suggest that these hormones increase fetal nutrient availability similarly in both parities. We therefore predict that sustained pGH treatment will increase progeny birth weight, postnatal growth and survival, in both sows and gilts.

Effect of follicle size and dibutyryl cAMP on the cAMP content and gap junctional communication of porcine prepubertal cumulus-oocyte complexes during IVM

The lower ability of oocytes from prepubertal pigs to yield viable embryos than those from adult pigs appears, in part, a consequence of their reduced ability to accumulate cAMP during IVM. The present study examined the cAMP content of oocytes and cumulus-oocyte complexes (COCs), cumulus expansion and gap junctional communication (GJC) in COCs from 3- and 5-8-mm follicles during IVM. The effect of 1 mm dibutyryl cAMP (db-cAMP) treatment for the first 22 h of IVM was also examined for both follicle size classes. The cAMP concentration of oocytes from 5-8-mm follicles was threefold greater than that in oocytes from 3-mm follicles following 11 h of IVM (11.9 +/- 5.9 v. 3.6 +/- 1.8 fmol, respectively; P < 0.05). In the presence of db-cAMP, the cAMP content of oocytes from 3- and 5-8-mm follicles was no longer significantly different at 11 h IVM. The cAMP concentration of intact COCs from 5-8-mm follicles was significantly higher than that in COCs from 3-mm follicles at 11 h (1110.6 +/- 318.0 v. 116.9 +/- 55.7 fmol, respectively; P < 0.05). Despite maturation with db-cAMP, the cAMP content in COCs from 3- and 5-8-mm follicles at 11 h of IVM remained significantly different (15.1 +/- 4.9 v. 196.2 +/- 33.3 fmol, respectively; P < 0.05). The COCs from 3-mm follicles displayed lower cumulus expansion than did COCs from 5-8-mm follicles at both 11 h (cumulus expansion index (CEI) 1.0 +/- 0.1 v. 1.8 +/- 0.1, respectively; P < 0.01) and 22 h (CEI 1.9 +/- 0.3 v. 2.9 +/- 0.2, respectively; P < 0.05) of IVM. The level of cumulus cell-oocyte GJC decreased during IVM, with the number of GJC significantly greater in COCs from 3-mm compared with 5-8-mm follicles at both 6 h (613 +/- 55 v. 304 +/- 44 fluorescence intensity (FI), respectively; P < 0.05) and 11 h (644 +/- 99 v. 337 +/- 38 FI, respectively; P < 0.05) of IVM. By 22 h of IVM, the GJC of COCs from 3-mm follicles had decreased (227 +/- 18 FI) and was no longer significantly different to that of COCs from 5-8-mm follicles (139 +/- 15 FI; P > 0.05). Dibutyryl cAMP had no effect on the cAMP content, cumulus expansion or GJC of the whole COC. In conclusion, the results of the present study demonstrate that COCs from 3-mm follicles accumulate less intraoocyte and inter-COC cAMP, display lower cumulus expansion and maintain their cumulus cell-oocyte GJC for longer during IVM than do COCs from 5-8-mm follicles.

Adding essential amino acids at a low concentration improves the development of in vitro fertilized porcine embryos

The aims of this study were to investigate improvements to the pig preimplantation embryo culture system using in vitro produced embryos. For experiment 1, the optimum time to change the medium from NCSU23 containing 0.6 mM glucose, 0.2 mM pyruvate, 5.7 mM lactate and nonessential amino acids to NCSU23 containing 5.6 mM glucose and both essential and nonessential amino acids was examined. There were no statistically significant differences in blastocyst rates or cell number when the medium was changed at 48, 72 or 96 h, although there was a consistent trend for the 96 h treatment to produce fewer blastocysts with fewer cells. For experiment 2, the addition of essential amino acids at either a 1:50 or a 1:100 dilution of the purchased stock solution for day 1 to 6 or for days 3 to 6 only was investigated. Adding essential amino acids at a 1:50 dilution for day 3 to 6 significantly reduced the blastocyst rate and adding them at a 1:50 dilution from day 1 to 6 significantly reduced both the blastocyst rate and blastocyst cell number compared to when it was added at a 1:100 dilution. Embryos were produced by IVF, cultured for 6 days and good quality blastocysts were transferred into 6 synchronized pseudopregnant recipients (24 to 35 blastocysts per recipient) resulting in 4 pregnancies and 21 live birth piglets. These results show that adding essential amino acids at a 1:100 dilution provided the best culture conditions and the blastocysts produced were able to attain full term development after transfer.

Relationship between follicle size and oocyte developmental competence in prepubertal and adult pigs

The present study compared the distribution and steroid composition of 3-, 4- and 5-8-mm follicles on the surface of prepubertal and adult ovaries, and determined the relationship between follicle size and developmental competence of oocytes following parthenogenetic activation. The effect of 1 mm dibutyryl cAMP (dbcAMP) for the first 22 h of in vitro maturation (IVM) on the embryo development of prepubertal oocytes from the three follicle size cohorts was also determined. Compared with adult, prepubertal ovaries contained a higher proportion of 3-mm follicles (46 v. 72%, respectively), but a lower proportion of 4-mm (33 v. 22%, respectively) and 5-8-mm follicles (21 v. 6%, respectively). Adult follicular fluid (FF) contained 11-fold higher levels of progesterone (P4) than prepubertal FF, with similar levels observed between all adult follicle sizes. In prepubertal FF, the P4 concentration increased with follicle size from 3 to 4 to 5-8 mm. Rates of blastocyst development following parthenogenetic activation of adult oocytes from all three follicles sizes were similar (approximately 55%), whereas rates from prepubertal oocytes increased with increasing follicle size from 3 (17%) to 4 (36%) to 5-8 mm (55%). Treatment with dbcAMP for the first 22 h of IVM led to a 1.5-fold increase in the rate of blastocyst development for prepubertal oocytes from 3-mm follicles, but had no effect on prepubertal oocytes from the 4 and 5-8 mm classes. Mean blastocyst cell number increased with follicle size in prepubertal ovaries and was similar for all follicle sizes in adult ovaries. The present study demonstrates that the low efficiency of in vitro embryo production observed using prepubertal compared with adult pig oocytes is due to a greater proportion of 3-mm follicles on prepubertal ovaries, which contain oocytes of inferior developmental competence.

Production of homozygous alpha-1,3-galactosyltransferase knockout pigs by breeding and somatic cell nuclear transfer

We report here our experience regarding the production of double or homozygous Gal knockout (Gal KO) pigs by breeding and somatic cell nuclear transfer (SCNT). Large White x Landrace female heterozygous Gal KO founders produced using SCNT were mated with Hampshire or Duroc males to produce a F1 generation. F1 heterozygous pigs were then bred to half-sibs to produce a F2 generation which contained Gal KO pigs. To determine the viability of mating Gal KO pigs with each other, one female F2 Gal KO pig was bred to a half-sib and subsequently a full-sib Gal KO. F1 and F2 heterozygous females were also mated to F2 Gal KO males. All three types of matings produced Gal KO pigs. To produce Gal KO pigs by SCNT, heterozygous F1s were bred together and F2 fetuses were harvested to establish primary cultures of Gal KO fetal fibroblasts. Gal KO embryos were transferred to five recipients, one of which became pregnant and had a litter of four piglets. Together our results demonstrate that Gal KO pigs can be produced by breeding with each other and by SCNT using Gal KO fetal fibroblasts.

The Effect of Energy Substrate Concentration and Amino Acids on the In Vitro Development of Preimplantation Porcine Embryos

As the pig becomes increasingly used for biomedical research, an effective and efficient in vitro culture system is essential. This study aimed to improve the commonly used porcine embryo culture medium, NCSU23, by altering the energy substrates and adding amino acids, using electrically activated diploid parthenotes from oocytes obtained from the ovaries of prepubertal and adult animals. Morphological development to day 6 and blastocyst cell number were examined. Glucose (5.56 mM) was replaced by pyruvate and lactate (0.2 mM and 5.7 mM, respectively) for either the entire culture period or for the first 48 h only. Blastocyst rates were not different between any of the treatments, and were similar for prepubertal and adult oocytes. When the embryos were cultured with pyruvate and lactate for the first 48 h and then glucose, there was a significant increase in blastocyst cell number compared to glucose only. Blastocysts produced using pyruvate and lactate for the entire time tended to have more cells than those exposed to glucose only and less than those who were cultured in pyruvate and lactate for the first 48 h and then glucose. Nonessential amino acids added for the first 48 h and nonessential and essential amino acids added for the remaining time significantly increased blastocyst cell number only when the embryos were grown in pyruvate and lactate followed by glucose. Blastocyst rates were not different between any of the treatments, and this result was the same when using sow or gilt oocytes. The modified medium was then tested using in vitro matured and fertilized embryos from sow oocytes. Blastocyst rates and cell number were significantly increased in the modified medium compared to those grown in unmodified NCSU23. This shows that altering energy substrates and adding amino acids can increase the quantity and cell number of IVP blastocysts compared with NCSU23.

Use of adult mesenchymal stem cells isolated from bone marrow and blood for somatic cell nuclear transfer in pigs

Mesenchymal stem cells (MSCs) isolated from bone marrow were used to examine the hypothesis that a less differentiated cell type could increase adult somatic cell nuclear transfer (SCNT) efficiencies in the pig. SCNT embryos were produced using a fusion before activation protocol described previously and the rate at which these developed to the blastocyst stage compared with that using fibroblasts obtained from ear tissue from the same animal. The use of bone marrow MSCs did not increase cleavage rates compared with adult fibroblasts. However, the percentage of embryos that developed to the blastocyst stage was almost doubled, providing support for the hypothesis that a less differentiated cell can increase cloning efficiencies. As MSCs are relatively difficult to isolate from the bone marrow of live animals, a second experiment was undertaken to determine whether MSCs could be isolated from the peripheral circulation and used for SCNT. Blood MSCs were successfully isolated from four of the five pigs sampled. These cells had a similar differentiation capacity and marker profile to those isolated from bone marrow but did not result in increased rates of development. This is the first study to our knowledge, to report that MSCs can be derived from peripheral blood and used for SCNT for any species. These cells can be readily obtained under relatively sterile conditions compared with adult fibroblasts and as such, may provide an alternative cell type for cloning live animals.

Effect of dibutyryl cAMP on the cAMP content, meiotic progression, and developmental potential of in vitro matured pre-pubertal and adult pig oocytes

Pre-pubertal pig oocytes display reduced developmental competence compared with adult oocytes following in vitro maturation (IVM). Exposure to dibutyryl cyclic adenosine monophosphate (dbcAMP) for the first 20 hr IVM improves development of pre-pubertal oocytes, suggesting that their cAMP content may be inadequate. This study examined the effect of 1 mM dbcAMP treatment for the first 22 hr of IVM on the cAMP content, meiotic progression, and embryo development of pre-pubertal and adult oocytes. In control groups, a two-fold increase in cAMP was observed in adult oocytes after 22 hr IVM, with no change in pre-pubertal oocyte cAMP content. At 22 hr IVM, dbcAMP treatment resulted in two- and five-fold increases in pre-pubertal and adult oocyte cAMP, respectively. After 22 hr control IVM, a greater proportion of pre-pubertal oocytes occupied metaphase I (MI) compared with adult oocytes (69% vs. 49%). dbcAMP treatment reduced the proportion of pre-pubertal and adult oocytes in MI stage at 22 hr. Despite dbcAMP treatment, the proportion of pre-pubertal oocytes in the MI stage at 22 hr remained higher than that of adult oocytes. In control groups, adult oocytes displayed a greater ability to form blastocysts compared with pre-pubertal oocytes following either parthenogenetic activation (59% vs. 25%) or in vitro fertilization (IVF) (47% vs. 19%). dbcAMP treatment increased subsequent blastocyst formation rates of pre-pubertal oocytes, whereas blastocyst formation rates of adult oocytes remained unchanged. Our results suggest that the reduced developmental capacity of pre-pubertal oocytes may be a consequence of their reduced ability to accumulate cAMP during IVM.

Relationship between donor animal age, follicular fluid steroid content and oocyte developmental competence in the pig

The developmental competence of oocytes recovered from the ovaries of slaughtered prepubertal and adult pigs was evaluated after in vitro maturation, parthenogenetic activation and culture in vitro. In addition, the effect of prepubertal and adult follicular fluid (FF) on the developmental competence of prepubertal and adult oocytes was investigated. When matured in adult FF, the rates of cleavage (92 v. 73% P < 0.01) and blastocyst formation (57 v. 38%; P < 0.05) were greater for adult oocytes than for prepubertal oocytes. Blastocysts derived from adult oocytes had more trophectoderm cells (43 v. 30; P < 0.05) and total cells (51 v. 36; P < 0.05) than blastocysts derived from prepubertal oocytes. The developmental competence of prepubertal oocytes was not affected by the FF donor age, whereas the developmental competence of adult oocytes was. Blastocysts derived from adult oocytes matured in adult FF had more trophectoderm cells (38 v. 24; P < 0.005), inner cell mass cells (7 v. 3; P < 0.01) and total cells (45 v. 27; P < 0.001) than blastocysts derived from adult oocytes matured in prepubertal FF. Characterization of the steroid content of the FF used to supplement the maturation medium revealed that adult FF contained more progesterone (42 v. 23 ng mL(-1); P < 0.005) and androstenedione (70 v. 16 ng mL(-1); P < 0.05) than prepubertal FF. In addition, the molar ratios of progesterone to androstenedione, androstenedione to 17beta-oestradiol and androstenedione to testosterone differed (P < 0.05) between prepubertal and adult FF. The results support the hypothesis that a greater proportion of adult oocytes than of prepubertal oocytes has completed 'oocyte capacitation'. The differences in FF steroid content are indicative of the different follicular environments from which the prepubertal and adult oocytes were isolated, and may be attributed to the observed effects on oocyte developmental competence.

Sex differentiation and germ cell production in chimeric pigs produced by inner cell mass injection into blastocysts

This study aimed at collecting background knowledge for chimeric pig production. We analyzed the genetic sex of the chimeric pigs in relation to phenotypic sex as well as to functional germ cell formation. Chimeric pigs were produced by injecting Day 6 or Day 7 inner cell mass (ICM) cells into Day 6 blastocysts. Approximately 20% of the piglets born from the injected blastocysts showed overt coat color chimerism regardless of the embryonic stage of donor cells. The male:female sex ratio was 7:2 and 6:1 in the chimeras derived from Day 6 and Day 7 ICM cells, respectively, showing an obvious bias toward males. When XX donor cells were injected into XY blastocysts at the same embryonic stage, the phenotypic sex of the resulting chimera was male with no germ-line cells formed from the donor cell lineage. On the other hand, when the donor was XY and the recipient blastocyst was XX, the phenotypic sex of the chimera was male, and germ-line cells were derived only from the donor cells. The combination of XY donor cells and XY blastocysts produced some chimeras in which the donor cell lineage did not contribute to germ-line formation even when it appeared in coat color. When the embryonic stage of the donor was advanced by 1 day in the XY-XY combination, 100% of the germ-line cells of the chimeras were derived from the donor cell lineage. These data showed that characteristics of sex differentiation and germ cell formation in chimeric pigs are similar to those in chimeric mice.

Targeting gene expression to endothelium in transgenic animals: a comparison of the human ICAM-2, PECAM-1 and endoglin promoters

It is highly likely that successful pig-to-human xenotransplantation of vascularized organs will require genetic modification of the donor pig, and in particular of donor vascular endothelium. Promoters are generally tested in transgenic mice before generating transgenic pigs. Several promoters have been used to drive endothelial cell-specific expression in mice but none have yet been tested in pigs. We compared the promoters of three human genes that are predominantly expressed in vascular endothelium: intercellular adhesion molecule 2 (ICAM-2), platelet endothelial cell adhesion molecule 1 (PECAM-1) and endoglin. Expression of human complement regulatory proteins (hCRPs), directed by each of the promoters in mice, was largely restricted to vascular endothelium and leukocyte subpopulations. However, expression from the PECAM-1 promoter was weak in liver and non-uniform in the small vessels of heart, kidney, and lung. Conversely, expression from the endoglin promoter was consistently strong in the small vessels of these organs but was absent in larger vessels. The ICAM-2 promoter, which produced strong and uniform endothelial expression in all organs examined, was therefore used to generate hCRP transgenic pigs. Leukocytes from 57 pigs containing at least one intact transgene were tested for transgene expression by flow cytometry. Forty-seven of these transgenic pigs were further analyzed by immunohistochemical staining of liver biopsies, and 18 by staining of heart and kidney sections. Only two of the pigs showed expression, which appeared to be restricted to vascular endothelium in heart and kidney but was markedly weaker than in transgenic mice produced with the same batch of DNA. Thus, in this case, promoter performance in mice and pigs was not equivalent. The weak expression driven by the human ICAM-2 promoter in pigs relative to mice suggests the need for additional regulatory elements to achieve species-specific gene expression in pigs.

Effect of 6-dimethylaminopurine on electrically activated in vitro matured porcine oocytes

The effect of the protein kinase inhibitor, 6-dimethylaminopurine (6-DMAP), on the maturation promoting factor (MPF) activity, pronuclear formation, and parthenogenetic development of electrically activated in vitro matured (IVM) porcine oocytes was investigated. Oocytes were activated by exposure to two DC pulses, each of 1.5 kV/cm field strength and 60 microsec duration, applied 1 sec apart. In the first experiment, subsequent incubation with 2 or 5 mM 6-DMAP for 3 hr increased the incidence of blastocyst formation compared with no treatment, whereas incubation with 2 or 5 mM 6-DMAP for 5 hr did not. In the proceeding experiments, oocytes exposed to 6-DMAP were incubated with 2 mM of the reagent for 3 hr. Assaying histone H1 kinase activity in the second experiment revealed that the levels of active MPF in electrically activated oocytes treated with 6-DMAP were depleted more rapidly and remained depleted for longer compared with electrical activation alone. The kinetics of MPF activity following 6-DMAP treatment were similar to that found in inseminated oocytes in the third experiment. The effect of 6-DMAP was correlated with an increased incidence of parthenogenetic blastocyst formation. A fourth experiment was undertaken to examine the diploidizing effect of 6-DMAP. Electrically activated oocytes treated with 6-DMAP and cytochalasin B, either alone or in combination, displayed a higher incidence of second polar body retention compared with those that were untreated or treated with cycloheximide alone. After 6 days of culture in vitro, parthenotes exposed to 6-DMAP, either alone or in combination with cytochalasin B, formed blastocysts at a greater rate compared with those exposed to cytochalasin B alone, cycloheximide alone or no treatment. The combined 6-DMAP and cytochalasin B treatment induced the highest rate of blastocyst formation (47%), but the numbers of trophectoderm and total cells in these blastocysts were lower compared with those obtained following exposure to 6-DMAP alone. These results suggest that the increased developmental potential of 6-DMAP-treated parthenotes may be attributable to the MPF-inactivating effect of 6-DMAP, rather than the diploidizing effect of 6-DMAP.

Piglets born from centrifuged and vitrified early and peri-hatching blastocysts

Cryopreservation of zona-intact porcine embryos has been relatively unsuccessful to date, although some success has been obtained with lipid reduced morulae and early blastocysts. This study adapted some vitrification protocols used successfully with late blastocysts for use with early zona-intact blastocysts, using actin depolymerization, centrifugation, and open-pulled (OPS) straws. Initially, Day 6 peri-hatching blastocysts were collected, cultured for 40 min in 7.5 microg/ml cytochalasin B and vitrified in 6.5 M glycerol and 6% BSA (VS1) in either heat-sealed (HS) or open straws (OS). The post-thaw survival of those stored in HS was 15.4% after 24 and 48 h in vitro; storage in OS significantly improved survival (58.8% for both 24 and 48 h). When similar stage blastocysts were cultured in cytochalasin B and vitrified with 8 M ethylene glycol and 7% polyvinylpyrrolidone (PVP; VS2) in OS, survival was 44.4 and 33.3% for 24 and 48 h, respectively. Day 5 late morulae and early blastocysts were collected, cultured with cytochalasin B, and centrifuged or left intact (control), then vitrified with VS1 in HS or OS, or vitrified in VS2 in OS only. None of the intact control embryos survived thawing and 48 h culture in vitro. Centrifuged early blastocysts vitrified with VS1 showed good post-thaw survival in culture when stored in HS (62.8 and 60.5% for 24 and 48 h, respectively), or OS (75 and 63.6%). When vitrified with VS2 in OS, survival improved (80 and 76.7%). Peri-hatching blastocysts were vitrified in VS1, and early blastocysts were vitrified with VS1 and VS2. All blastocysts were stored in OS. The embryos were recovered and transferred to Day 4 and 5 pseudopregnant recipients (for Day 5 and 6 blastocysts, respectively). Of the five recipients receiving peri-hatching blastocysts, two became pregnant and delivered a total of eight piglets. All three recipients of early blastocysts vitrified in VS1 had a delayed return to estrus; while of the four receiving embryos vitrified with VS2, two were delayed in returning to estrus, and one was confirmed pregnant after 45 days. A litter of five piglets, one male and four female, was produced at 116 days of gestation. To our knowledge, this is the first litter of piglets produced from early blastocysts vitrified without micromanipulation to remove polarized lipid droplets.

Production of cloned pigs from cultured fetal fibroblast cells

Somatic cell nuclear transfer was used to produce live piglets from cultured fetal fibroblast cells. This was achieved by exposing donor cell nuclei to oocyte cytoplasm for approximately 3 h before activation by chemical means. Initially, an experiment was performed to optimize a cell fusion system that prevented concurrent activation in the majority of recipient cytoplasts. Cultured fibroblast cells were fused in medium with or without calcium into enucleated oocytes flushed from superovulated gilts. Cybrids fused in the presence of calcium cleaved at a significantly (P < 0.05) greater rate (69%, 37 out of 54) after 2 days of culture compared with those fused without calcium (10%, 7 out of 73), suggesting that calcium-free conditions are needed to avoid activation in the majority of recipient cytoplasts during fusion. In the second experiment, cybrids fused in calcium-free medium were activated approximately 3 h later with ionomycin, followed by incubation in 6-dimethylaminopurine to determine development in vitro. Following 2 days of culture, cleavage rates of chemically activated and unactivated cybrids (fusion without activation control) were 93% (100 out of 108) and 7% (2 out of 27), respectively. After an additional 5 days of culture, activated cloned embryos formed blastocysts at a rate of 23% (25 out of 108) with an average inner cell mass and trophectoderm cell number of 10 (range, 3 to 38) and 31 (range, 16 to 58), respectively. In the third experiment, activated nuclear transfer embryos were transferred to the uteri of synchronized recipients after 3 days of culture to assess their development in vivo. Of 10 recipients receiving an average of 80 cleaved embryos (range, 40 to 107), 5 became pregnant (50%) as determined by ultrasound between Day 25 and Day 35 of gestation. Of the five pregnant recipients, two subsequently farrowed one piglet per litter originating from two different cell culture lines. In this study, efficient reprogramming of porcine donor nuclei by fusing cells in the absence of calcium followed by chemical activation of recipient cytoplasts was reflected in high rates of development to blastocyst and pregnancy initiation leading to full term development.

Efficient generation of alpha(1,3) galactosyltransferase knockout porcine fetal fibroblasts for nuclear transfer

Pigs are currently considered the most likely source of organs for human xenotransplantation because of anatomical and physiological similarities to humans, and the relative ease with which they can be bred in large numbers. A severe form of rejection known as hyperacute rejection has been the major barrier to the use of xenografts. Generating transgenic pigs for organ transplantation is likely to involve precise genetic manipulation to ablate the alpha(1,3) galactosyltransferase (galT) gene. In contrast to the mouse, homologous recombination in livestock species to ablate genes is hampered by the inability to isolate functional embryonic stem cells. However, nuclear transfer using genetically targeted cultured somatic cells provides an alternative means to producing pigs deficient for galT. In this study we successfully produced galT+/- somatic porcine fetal fibroblasts using two approaches; positive negative selection (PNS) using an isogenic targeting construct, and with a promoterless vector using non-isogenic DNA.

Effect of DNA concentration on transgenesis rates in mice and pigs

A retrospective analysis of transgenesis rates obtained in seven pronuclear microinjection programs was undertaken to determine if a relationship existed between the amount of DNA injected and transgenesis rates in the pig. Logistic regression analysis showed that as the concentration of DNA injected increased from 1 to 10 ng/microl, the number of transgenics when expressed as a proportion of the number liveborn (integration rate) increased from 4% to an average of 26%. A similar relationship was found when the number of molecules of DNA injected per picolitre was analysed. No evidence was obtained to suggest either parameter influenced integration rate in mice when the same constructs were injected. The number of transgenics liveborn when expressed as a proportion of ova injected (efficiency rate), increased as DNA concentration increased up to 7.5 ng/microl and then decreased at 10 ng/microl for both species suggesting that at this concentration DNA (or possible contaminants) may have influenced embryo survival. The relationship between efficiency and the number of molecules injected per picolitre was complex suggesting that the concentration at which DNA was injected was a better determinant of integration and efficiency rates. In conclusion, the present study suggests that transgenes need to be injected at concentrations of between 5 and 10 ng/microl to maximise integration and efficiency rates in pigs.

Activation of in vivo- and in vitro-derived porcine oocytes by using multiple electrical pulses

The current protocols used to activate pig nuclear transfer embryos are less efficient than those used for other species. To address this problem, the effect of multiple sets of electrical pulses on the parthenogenetic development of in vivo- and in vitro-derived porcine oocytes was examined. Each set of pulses consisted of two 1.5 kV cm(-1) DC pulses of 60 micros duration each, administered 1 s apart. For in vivo-derived oocytes, application of a second set of pulses 30 min after the first set increased the proportion of oocytes that developed to the blastocyst stage compared with a single treatment (51 v. 34%). Application of a third set of pulses 30 min after the second set reduced the rate of blastocyst formation compared with two sets of pulses. In contrast, the rate of blastocyst formation was greater with one set of pulses compared with two sets for in vitro matured oocytes (31 v. 16%). Additional sets of electrical pulses did not affect the number of cells in blastocysts obtained from either group of oocytes compared with a single treatment. In summary, the study demonstrates that the application of a second set of activating pulses 30 min after the first set is beneficial to in vivo-derived oocytes, but detrimental to in vitro matured oocytes, in terms of their ability to develop parthenogenetically to the blastocyst stage.