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57 developmental characteristics of later-stage porcine embryos produced in vivo or in vitro

Callesen, H., Holm, P.
Reproduction, fertility, and development 2016 v.28 no.2 pp. 158-159
blastocyst, cell cycle, cell viability, early development, embryogenesis, hatching, in vitro culture, in vitro studies, insemination, morula, oocytes, sows, zona pellucida, zygote
Kinetics and morphological characteristics during pre-implantation embryo development are well established in most mammals. In porcine, such studies are few because of limited use of in vitro culture, but this has changed in recent years due to increasing use of in vitro production and cloning. Therefore, additional characterisation of especially later stage porcine embryos is needed. Here we studied in vitro development of porcine in vivo- and in vitro-derived zygotes collected from weaned, inseminated sows (slaughtered 2 days after first insemination; in vivo group, n=112) or produced from immature oocytes from sow ovaries (matured and fertilized: Theriogenology 63, 2040–2052; in vitro group, n=210). Both types were cultured for 7 days in vitro (Theriogenology 63, 2040–2052) in a time-lapse system (Theriogenology 50, 1285–1299) with images recorded every 0.5h. Individual embryos were followed and characterised for stage and quality from first cleavage. The following was recorded: (i) zygote: inner (i.e. ooplasma) and outer diameter [i.e. including zona pellucida (ZP)], ZP thickness; (ii) compact morula: areas of compacted inner cells and of cellular debris; (iii) blastocyst: partial or total collapse of blastocoelic cavity and diameter at maximal expansion immediately before hatching. At the 1-cell stage, no difference was found between in vivo v. in vitro zygotes in ZP diameter (approximately 150µm) and thickness (approximately 15.6µm). In both groups, cleavage rate was around 65%, but more in vivo (85%) than in vitro (28%) zygotes developed beyond the morula stage. Embryos of both types that did not develop to this stage (n=212) blocked predominantly at the 1st (50%) or 2nd (21%) cell cycle. Cell cycles were generally shorter in in vivo v. in vitro zygotes from compact morula until the hatched blastocyst stage (mean 128 v. 139h from the 2-cell stage for in vivo v. in vitro; P<0.05). Compacted in vivo morulae were 25% larger than in vitro, and the debris area was more than twice as large in in vitro. Hatching occurred after approximately two collapses in both in vivo and in vitro but at a larger ZP diameter in vitro. See Table 1 for further details. This study illustrates differences and similarities between morphology and developmental kinetics of in vivo- and in vitro-derived porcine zygotes, but also how various morphological characteristics indicate some of the possible causes of the reduced developmental ability of in vitro embryos. The in vitro period seems to result in more stressful conditions for the embryos, both during early development, but also during the later stages leading to the hatching process. Thus, further optimization of in vitro culture conditions is still needed in porcine. Table 1.Compact morula (CM) viable cell mass and debris, hatched blastocyst (HB) diameter, and early-hatched blastocyst (EB-XB) and expanded-hatched blastocyst (XB-HB) collapses for in vivo- and in vitro-derived zygotes.