The impact of either a Meishan or Yorkshire uterus on Meishan or Yorkshire fetal and placental development to days 70, 90, and 110 of gestation.

Abstract

Straightbred Yorkshire (Y) conceptuses are larger than straightbred Meishan (M) conceptuses throughout gestation and at farrowing. In contrast, when Y and M conceptuses were gestated together in Y recipient females, the birth weight of M pigs was similar to that of their Y littermates. Even though placentae of M pigs remained markedly smaller than placentae of Y littermates, they were significantly more vascular. The objective of this study was to compare and contrast the changes in Y and M conceptus growth and placental-endometrial vascularity throughout late gestation in Y or M uteri. Gravid uteri were recovered at slaughter from M and Y females that were gestating either M or Y conceptuses on d 70, 90, or 110 of gestation. Uterine and conceptus measurements were recorded, and a section of the intact endometrial-placental attachment site for each conceptus was fixed, embedded, and later evaluated for placental and endometrial vascular density. Placental surface area and weight were greater (P < .001) when M or Y conceptuses were recovered from Y uteri compared with M uteri on each day of gestation examined. Further, by d 110, the surface area of Y placentae was greater (P < .001) than that of M placentae, regardless of uterine type in which they were gestated. The vascular density of M placentae and adjacent endometrium doubled (P < .05) between d 70 and 110 of gestation (3.0 and 2.5 vs 6.0 and 5.1%, respectively), with no significant increase in placental surface area. In contrast, the surface area of Y placentae doubled in size (P < .001) between d 90 and 110 of gestation, but placental and adjacent endometrial vascular density remained relatively constant, averaging 3.2 and 3.8%, respectively. These data are consistent with the premise that placental size is largely determined by the uterus in which a conceptus is gestated until approximately d 90. After d 90, fetal breed-specific mechanisms maintain optimal fetal growth. Between d 90 and term, M fetal growth depends on progressive increases in placental blood vessel density and requires no increase in placental size. In contrast, Y conceptuses seem to rely exclusively on placental growth to increase placental-endometrial surface area for nutrient exchange.

Number of conceptuses in utero affects porcine fetal muscle development

“…If the placental compensatory mechanisms described by Biensen et al (1998) are not adequate, crowding may still affect fetal development. This raises important questions for both fetal and postnatal development, particularly with respect to the development of fetal muscle fibres, which start to differentiate around day 35 of gestation in the pig (Wigmore & Stickland 1983).…”

Production of Transgenic Cloned Miniature-Pigs with Membrane-Bound Human Fas Ligand (FasL) by Somatic Cell Nuclear Transfer.

“…33 Here, we hypothesize that breed differences between cell donors and recipients is an important factor affecting the success of cloning of miniature pigs. …”

Estudio de los factores materno-embrionario que determinan la fertilidad y prolificidad en una línea de conejo seleccionada por velocidad de crecimiento

“…Los estudios de transferencias recíprocas se han utilizado en diversas especies de mamíferos, como en ratón (Al-Murrani y Roberts, 1978;Bradford, 1979;Pomp et al, 1989), cerdo (Ashworth et al, 1990; Youngs et al, 1994;Biensen et al, 1998) o conejo , con el fin de conocer los efectos materno y embrionario en la supervivencia embrionaria, con resultados controvertidos. En este trabajo se han realizado transferencias recíprocas aprovechando la independencia de los cuernos uterinos en conejo de modo que la hembra receptora siempre recibía embriones pertenecientes a su línea en uno de sus oviductos y el mismo número de embriones de la otra línea en el oviducto opuesto.…”

“…Resultados similares ya han sido publicados por otros autores en otras especies como cerdo (Ashworth et al, 1990;Biensen et al, 1998;Wilson et al, 1998) o ratón (Hetherington, 1971;Al-Murrani y Roberts, 1978). Sin embargo, otros autores observaron mayor importancia del genotipo materno en otras líneas de conejo, seleccionadas por diferentes criterios .…”

“…Aunque en general, los resultados no son concluyentes, algunos autores en estudios en ratón (Bradford, 1979;Pomp et al, 1989) y en vacuno (Klindt y Maurer, 1986) concluyen que la supervivencia embrionaria y el crecimiento prenatal dependen, en gran medida, del genotipo materno. No obstante, otros autores indican que el genotipo embrionario y, sobre todo, la interacción entre ambos genotipos también influye en la supervivencia embrionaria, el crecimiento embrionario y placentario en ratón (Hetherington, 1971; Al-Murrani y Roberts, 1978), cerdo (Ashworth et al, 1990;Biensen et al, 1998;Wilson et al, 1998) y conejo (Mocé et al, 2004.y ratones (ErnstLos criterios de selección en conejo suelen ser el tamaño de camada y la velocidad de crecimiento (ganacia de peso diaria durante el cebo) con el fin de aprovechar la complementariedad de estos caracteres en el sistema de producción. La relación genética entre ambos se ha abordado mediante la estimación de parámetros genéticos o bien, de las respuestas correlacionadas a la selección por tamaño de camada .…”