The extent of embryo mortality is usually estimated by the difference between the numbers of corpora lutea and embryos in the same animal, which assumes that each corpora lutea represents one potential embryo. Recent observations from the authors' laboratory reveal situations in which the number of embryos exceeds the number of corpora lutea, implicating the presence of identical twins. The objective of the present study was to establish DNA fingerprinting techniques to investigate the prevalence of monozygotic twinning in two breeds of pig. DNA fingerprints of every fetus carried by 6 Meishan (MS) and 6 Landrace x Large White (LxLW) gilts on Day 29 +/- 2 of pregnancy were obtained. Five LxLW and 3 MS litters carried no identical fetuses. The remaining gilts carried a pair of fetuses with indistinguishable DNA profiles. No pairs of fetuses were monochorionic. These results suggest that monozygotic twinning in the pig occurs during embryo cleavage or blastocyst development and may be more prevalent in MS compared with indigenous breeds.
- embryo survival
- conceptus growth