Chimeric cattle are not at all rare. When a cow has twins, it is almost inevitable that anastomoses (areas of joining) develop between the fetal circulatory systems early in gestation. This leads to exchange of blood between the two fetuses. Fetal blood contains hematopoietic stem cells, and each fetus is permanently "seeded" with stem cells from its twin. The result is that both animals are hematopoietic chimeras. A variable fraction of all their cells that are derived from hematopoietic stem cells (peripheral blood cells, Kupffer cells in the liver, lymphocytes and macrophages in lymph nodes and spleen, etc) are from the twin.
Major clinical signifcance is seen when one fetus is a female and one a male. In such cases, the female fetus is exposed to hormones from the male and is masculinized. Such female cattle are called freemartins. The external genital tract of a freemartin looks like a female, although usually infantile. The degree to which the internal genital tract is masculinized varies, but typically, the vagina is very short and uterine horns are rudimentary. Pretty obviously, these animals are sterile. Freemartins are seen occasionally in other species, although much less commonly than in cattle, probably because those animals do not have the propensity seen in cattle to form vascular anastomoses among fetuses early in gestation.
that would be interesting, but i doubt they are fetilized. Nice fish BTW, very beautiful.
