Blood types of twin cattle after embryo transfer to inseminated recipients

The blood types, together with erythrocyte and plasma protein types were determined in 10 pairs of twins born after embryo transfer to the contralateral uterine horns of previously inseminated recipients. These estimations were carried out at the age of nine weeks. According to the haemolytic test, most of these pairs of twins had identical blood types, ie, no erythrocyte mosaic could be demonstrated and the blood type corresponded to that of the recipient's calf. In the cases where mosaicism could be demonstrated, the recipient calf's blood type predominated. The reason for this bias remains unclear although the suggestion that the recipient's calf had developed further and was thus able to influence the haematopoietic tissues of its co-twin is worth considering.