FREEMARTINISM AMONG SINGLETON BOVINE FEMALES BORN FROM MULTIPLE EMBRYO-TRANSFER

Heterosexual chimerism among singleton females produced by multiple no nsexed embryo transfer (MNET singleton females) was investigated using chromosome typing and PCR (polymerase chain reaction)-amplification o f male-specific DNA (msDNA). Of the 22 animals tested, 21 were classif ied as normal by both methods (i.e., showing no male cells among 100 m etaphase spreads in chromosome typing and being msDNA negative in PCR) . No morphological abnormalities of the genital organs were observed a mong 19 MNET single females. One MNET singleton female was, however,cl assified as a freemartin by PCR (male-specific DNA positive), but it w as classified as normal cytogenetically. This individual probably had a low degree of heterosexual chimerism, and it seems that the chimeris m derived from MNET was difficult to diagnose by chromosome typing, al though it was detectable by PCR. The genital organs of this individual (15-mo-old Aberdeen Angus) were normal in form (both external and int ernal) and size. However, a very small structure, resembling seminifer ous tubule, was found in the left ovary. It may be concluded that most MNET singleton females are expected to have normal reproductive funct ion.