Non-Freemartin Rate in Holstein Heterosexual Twins

Abstract

Bovine freemartinism is the sexual modification of a female twin by in utero exchange of blood from a male fetus. This condition was first described by Hunter in 1779¹ and was well known to result in sterility. The freemartin syndrome occurs in around 92% of bovine females born as a result of heterosexual twin pregnancies², which indicates 8% of female heterosexual twins will be normal. The diagnosis of freemartinism can be established by one of the following methods: 1) clinical genital abnormalities; 2) presence of sex chromatin bodies in circulating leukocytes in male co-twin; 3) presence of sex chromosome chimerism (XX/XY) of hemopoietic cells; 4) blood typing; and 5) skin grafting. In order to promote the preservation of ideal genetic traits in newborn heterosexual co-twin heifer calves in the Holstein breed, the American Holstein Association authorized our laboratory to cytogenetically test calves for potential freemartinism. The purpose of this paper is to review the cytogenetical results of testing Holstein heifer heterosexual twins referred to our laboratory in the last 13 years.