60,XX/60,XY chimerism and freemartinism in heterosexual bovine twins

Abstract

In this study, 42 heterosexual bovine twins (10 co-borned couples, 19 females, and three males) were cytogenetically evaluated. These animals from several bovine breeds, mainly Holstein (17) and Brown Swiss (11), were herded in particular farms located in different regions of the State of São Paulo and from the Institute of Animal Science and Pastures (IZ), Nova Odessa, SP. Cytogenetic analysis were assessed in metaphases from cultured lymphocytes. The 60,XX/ 60XY chimerism were observed 90.5% of the animals and it varied from 1.8 to 90.2% of female cells. From all chimeric animals 3,806 cells were evaluated, among them 1,268 were XX cells (33.3%) and 2,538 were XY cells (66.7%). In nine co-borned couples, female cell rates ranged from 24.8 to 21.5% and male cell rates from 75.2 and 78.5% in males and females, respectively. In one couple, there was no evidence of cell exchange between twins with female presenting only female cells and male only male cells. Three adult females were slaughtered and evaluated. Their reproductive tracts presented several degrees of masculinization, including clitoris enlargement, vagina, cervix, uterus and uterine tube subdevelopment, presence of vesicular gland and gonads ovotestis. One of these three females presented cervix absence. Among the 29 evaluated female, three presented the 60,XX karyotype. Two of them were normal females who delivery at 30 months old, while the other still have not achieved reproductive age, but it seems to have normal reproductive function. From 13 analyzed males, 12 presented 60,XX/60/XY chimerism and one presented normal katyotype (60,XY). Cytogenetic analysis is an efficient and a less expensive method to early diagnosis of freemartinism in bovine females born co-twin with males, which allows the chimeric animal to be eliminated from the reproductive process, decreasing management costs and reducing rates of such anomaly in commercial breedings.