Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: January 17, 1998
Publication Date: N/A
The freemartin syndrome is a distinct form of intersexuality resulting from in utero masculinization of the female fetus by its co-twin male; 96.7% of the females are sterile. Internal genitalia of the freemartin exhibit gross anatomical anomalies indicative of partial or total inhibition of the female reproductive system during embryonic development (gonadal hypoplasia, repression of Mullerian duct derivatives -- absence of uterine body, cervix and anterior vagina) and masculinization of the Wolffian duct system. Fusion of the placental chorion and anastomosis of chorioallantoic arterial blood vessels between adjacent fetuses allows exchange of hemopoietic stem cells and germ cells (XX/XY chimerism) and of hormones controlling development of the male's reproductive system (e.g., androgens and anti-Mullerian hormone). Chorioallantoic anastomosis in cattle occurs between Day 30 and 50 of gestation and just prior to sexual development, which begins earlier in male than females fetuses. The male testis is recognizable on Day 39 or 40 of gestation compared to Day 47 to 49 for the female gonad. Production of anti-Mullerian hormone begins about Day 40 and its mediation of physiological regression of Mullerian ducts in both male and freemartin fetuses occurs between Day 50 and 80. If the testis-determi genes is absent on the Y chromosome, the fetal male gonad becomes an ovary. Unlike the freemartin, the chimeric co-twin bull is generally phenotypically normal and has normal fertility. Economic value of infertile freemartins is in meat production. Freemartin carcasses are 10-15% lighter (P<.01) and yield 2-3% less (P<.01) retail product than the co-twin steer. Conversely, increased intramuscular fat (marbling) results in 90% of the carcasses with a USDA grade of choice or prime.