Test Detail

Freemartinism is the intersexuality characteristic of the female calf that is a twin of a male, produced by fusion of the placental membranes during gestation. The blood exchange between the fetuses generates XX/XY chromosomal chimerism and partial masculinisation of the female reproductive tract. The practical consequence is infertility in most of these females. The test detects Y-chromosome DNA in the female's blood, confirming the chimerism quickly and reliably.

The frequency depends on that of twin births, more common in high-production dairy cattle than in beef breeds. It is not associated with a specific breed. Of mixed-sex twin births, the vast majority of females are freemartins.

- Infertility in the vast majority of female twins of a male
- Absent or irregular oestrous cycles
- Shortened vagina, appreciable on examination
- Hypoplastic or ambiguous internal genitalia
- Occasional masculinised behaviour
- Larger size and 'male' conformation in some cases

The phenomenon has been known since antiquity and farmers exploited it empirically to cull sterile cows long before its cause was understood. In 1916, Frank R. Lillie formulated the correct theory: vascular anastomosis of the twin placentas masculinises the female through the action of the male's hormones and cells. In the 1960s, karyotype studies demonstrated XX/XY chromosomal chimerism in freemartins. Subsequently, Y-chromosome DNA detection by PCR replaced karyotyping as the routine method, owing to its speed and lower cost.

- Test every female born with a male twin, or from a twin gestation of unknown sex, before including her in replacement stock
- Confirm XX/XY chimerism by Y-chromosome DNA detection in blood
- Confirmed freemartin: remove her from breeding and send her for fattening
- It is not hereditary: it does not penalise parents or siblings in genetic selection
- In the event of an ultrasound diagnosis of twin gestation, assess the dam's reproductive management in the following season

Measurement of vaginal length (shortened in the freemartin) was classically used as a guide, but PCR for Y-chromosome-specific sequences is now the method of choice for its sensitivity and early detection. Remember that some chimeric females remain fertile with reduced fertility: a positive result calls for diagnosis, not assumptions. Karyotyping remains useful in doubtful cases or in non-twin intersexuality.

1. Lillie FR. 1916, The theory of the freemartin. Science 43(1113):611-3. PMID: 17756274. 2. Ennis S et al. 1999, The diagnosis of freemartinism in cattle using sex-specific DNA sequences. Res Vet Sci 67(1):111-2. PMID: 10425251. 3. Szczerbal I et al. 2019, Droplet digital PCR as a new molecular method for a simple and reliable diagnosis of freemartinism in cattle. J Dairy Sci 102(11):10100-10104. PMID: 31447157. OMIA:000393-9913.