LORI.bovine

Freemartins; vaginal measurements

Keywords:  bovine, vagina, hymen, freemartin, straw, speculum

Freemartins are common in bovine twin pregnancies. Freemartins are also seen in buffalo, occasionally in small ruminants and rarely in other species. When the sexes differ between individuals in twin or triplet pregnancies, female calves can be expected to be freemartins in 90-97 percent of calvings.  In rare cases, a male twin may die after its chorionic blood vessels have anastomosed with those of its female co-twin and the surviving twin may be born a freemartin.

Interesting historical aspects of freemartinism:  The discovery of freemartinism was attributed to the Scottish Physician and surgeon J. Hunter in his 1779 account of the Free Martin (click to enlarge): However, the basic descriptions of the cause of freemartinism has been attributed to Tandler and Keller in 1911. (Deutsche Tierärzt Wochenschr 19:148-149) and later, apparently independently, by Lillie in 1916 (Science 43:611-613).  Incidentally, the etymology of the word Free Martin, (later hyphenated as Free-Martin and finally written as freemartin) is open to much speculation but remains unknown.

In the case of a potentially valuable heifer calf being born co-twin to a male, one may choose to perform a PCR test* for the presence of Y chromosomes in leukocytes. This service is becoming common in North America.

A side note on chimeras: Less commonly used tests to diagnose freemartinism include karyotyping.  Freemartins are not only gonadal chimeras but hemopoetic chimeras as well (other organs may also be chimeric but this has not been well studied). This explains why freemartins continue to produce a mixed population of XX and XY leukocytes into adulthood. The author relied on this test for many years until it was shown that karyotyping is not an accurate method of diagnosing freemartinism unless a very large number of metaphase spreads are examined.

When the potential value of a heifer calf born co-twin to a male is not great, the simplest test for freemartinism is to measure the length of its vagina.

Figure 1: The length of the vagina in this mature heifer was 10.5 cm. One reported range of vaginal lengths in adult freemartins was 8 to 10 cm. Normal mature heifers have vaginas that are approximately 30 cm long. This heifer was born co-twin to a male, therefore it was highly likely to be a freemartins.  Size available: 843 x 1004px

An explanation: In early bovine embryos, anastomosis occurs between the chorionic blood vessels of twins lying adjacent to one another in the uterus. See this entry and another in LORI for additional details. In all female mammals, the Mullerian (paramesonephric) system develops from the endoderm. The interface between the endoderm and the ectoderm becomes the hymen. A normal vagina is comprised of a vestibule and cranial vagina, separated by the hymen. In embryos, only the section of the tract that is cranial to the hymen i.e. the Mullerian system is affected by Mullerian inhibiting hormone (MIH). Freemartins have ovotestes that contain Sertoli cells. Those Sertoli cells produce MIH, suppressing the development of Mullerian system. This leaves the vestibule of the vagina unaffected. For that reason, the majority of freemartins have normal vestibules but the cranial vagina is not patent. Therefore the length of the vagina (essentially just the vestibule) is short. In a very small percentage of all freemartins, the Mullerian system is only slightly suppressed, leaving cervixes and vaginas of normal length. Therefore the measurement of vaginal length is not infallible. However it remains a valuable rudimentary tool for the diagnosis of freemartinism.

The vaginal length of a normal heifer calf less than 30 days old is 13 to 15 cm. In freemartin calves the same age, it is only 5 to 8 cm long. Because a vaginal speculum cannot be used on such young calves, the author uses Cassou artificial insemination sheaths (regular sheaths for bovine AI guns) to measure vaginal length. Using a calf of comparable age to the suspected freemartin, a sheath is inserted into its vagina to its cranial extent then kinked at the level of the vulva lips. The same process is performed in the suspect freemartin and the two sheaths are compared, explaining the significance of the test to the farmer. See figure 2.

Figure 2: The sheath-kink test used to measure the vaginal length of a suspect freemartin calf. In two calves both less that 30 days of age, the sheath at left shows the likely presence of a freemartin calf. Size available: 1500 x 1055px

Naturally, the presence of a persistent hymen in a normal calf can confound the sheath-kink test but less than 1 percent  of heifers (approximately 0.8 percent in one large study) will be expected to have persistent hymens. A commercial probe is available to measure the length of vaginas but at far greater cost that a couple of disposable AI sheaths.

*Diagnostic tests for freemartins (PCR for Y chromosomes)

https://www.vdl.umn.edu/node/4396

https://www.geneticvisions.net/freemartin.aspx

Selected references:

Basile, J. R. and Megale F. 1974. Developmental abnormalities of genitalia of Zebu cows in the State of Minas Gerias. Argentina Biologica e Tecnologica 17:136-150.

Esteves, A. et al 2012  Freemartinism in Cattle in Ruminants. In: Anatomy, Behavior and Diseases. Ed. Marques, R.E. Chapter 7. pp.99-120. Nova Science Publishers, Inc. ISBN: 978-1-62081-064-4

Freeman, G. 2007 Explaining the freemartin: Tandler and Keller vs. Lillie and the question of priority. J Exp Zool B Mol Dev Evol. 15: 105-112

Hunter, J. 1779. Account of the Free Martin. Transactions of the Royal Society of London, 1779

Kästli, F. and Hall, J.G. 1978 Cattle twins and freemartin diagnosis. Vet Rec.102: 80-83.

McEntee, M. 1990. Ed. Reproductive Pathology of Domestic Mammals. Academic Press. ISBN 0323138047, 9780323138048

Padula, A.M. 2005. The freemartin syndrome:an update. Anim Reprod Sci 87:93–109