Triplets and absence of freemartinism
Keywords: ovine, sheep, triplets, freemartin
With the high incidence of multiple births, it is obvious that freemartinism is not usually a significant problem in sheep. In this set of triplets, two lambs were male and the third a female.
As is the case in bovine freemartinism, the lambs shared a common chorion, yet there was no evidence of suppression of the müllerian system in the female. See the uterus of the female at lower right. The males were normal and both had scrotal testes.
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The reason for a comparative lack of freemartinism in animals other than cattle is not known. Nevertheless, freemartinism does indeed occur in sheep, especially is large "litters" of four or more. However, in most studies the incidence is only about one percent in polytocous female lambs. Interestingly, freemartin lambs are highly masculinized; more so than bovine freemartins and often have gonads that resemble testicles, lacking oocytes altogether. Apparently, the müllerian system is so severely suppressed in some ovine freemartins that it is altogether absent.
Incidentally, freemartinism has been reported in many species but it does not appear to occur in horses.
Selected references:
Padula A.M. 2005 The freemartin syndrome: an update. Anim. Reprod. Sci.87:93–109
Smith K.C. et al 2003 Morphological, histological and histochemical studies of the gonads of ovine freemartins.Vet Rec 152:164-169.
