Has anyone EVER had or have HEARD of one of these types of mares becoming pregnant with homone support therapy?
I have found a study paper that studied these mares and developed 'classes' or "types" of deformity with this karotype. Class I, being mostly normal in terms of reproductive organs, but maybe small ovaries. Type IV being mostly deformed and usually having a testicle up inside that required removal, or no uterous etc. The paper stated that there were cases of Type I horses becoming pregnant, although rare.
The vast majority of these mares will not be developing follicles and/or ovulating, and therefore will not be able to be bred, let alone get pregnant and carry a foal.
The most commonly encountered dysgenesis is the 63,XO gonadal dysgenesis where only a single sex chromosome is present. It is analogous to Turner's syndrome in humans. these animals will usually have an underdeveloped female reproductive tract with - quite literally - pea-sized non-functioning ovaries. Interestingly in humans with this condition pregnancy may occur, but almost invariably (99%) results in early pregnancy loss. All reported cases in the equine however have failed to produce pregnancy.
It has been suggested that a 63,X dysgenesis may retain a degree of fertility (Power, 1987).
65,XXX (pure trisomy of the X chromosome) is rare in the equine (11 cases reported to date) and universally infertile.
There are several other true chromosomal imbalances that are less commonly encountered.
Mosaicism or chimerism involving the sex chromosome (usually the X chromosome) are seen, most commonly 63,X/64,XX, which is the second most commonly seen aberration of the sex chromosome in the equine.
As all of these conditions affect the chromosomal value of the animal, and as a chromosomal balance is required to achieve fertilisation and resulting maintained pregnancy, the vast majority of these animals are going to be infertile, or if pregnancy is achieved lose the pregnancy early (although I suppose one should never say never!!! ). As they are chromosomally affected, use of exogenous hormones is not going to be beneficial.
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