ADHIS recognised Factor XI as a single locus genetic defect that exists in Holstein cattle in 2003. For those Holstein bulls which have been tested, codes for the genetic defect are included in the Production ABV listing against their bull name. Bulls tested positive for a particular genetic defect are carriers of the defect. Bulls tested negative do not carry that particular defect.

Genetic Codes for Factor XI
Tested Positive - XI
Tested Negative - TX

Some Facts About Factor XI

There are 13 proteins in blood which take part in the blood clotting process. A deficiency in any can cause predisposition to bleed easily - known as haemophilia. In humans this disorder is caused by a deficiency of Factor VIII (occasionally Factor IX)

Tendency to Bleed

In dairy cattle a condition has come to light which is caused by a deficiency of Factor XI. Some cows with this deficiency have a tendency to bleed, for instance, after calving or at oestrus. Haemorrhaging or excessive bleeding can also occur during routine tasks such as de-horning & injecting, & even the pressure of teat cups during milking can cause bleeding. It has been shown that this condition is inherited when one, or both, of the parents carry the gene for this deficiency.

Just one undesirable recessive gene is not normally detectable in the carrier animal & is only seen when two carriers are mated (this, in fact, is the method used in the US to determine if an animal is a carrier of mulefoot - see diagram 2).

The Red & White Comparison

Breeders might consider the more familiar gene for red colouration in black & white dairy cattle. Only when a red carrier bull is matted to a red carrier female does the possibility of red offspring arise.

In the case of Factor XI, the carrier animal does sometimes exhibit signs of deficiency & furthermore is able to be identified by a blood test.

Thus, although it is classified as an autosomal recessive, it does not fall neatly into the classic recessive gene arena because carriers do sometimes show signs.

The Genetics

The genetics of Factor XI deficiency inheritance are simple. An animal received one copy of a gene from each parent. If one of those genes is that which causes the deficiency, then the offspring will itself be a carrier. Each parent has two copies of a gene so the offspring has a 50/50 chance of inheriting a faulty gene if one of the parents is a carrier,

The Chance of Normal Offspring

Even if both parents are carriers, normal offspring can be born, although the chance of the animal being a carrier are higher . You will note that some of the offspring could carry two copies of the faulty gene when two carriers are mated. Such double recessive animals have not been found in the general population & so far only exist in a research establishment. In practice, this condition is probably lethal, i.e. the animals carrying two copies of the faulty gene die perhaps at the embryonic stage, or soon after birth.

Reducing the Incidence

The genetics show that there is a simple but effective way of reducing the incidence of Factor XI deficiency in the national herd - that is to reduce the use of carrier bulls to a minimum, & eventually the number of carrier cows will be negligible.
Extracts from BFCS "Holstein Friesian Journal" & "Dairyfarmer"

Reprodcued courtesy of the HFAA