is a lot of merit in what Owner-Breeder terms "the Rasmussen factor". This
is a theory of "inbreeding to superior female families through different
individuals". The inbreeding to qualify must occur in the first five
generations and be carried in both sides of the pedigree. This is a theory I
find most agreeable and worthy of study.
Rasmussen wrote a series of articles that were reprinted in the Australasian
Bloodhorse Review between August 1996 and January 1997. The original
articles having been published in the American journal Owner-Breeder between
July 1993 and March 1994. These articles are recommended reading. A new book
has recently been published and if you do not have access to these articles
I recommend you read this publication.
Kalamoun is an example of a Rasmussen factor horse given in one of
the articles. There are many other examples of this pattern appearing in
successful sires and mares.
possible reason for this being successful is that it is believed genetic
material that sits closely together on the chromosomes is less likely to be
separated when recombination of this material takes place. It is possible
that certain stallions and mares that appear to be particularly prepotent
have in their chromosomes important genetic markers that sit closely
together and these are not separated when recombination takes place and
donít crossover, remaining fixed on their chromosomes and this has a
favourable results. That is, not all genes obey the law of independent
assortment. This may explain why the Rasmussen factor or for that matter any
other preferred pattern appears successful.
X Factoring the
prefer and use a variation of the Rasmussen factor. The step I take and
that I believe is worthwhile exploring is "inbreeding to superior female
families through different individuals SEX LINKED TO THE X CHROMOSOME". If
possible I would like to do this through full sisters on the X trail and
preferably through a son of one and a daughter of the other. Backline is one
horse I have bred that is an example of this type of mating. If this is not
possible the next best option is just to get a different strain of the same
female family on the X trail. I apply this pattern even though I know that
with a son the stallion will not pass on this strain of the X but for still
consider this as fitting my preferred pattern. With my pattern all that is
necessary is that in theory if a filly results a similar X chromosome can be
inherited from both the stallion and mare being mated.
merit of using different individuals is that it provides genetic variation
as each parent has its own unique genetic makeup. I believe Leo Rasmussen
has made a valid observation that it is desirable to breed to superior
female families through different individuals. It obviously multiples the
chances of inheriting the genes that make a particular family successful and
at the same time reduces the risk of inheriting genetic defects.
reason I would extend the Rasmussen factor to include "sex linked to the X
chromosome " is based on the premise that if important genes are carried on
the X chromosome then this is the only way they can be inherited. It is only
through the daughters or son's daughters that this genetic material is
transmitted. One other possible advantage sex linking this theory is one
could use individuals a lot further back in the pedigree chart. Not in the
literal sense as obviously you can only mate the immediate parents.
Please note when I refer to
the X trail or X factoring and similar I am not referring to the X Factor
theory of large heart inheritance. I attribute nothing specific to the X
chromosome and have doubts on the validity of the large heart being a trait
that is sex-linked.