Selective Mating Definition
By Loren Bolinger, January 30, 2005 version, Tuesday, August 01, 2006
Selective Mating [of Thoroughbreds] Definition
“…since the writings of Charles Darwin and Francis Galton … domestication is the selective
and purposeful breeding of animals in captivity to produce animals adapted to human-made
environments. ”
Selective mating for the
Thoroughbred is defined as the intentional selection of mates to be
bred based on the collective and harmonious combination of certain,
specific, genealogical patterns of ancestors, temperaments , and their
anatomical proportions that are most likely to produce the expression
of performance traits in the offspring. The parents of a mating,
breeders believe, should have demonstrated racing performance. Often,
other goals of selective mating practices include minimizing and or
repairing genotypic and/or phenotypic faults or flaws so that the
resulting progeny are improved or less flawed than the parents.
Another, often ignored factor is the responsibility to cull stock that
fails to meet expectations in performance and anatomical proportions to
minimize the number of failures that enter the breeding population.
Selective mating is the
process by which intentional selection of individuals with desired
traits or characteristics are mated in a systematic way such that those
traits or characteristics have a higher likelihood of being transmitted
to their offspring and subsequent generations in a breeding program.
The purpose is to increase predictability and transmission of desired
traits and to reduce variability.
In the process of selective
breeding, intentional decisions made by the breeder in which those
individuals having traits that allow them to exhibit superior racing
performance and transmit those traits to their progeny are identified
and preferred over those less able to win and transmit winning traits
to their progeny. In the course of the number of generations of race
horses that a breeder will produce in his lifetime, as his knowledge
and confidence increase, there can be a progressive tendency for the
astute breeder's entire breeding stock to upgrade or increase their
[cumulative or] overall degree of winning performance.
Reinforcement
The expression of desired
traits and characteristics is primarily accomplished through inbreeding
reinforcement. Powerful, positive reinforcement factors include the
duplication of ancestors, combination of ancestors, or patterns of
ancestors in order to cause expression of overt and latent traits
carried within the genome. Reinforcement can also be accomplished
through genomic combination [combining sirelines, ancestors, and/or
matrilines (female families). Conformation Fault Compensation is the
repair and/or improvement of parental flaws in the offspring and among
some bloodlines can be an additional, desirable attribute of nicking.
Phenotypic combination occurs when parents with compatible phenotypes
are mated. Phenotypic similarity, as with symmetry is a golden rule of
nature and breeding racehorses. Sophisticated mating selection is often
based on sex-linkages of certain ancestors or can be based on the
desired sex of the target, itself.
Sex-Linked Selection
Sex-linked selection methods
are those in which mate selection is based on the sex of specific
ancestors in the pedigrees of the mates and/or the sex of the target
individual. In a number of selective mating methods, the sex of
specific ancestors and/or the sex of the target is important to achieve
the desired results or increase the probability of obtaining the
desired results. Coordination of the sex of ancestors in selective
mating schemes is usually made in conjunction with the duplication of
key ancestors. Increasing probabilities of obtaining prepotency and the
resulting expression of performance traits by early breeders was most
successfully accomplished through sex-linked inbreeding of certain
ancestors. These ancestors were commonly acknowledged [recognized] by
many breeders as having desirable, heritable characteristics and a
predisposition for passing their characteristics on to subsequent
generations compared to the mean for the breed.
A potential problem of
sex-linked selection is that the sex of the TARGET cannot at this time
be predetermined or pre-selected. The breeder may select methods
optimal for producing a male but incorrect for a female or vice versa,
then have the incorrect sex foaled for the method chosen.
Selection, avoidance, and culling
Selection, avoidance, and
culling involve the continued elimination, avoidance and/or attenuation
of undesired traits and characteristics in breeding stock that leads to
poor performance or increased variability [that is, a lower likelihood].
The Breeder's Rejection and Culling Process
During
the selection of mates, decisions must be made by the breeder that
identify and reject breeding stock that have the semi-independent
variables of poor ability to win and low ability to transmit winning
traits to their progeny. In this way the breeders’ chances of
success are vastly increased. By rejecting those perceived to be unfit,
the probability of production of progeny exhibiting superior racing
performance will improve. Better racehorses produced by the breeding
program obviously improve the breeders’ chances of economic
survival and satisfaction. By being highly selective over his lifetime
of breeding horses, the breeder's efforts have a progressive tendency
to increase the overall degree of successful performance in his
offspring.