Mitochondrial DNA (mtDNA)
MtDNA is another form of genetic inheritance that is particularly fascinating and can possibly explain many questions that have so far gone unanswered.
Mitochondria are a tiny ring of hereditary material that lies within the cell but outside the nucleus of the cell. Mitochondria have their own DNA which has a different genetic code.
It is separate to nuclear DNA which is located in the nucleus of the cell and is passed on by both parents - and is inherited in accordance with mendelian genetics.
MtDNA comes only from mares - the stallion does not contribute any at all.
MtDNA is autonomous and is not subject to Mendelian inheritance. Nor is it rearranged in the process of meiosis and recombination - as is nuclear DNA - but it can undergo changes via spontaneous mutation, It all comes from the mares egg, never from sperm.
MtDNA contains different proteins to the DNA that is found in the nucleus of cells and it evolves at a rate that is ten times faster. MtDNA is passed on only by mares to both her daughters and sons - this is one reason why the dam of your chosen stallion is particularly important. The sons receive the MtDNA but they cannot pass it on - only his daughters carry this on
MtDNA has several important functions – the mitochondria produce a chemical called ATP which is the major source of energy for the cells and every cell in the body has thousands of these energy manufacturing plants. Mitochondria live in every cell, and they handle oxidative phosphorylation - the process that generates ATP. ATP powers muscle recovery, efficiency and endurance. It affects the power and maintenance of the horse's movement.
The main job of mitachondria is to produce energy - for the entire body - and for whatever function it is performing, including metabolism and physical exercise.
The mare plays a far more profound role in in producing champion horses and continuing winning families through the generations than was previously realised
The mares pedigree and her falling tail line is the main indicator of this inherited energy efficiency.
Alot of work is being done on this in thoroughbreds - but it is also an vital factor in Olympic sports.
The ability to create more ATP is necessary for the energy required in dressage jumping and eventing - requiring great muscle strength, oxygenation and the ability to sustain this.
Showjumpers are expected to jump off against the clock at great speed and may have to jump several rounds. A GP dressage test takes 8 - 9 minutes, with intense levels of collection requiring great oxygenation.
Eventers require more ATP than any other discipline having the 3 phases of dressage, cross country and showjumping to complete.
Research has shown that superior mitochondria can lead to more consecutive days of top performance levels and a higher capacity for endurance without tiring.
Superior mitochondria can give enhanced energy metabolism for sustaining high level repetitive movement in dressage and better oxygenation for faster recovery times.
It can prevent premature fatigue and maintain peak performance with engaged movement during a rigorous training session or competition.
Specific mitochondrial variants have also been associated with better rideability and higher breeding values for gaits.
Mitochondria affect tissue development and repair and are important for recovery of physical stress and competition.
It could be that some mare families have far superior mtDNA and this could be why they can consistently produce licensed stallions, great broodmares, and top performance horses from different stallion lines.
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Ken Mclean says “it is from the mitochondria that the cell receives the energy to work the bio machine”
MtDNA is responsible for many vital functions - it drives respiration rates, energy conversion in the cells and during exercise, the production and distribution of energy to sustain the work of the muscles. It also has an effect on heart size and thickness of the heart walls.
Aerobic energy production takes place in the mitochondria.
As the horse is at least 60% muscle, this has major implications for performance – genes linked to muscle mass have a major impact on athletic performance. Mitochondria provide energy for muscle contraction and the larger quantity of mitochondria per unit of muscle weight leads to the oxidative capacity of the muscle being greater
MtDNA does not influence conformation or bone and joint angles - these are determined by nuclear DNA from both parents. The mitochondria does however influence how the horses structure develops and its ongoing maintenance (Heidi Schlenker).
If the mare has superior mtDNA this could provide an edge with utilising energy for muscle growth and balance, and tissue repair - this could lead to progeny being able to build better top lines, strong loins and the ability to hold themselves in proper self-carriage without the rider having to "hold" the horse together so much with constant leg and rein aids to engage the hindleg and raise the forehand. The horse will naturally hold itself in a frame and power itself along more easily. Better energy for muscle growth and repair is crucial for top level sport
Superior mitochondrial MtDNA can significantly affect the uterine environment - such as gestation length and nutrition in the uterus- foals may grow more evenly and lead to less developmental issues. It also may affect embryo survival - the superior mitochondrial function in the oocyte is linked to better embryo survival rates in foals.
Research shows that mitochondria and the uterine environment factors account for 11 - 39% of performance variation (Borkowska) - Heidi Schlenker.
Superior mtDNA of course will not trump bad conformation and other flaws which are passed on by nuclear DNA.
The mitochondria rather can power the movement that is possible within the confines of the horse's natural conformation. The best results will come from mares with correct and sound structures and superior mitochondria. (Heidi Schlencker / Volturi site on Quaterhorse breeding)
Ongoing work is being done in thoroughbreds in organising these MtDNA families into recognisable haplotypes – which are a set of DNA variants on a single chromosome that tend to be inherited together. This could give the impetus for the same to be done for warmbloods in the future
Dr Matthew Binns in the book Thoroughbred Breeding Theories said “ it is apparent that MtDNA variation can not only limit elite performance but that ancient MtDNA adaptive polymorphisms may be directly affecting maximum performance capacity.”
These haplotypes remain relatively unchanged for thousands of years and have been found, in the different families, to trace back to a single source. It can be a single gene or consist of multiple genes. It can trace to a tap root mare and then branches out through her progeny
A study was done on this in Holsteiners and their aptitudes for dressage and showjumping ability ( Research Gate ) Estimated breeding values were used to classify the mtDNA into haplotypes with a particular aptitude for dressage or showjumping. All mares within a lineage showed identical haplotypes in the non synonymous variants.
Showjumping and dressage are very energy demanding and rely on aerobic capacity. It is reasonable to assume that the variation in mitochondrial genes could have an effect on performance.
A pronounced dressage ability was attributed to 24 lineages of haplotype B with higher estimated breeding values in dressage, gaits and rideability.
In studies in humans, 18 mitochondrial genes have been shown to be associated with fitness and performance phenotypes. Studies show great potential of mitochondrial association and the importance of mitochondrial variation for performance traits.
In general, studies are so far lacking in meaningful and useful results in warmblood and other breeds that compete in the Olympic disciplines.
Studies have also shown that heritability of racing performance between mares and foals is much higher than between sons and foals, - indicating the difference could be in the inheritance of mtDNA and sex linked genes. This is the same for all breeds of horse, the mare line is revered in all types of horses bred for different sports including quarter horses , standardbreds and arabs
Alan Porter said “There is definitely something that goes on with stallions and mitochondrial female families. I see too many examples on pedigree charts where there are several good horses from the one mitochondrial haplotype, by the same sire or sire line, and where they are sufficiently distant in pedigree terms that one would not have influenced the other”
Great breeders have always said that you need the power of a good female family - and perhaps it is because particular families have far superior mtDNA to pass on - and have done so reliably over many generations.
Top breeders have always instinctively known that the female's influence is far more important - even if they didn't know why
Mares are the genetic powerhouse that can be the determining factor in success - and breeders of all animals and horses in all disciplines have long sought after females and proven producers from top winning families.
Ken Mclean " Around the world the most successful farm operators are active at acquiring quality mares and fillies - they know maternal strength is the pathway to success"
Ken Mclean says " it is from these mares that tomorrow's best colts will be born"
Madame Vuillier - consultant to the Aga Khan said "It is always the mare which improves the stallion, and not the stallion which improves the mare"
Perhaps we need a paradigm shift - and should be looking at pedigrees and female lines in a different way . The current model has been traditionallly predisposed toward the stallion and truthfully - to commercial stallions and popularity. New research and evidence in different areas could indicate we should widen our search in the effort to breed better horses
Ken Mclean " The long term success of any serious breeding program lies squarely upon the shoulders of the females of the line - and not one in 10 000 breeders have yet fully understood this fact"
There have always been elite mares in various studbooks and "blue hens" in racing, and these superior producing mares most likely inherited special mtDNA from their direct female line of descent.
These great mare families seem to be able to transmit that something extra to their progeny - and horses with this special mtDNA could be physically able to perform better than their peers - given the right environment
There are some rare horses that are streets ahead of their contemporaries - they are in a class of their own - they simply transcend others with their inherent unique intangible qualities - they are vibrant, sparkling, energetic, vital - what is the source of this vitality - is it a combination of unique genetic traits or something about their biomechanics that allows this vitality to shine - and could it have something to do with superior MtDNA and / or factors carried on the X chromosome?
Some horses have much greater talent and reserves of energy -does this contribute to more flamboyant movement? Some horses are simply capable of so much more - they have greater reserves of energy, the way they can perform certain movements with ease , or be able to mobilise that energy with greater speed for jump offs against the clock
They reach higher levels of education in a much shorter time frame, and the work is easy for them to execute with fluid flowing efficiency -They may achieve fitness more quickly, and recuperate faster from the energy outputs - leading to greater strength and durability for training sessions
If MtDNA dictates the availability of energy then it could also be sparking this ' vitality"
"MtDNA transcends sire trends and hype .Elite mare families produce multiple champions over generations, they have repeated success through their daughters, produce broodmares that upgrade stallions and are a consistent presence in elite pedigrees. " Heidi Schlenker
These superior mare lines are the backbone of breed shaping bloodlines and very highly represented in top sires and champion performers.
Heidi Schlenker says when a horse is not from a good family, the breeder is dependent on flash sires, isolated incidents of performance and will have limited broodmare impact.
MtDNA has a stronger impact on ability than paternal genetics - it creates champion stallions and elite broodmares when crossed with different sire lines. It makes fillies that are not just great performers - it builds them to be future producers of talent.
Ken Mclean says " with the heritability of sex-linked genes and MtDA - dams have greater influence on their progeny and sires have a greater influence on their daughters."
Apparently the mtDNA must also be a good match for the nuclear DNA contributed by both parents and this is important in planning matings
Perhaps we should be paying a lot more attention to the dam of a stallion and her own female family rather than focusing so much on spectacular stallions themselves.
Taking all this into account - trying to concentrate very important foundation mares and mare families in our pedigree designs could be a wise thing to do. We want to increase the number of genes supplied by these elite mares and mare families in our foals and breeding programs
Examples - Sky Diamond
Baumanns Diorella
Quaterhit