Horse evolution and genetics, particularly in the past 300 years since the development of the Thoroughbred by the use of Arabian stallions at the end of the seventeenth century, has largely been determined by the skill of the horse breeders.
Table of Contents (Horspedia)
The Effects of Horse Breeding on Equine Genetics (Thoroughbred Example)
In the case of the Thoroughbred, the emphasis has been on breeding in order to produce the unique combination of speed, stamina and beauty that are the strengths of the breed.
For most of the mainstream breeds, there are stud books of registered animals.
To ensure the continuity and purity of the breed, most breed societies conduct annual gradings of breeding stock and have strict requirements on entry to their registers so that all animals with papers meet not only the basic standards of height, colour and conformation but carry some of the more indefinable qualities that characterize the breed as well.
For those breeders less concerned with one particular breed and whose objects are to produce a certain ‘type’ of horse such as a hunter or event horse, the skills required in assessing the gene pool are no less exacting.
Creating a Horse Show Hunter and Horse Crossbreeding (Explained)
The dream of producing a show hunter that will win in the show ring at the top level is a project that can take years and several generations from the first pairing to get just right. The process of crossing breeds to produce good quality part-bred stock is most favoured around the world for the creation of riding horses.
A typical example of a well-known and sought after crossbred type is that of the native British mare (a New Forest and Connemara being typical examples) and a Thoroughbred sire.
The resultant progeny should be up to height but with good bone and should possess not only the sure-footed and calm nature of a native pony, as well as its intelligence, but also carry forward the stamina and bearing of the Thoroughbred.
Particularly in the Thoroughbred world, breeding to produce the best quality young stock that will carry the hopes and dreams of owners to the racetrack has long been something of a science.
The Science of Equine Genetics
At the top level, the Thoroughbred youngstock sales are still dominated by some of the world’s richest men. However, the fascination of breeding horses lies in its unpredictability it is not simply a question of pairing the best with the best to get the best.
The science of genetics is expanding apace in this modern era. The opinion is divided as to whether such advances are actually a good thing or not, but knowledge of the way in which heredity works can help to explain phenomena that our forebears could only observe and wonder at.
Why, for instance, can the mating of two bay horses produce a chestnut foal? Or why does the union of two champions not necessarily result in another?
Genes passed down from parent to offspring, are what shape an individual before the environment and opportunity enter the equation.
They have a definite physical existence, and there is a different gene for each discrete characteristic, for example, hair colour owned by every individual.
Every living creature has two genes – one from each parent for any given characteristic. Each of the parents, therefore, has an equal opportunity to shape his or her offspring.
Genes are carried like beads on a string on chromosomes, which are rod-like structures found deep within each of a body’s cells.
Chromosomes occur in pairs, and one member of each gene pair is located on each of the paired chromosomes. Each species has a characteristic number of chromosomes per cell. In the horse, this is 64, or 32 pairs.
Inherited Horse Genes (How Horse Genetics Work)
In each egg and sperm cell, there are only 32 chromosomes so that, when fertilization. occurs, the full complement is restored to the new creature, with one member of each. pair, together with its genes, coming from each parent.
However, when these germ cells are formed, the 32 single chromosomes are not handed on as an intact set exactly as they were inherited. Instead, a shuffling of chromosomes and even splitting and recombination of parts of pairs takes place, in a process known as ‘crossing over’.
The result is that each egg and sperm cell carries a random combination of genes, some derived from the father and some from the mother, which is different from that of any previous generation.
Although genes for the different characteristics are inherited separately, certain genes may have a tendency to be inherited together; this occurs if the genes are carried together on the same chromosome.
This phenomenon is not invariable, because crossing over can result in linked genes being separated. However, the closer the genes are on the chromosome, the less likely it is that such separation will occur.
In some species such as productive farmstock chromosomes have been mapped, and the position and identity of their genes have been established, but our knowledge of equine genetics- although improving is still in relative infancy.
Any progress that will aid health and soundness must be welcomed, but it should be remembered that the vast majority of horses are bred to perform and excel as individuals, not as producers of, for example, a uniform milk yield.
How Does Horse Genetics Determine Horse Coat Colour (Simple Explanation)
The way in which a character shows itself in an individual will depend on the dominant or recessive behaviour of the two genes (called alleles) in a pair. This concept is most easily illustrated by touching briefly on the inheritance of colour, the most instantly obvious physical characteristic of a horse.
Of the two basic coat colours – bay and chestnut the gene for bay is dominant, while that for chestnut is recessive.
Thus, a horse with two bay genes must be bay; a horse with a bay gene and a chestnut gene must also be bay, but a horse with two chestnut genes can only be chestnut (the technical term for what the eye sees is the phenotype; the underlying genetic ‘hard wiring’ is the genotype).
It follows that the mating of two chestnut horses can produce only a chestnut foal, but two bay horses can also produce a chestnut foal if both possess a bay and a chestnut gene, and if both happen and it is a random chance that decrees. this to pass on their Chesnut colour genes to their offspring.
Can Horse Colour Determine its Atheltic Ability? (Equine Abilities and Prepotency)
A horse’s colour is immaterial as far as its athletic ability or progenitive prepotency is concerned. In the past 50 years, 69 per cent of Epsom Derby winners have been bay, or its close genetic relative, brown – however, so have 69 per cent of Derby runners.
As an example, the superb Thoroughbred racing sire Sadler’s Wells is a double-bay genotype (and so cannot sire a chestnut foal), but there are numerous true-breeding bays that are bad stallions.
Observations about the way in which colour is transmitted can illustrate how other physical characteristics which may affect a horse’s performance are able to progress from generation to generation.
This makes it impossible for us to be dogmatic about the source of ability.
A Few Extra Fun Facts About Horse Genetics
- Sadler’s Wells, a superb racing Thoroughbred sire and an example of a double-bay genotype is incapable of siring a chestnut foal.
- Embryo transfer can be performed inside of the horse. In this procedure, the uterus (womb) of the mare, called the donor mare, is flushed with several litres of fluid. The recovered fluid is then searched for the presence of the embryo, which at this stage will be about the size of a pin-head.
- Stallion sperm can be stored for many years in liquid nitrogen. The semen is frozen in small straws and must be thawed in warm water before it is used.
- Stallion sperm cells are being examined under a microscope. Normal stallion sperm consists of a flattened, oval-shaped head attached to a long tail.