Horse Genetics for Speed Paul R Earl Facultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL 66451, Mexico
PrologueHorse genetics including systematics and phylogeny, the genetics of morphologic traits, color variation and the inherited diseases, molecular genetics, immunogenetics, genetic aspects of diseases, cytogenetics and gene maps, linkage and modern breeding technologies, behavioral and developmental genetics, genetic conservation, the genetics of performance traits, conformation, locomotion and physiological traits, genetic improvement and standardized genetic nomenclature for the horse are all touched on in The Genetics of the Horse by Ann T. Bowling & A. Ruvinsky, Editors, CAB Inter-national, Wallingford, UK, 2000.
Horse evidence supports Darwin-Wallace evolution by an infinite number of small changes through millions of years. Welcome macroevolution, even though it is absent in horses! “Sports” by breeders fit macroevolution—giant steps! Equine paleontology strongly supports classic microstep evolution as put forth by Ronald Fisher (1930), thousands of other biologists and the educated public. .In paleontology, the horse is by far the best documented mammal. Regardless, Hollywood puts the Roman army on horses when they only had ponies!
The horse sequence from early Hyracotherium (4 toes on each front foot, 3 on hind feet) to living Equus traces the loss of toes, skull changes and size increases that characterize horse evolution. Vestiges of the first & second toes still exist as splint bones on the cannon bones. The evolution of modern horses is linked to the spread of grasslands in the late Tertiary epoch. Equus arrives 4 million years ago, the genus of all modern equines. The evolutionary aspects were first worked out in the late 1800's and involved people like Thomas Huxley. The evolutionary sequences provides the most classic example of dramatic longterm evolutionary change within a lineage with the rise and fall of branching species, one replaced by another..
When paleontologic horses started to become runners, there was a simultaneous increase in body size, leg length and length of the face. The bones of the legs became fused together. The leg bones and muscles became specialized for efficient to-and-fro strides, without flexible leg rotation. Horses stood on tiptoe thus adapted for speed. Their weight was supported by elastic ligaments that ran under the fetlock to the big central toe (coffin bone).
Speed depends mostly on the integrety of the legs. In the illustration of Bull Lea you see that his front tendons are a little bowed. Overexcercise must lead to inflammation such as inflammation of the suspensory tendons. A bowed horse had muscles SO STRONG that they uprooted the ligaments from the bone. Of course, these suspensory tendons will reset, yet not as good as new.
Order Perissodactyla, Family Equidae, Genus EquusThe taxonomy of horses, donkeys and zebras is a start for genetics as the study of the earliest equids is another and anatomy another.Equus burchelli, the Plains zebra of Africa Equus zebra, the Mountain zebra of South AfricaEquus grevyi, Grevy's zebra, the most horse-like zebra. Equus caballus, the true horse, which once had several subspecies. Equus hemionus, the desert-adapted onagers of Asia & the Mideast, including the kiangEquus asinus, donkeys of northern Africa.
The real environmentFixed races, scandal, insurance fraud, high finance in the millions of dollars and murders like the Woodward accident mark the horse industry and the millionaire horsey set. Certainly, a few progeny have “replaced” sires—perhaps the teaser. Horse games are a form of entertainment, chisling and bribery in which the servants, stealing what they can, perform for royalty possibly in the present form of moviestars who have replaced many of the millionaire families of a century ago. This much is clear.
Genetics starts hereEven sires like Native Dancer, pulled in the Kentucky derby!, are inbred. The antique suggestion is “Breed the best with the best,” yet good performers arise at random—often. The reason that there is no real trend in most sires is that they are rather close to being copies of each other. Talk of compatability, doses, nicks, line breeding and so on is only part of a mystique.
When the rank of the horse is compared to the year, no correlation is derived. This means that the breed has not improved in 100 years, despite Secretariat being rather remarkable. One can add that Hancock, Woodward Senior and others paying $125,000 to import the sire Sir Gallahad III in the 1920s reinforced inbreeding through breeding the best with the best..This—at random—is a rather strong statement, disturbing for the little old ladies who are pouring over horse pedigrees as if they were founding a new religion. Do you expect the greatest performer Secretariat also to have been the greatest sire or grandsire or specialist broodmare sire? Things don’t work that way, do they ?
Plucky Liege was one of the most important broodmares of the 20th Century. Two of her sons, Sir Gallahad III and Bull Dog were leading sires in America, and 2 others, Bois Roussel and Admiral Drake were sires of classic winners in England, Ireland and France. Plucky Liege produced 12 foals in all, 11 of which were winners, and 6 of which won stakes, including 2 classic winners. Five foals were sired by Teddy.As so common, a leading broodmare sire Mr Prospector 1970, Raise a Native out of Gold Digger by Nashua has Teddy on the male and female lines of his pedigree.
ACE, the angiotensin converting enzymeThis enzyme has the hilarious speed gene that never will prove out.. Nonetheless, ACE is much better than nothing, though quite out-of-place since it is studied as relating to hypertension and myoinfarctions in humans. Sports medicine is not yet extended to racehorses. This gene is involved in human arteriosclerosis and hypertension. Someone of bottomless ignorance has confused blood pressure with the functionality of the legs as limiting for SPEED in racehorses.
From quite a different view, all variables of all kinds are testable very easily in every race, fixed or unfixed. Run the horse races in analysis of variance (ANOVA). The problem here is different: finding insertion/deletion polymorphisms in ACE genes in horses that do indeed have distinct athletic abilities. Can genetic and environmental risks be told apart in relation to cardiac difficulties such as the mitral valve problems in certain few horses? We’ll wait and see.
The impression is that the enormous nucleotide sequencing power of today’s genetics is going to be used to rip off the breeders that are foolish enough now to pay $150,000 stud fees for carboncopy stallions. The Sittingbourne Research Centre in Kent, UK offers DNA screening tests that identify specific characteristics relating to trainability, performance and soundness, even identifying optimum track distances for individual horses. Isn’t that nice?
What is Bull Lea telling us? Legs not lungs.He was bowed in BOTH legs. Speed causes some loss of function, yet of course not his “best sire” genetics. ACE came over from human sports medicine. Do those people need hypertension ? ? ? At this point please note that emboli floating about are likely to be filtered out BY THE LEGS. The danger for horses seems to be the ignorant and fraudulent nature of the ACE promoters.The forelegs are like puppets on strings pulled from the shoulders. That pull is so very great, it can pull the ligaments off the bones.
Blood volume expansion together with muscle movements and increased intrathoracic pressure, supplements venous return and increases atrial and myocardial fiber stretching and pressure. Exercise increases the plasma levels of many hormones like endorphin, arginine vasopressin, cortisol, catecholamines and the hormones of the renin-angiotensin-aldosterone system, especially ACE. These are hormones involved in the control of cardiovascular function and fluid balance as well as with stress and relief from pain. See ”The ACE gene and muscle performance,” Nature, vol. 403, p. 614, 10 February 2000.
To understand how variations in the ACE gene might influence how you run, you need to know what ACE does. Angiotensin is present in the blood. Under certain conditions, the kidneys secrete the hormone renin into the blood which cleaves a 10-aminoacid protein from angiotensinogen to form the compound angiotensin I. ACE can knock 2 aminoacids off angiotensin I to form angiotensin II. Angiotensin II has several functions. It directly increases blood pressure by constricting arteries. It indirectly raises blood pressure and blood volume by stimulating the thirst centers in the brain and directing the kidneys to conserve more minerals and water.
Altering vascular tone considerably influences blood pressure.ACE inhibitors relate to lowering hypertension and reducing heart failures. Their beneficial effects can be attributed to blocking the production of angiotensin II from angiotensin I.There are alternative enzymes capable of converting angiotensin I into angiotensin II like chymase. Many OTHER FACTORS like bradykinin as a vasodilator are involved in controlling the circulation like pulse rate and air flow respiration. Certainly, more than one gene calls for investigation !
What else do we need to know? The pulse and the arterial saturation percent of OXYGEN. These variables (never reported! ?) by oxymeter are common to human and NOT to veterinary medicine. Incidentally, red blood cells can be both nutritionally and hormonely increased. That is packed cell volume can be most easily tested. AGAIN, deworming helps. Many variables are easy to obtain continuously. Treadmills and various other devices, variables and tests are used little.
The inhibition of ACE reduces hypertension.What the speed gene people are saying is that if the heart works even harder, more races will be won. Will the ligaments fly off the bones before the heart attacks ? What is human and what is equine and what is normal and what is pathologic are being confused by people who just don’t know. More: much information is missing. Is ACE an undetected racing dope ? Or better: Would it work? You can bet it’s been tried unsuccessfully in horses. When will ACE reports on humans from the Athens Olympics be available ?