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Hybrid not Purebred – Dam not Sire!

Mares and foals running through the paddock

The Principles of Heredity in Horse Breeding

Mendel's Discoveries

Gregory Mendel (1882 -1884), an Austrian monk, discovered the fundamental principles of heredity around the year 1856. Mendel studied the results from crossing wrinkled-seed peas with round-seed peas and learned that one dominated the other. He learned that the pea has one gene for wrinkled-seed and a different gene for round-seed. Instead of the two types blending, they remained intact. Mendel thus formulated the law of segregation (the law of independent assortment) which explained how genes for different characters are inherited independently of one another. (Genes are the basic units of inheritance which store the genetic code for a species)

"Mendel's work laid the foundation for our understanding of heredity, and it's fascinating to see how his principles are applied in modern breeding practices."

Application to Horse Breeding

Federico Tesio's application of Mendel's principles to horse breeding is a great example of how scientific discoveries can be translated into practical methods. Tesio's focus on linebreeding and the concept of prepotency—where certain stallions and mares have a dominant influence on their offspring's traits—highlights the importance of understanding both dominant and recessive genes in breeding.

Hybrid Breeding Challenges

The idea that hybrids, such as racehorses, cannot breed true to type like pure species is crucial. This heterozygosity means that each foal can inherit a different combination of traits from its parents, leading to significant variability in characteristics like color, personality, and athletic ability. This variability is why even full siblings can be so different from each other.

Selective Breeding Strategies

Amplifying certain traits through selective breeding, by reinforcing specific sires and dams in the genetic pool, is a strategy to increase the likelihood of desired traits being expressed. The example of Northern Dancer, a highly influential sire in Thoroughbred racing, illustrates this well. By having multiple occurrences of Northern Dancer in a pedigree, breeders aim to increase the chances of inheriting his desirable traits, such as speed and stamina.

"It's all about managing the genetic pool to enhance the probability of producing a foal with the desired characteristics. This involves a deep understanding of genetics, careful selection of breeding pairs, and sometimes a bit of luck."

The Importance of the Mare

Quick Question: Why Is The Mare More Important?

Silly question right? Everyone knows that a foal receives 50% of their genetic code from the Sire and 50% from the Dam, so why would one sex be more important than the other? The easy answer is the sex chromosomes of the horse. Apart from being responsible for the normal sexual traits (maleness versus femaleness) sex chromosomes hold the key to the hormone system.

Indeed, the mare (or dam) plays a crucial role in the genetic makeup and development of a foal, particularly due to the influence of the X chromosome and mitochondrial DNA (mtDNA).

"While both the sire and the dam contribute equally to the genetic code of the foal, the mare's contribution through the X chromosome and mtDNA can have a more substantial impact on certain physiological traits that are critical for a racehorse's performance."

Case Studies

Tapit: A Genetic Powerhouse

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A great example of this is Tapit. Looking at the screenshots below of his pedigrees360 report we can immediately see that there is a very significant amount of mtDNA being passed down through the daughters in his pedigree. (This is highlighted in blue when the genetics are passed down through the daughters at least 33% of the time). The average number of blue boxes for stallions is 5, the great ones have 8 or more. Tapit has 10 which indicates that significant mtDNA has been passed down through the dams in his pedigree, almost twice as much as average – again remember, mtDNA is what drives the aerobic abilities of the resulting foal. The second chart below shows the amplification of breedshaping sires and dams within Tapits 9 generations. Again, significant amount of amplification of greatness.

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Violence: The New Super Sire

Let's look at new super sire Violence. He has significant duplication of breedshaping sires and blue hen dams in his pedigree, all which has led to him being extremely successful in the breeding shed. Consider how much more successful he would be if each mare was screened to ensure she was a good fit and not just a stud fee?

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Conclusion

Are you curious as to which Stallion is the best match for your mare for the 2025 breeding season or are you just shopping stud fees and hoping for the best? Pedigrees360 has a 74% accuracy rate in predicting the results of the matings ran on the site, where else can you get those kind of odds? Do you want to know which stallion will provide the largest amount of mtDNA for your foal, which Stallion will amplify greatness in the pedigree more than other stallions?

Send me the names of the mare(s) and their sire name and I will run your mare(s) against our stallions and if we are not a good match, we will find you the best match for your mare(s) at no cost to you.

Curious about how your mare(s) match up with our stallions? We offer FREE pedigree analysis reports utilizing state of the art software tools like G1 Goldmine and Pedigrees 360.
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