Popular Sire Syndrom

A sire is highly sought after by breeders if the animal itself is outstanding, in the hope that its special traits will also be passed on to its offspring. It is then given priority for breeding.

In this way, a single stud dog or stallion can sire hundreds or thousands of offspring within a short time, while other sires are hardly used. If his sons are also in demand, the effect is amplified over several generations.

It becomes particularly problematic when the daughters of the popular sire are also preferred for breeding. His genetic material then enters the following generations through both the paternal and the maternal side, and his descendants inevitably end up being mated with each other. In the end, entire populations trace back to a few ancestors despite a large number of active breeding animals, and show correspondingly high inbreeding. The large number of breeding animals then masks the genetic diversity that is in fact low.

• Loss of genetic diversity: A large part of the population's genetic material goes back to a single animal. The effective population size, a measure of the genetically effective size of a population, depends strongly on the number of sires actually used and decreases accordingly. In the individual animal, this shows up as lower genomic heterozygosity.
• Rising inbreeding: Just one generation later, many breeding animals are half siblings. Matings between relatives can then hardly be avoided, and the genomic inbreeding coefficient of the offspring rises.
• Spread of hereditary diseases: Every animal carries a few recessive disease variants without being affected itself. If a popular sire carries such a variant, he passes it on to about half of his offspring. If these are later mated with each other, affected animals appear. The variant is often only noticed once it is already widespread.

The Quarter Horse stallion "Impressive" (born 1969) was in great demand because of his pronounced muscling and had a large number of offspring. He carried a mutation in the SCN4A gene that causes Hyperkalemic Periodic Paralysis (HYPP). The variant is inherited dominantly. Because carriers are often particularly heavily muscled, they were additionally favoured in breeding selection, and the mutation spread widely among the descendants of Impressive (Rudolph et al. 1992).

Today, the American breed association AQHA requires an HYPP test for descendants of Impressive; homozygous affected horses (H/H) are no longer registered.

• Limit the use of individual sires. In its international breeding strategies, the FCI recommends that a stud dog should not have more offspring than corresponds to 5 % of the puppies registered in his breed over a period of five years.
• Test sires before intensive breeding use for the hereditary diseases known in the breed.
• Take relatedness into account when planning matings, for example with the genomic inbreeding coefficient (GIC), genomic heterozygosity and ROH profiles.
• Use many different sires, including sires from less well-known lines.

With a genome-based inbreeding analysis, Generatio determines the genomic inbreeding coefficient, the genomic heterozygosity and the ROH profile of an animal. The values show how strongly an animal is already shaped by inbreeding and serve as a basis for mating planning.

Single tests:

• Dog:Inbreeding & Diversity (Fitness) Dog
• Horse:Inbreeding & Diversity (Fitness) Horse
• Camelids:Inbreeding & Diversity (Fitness) Camelids

Bundles including inbreeding analysis:

• Dog:SNP Profile Identity & Inbreeding & Fitness Dog: DNA identity and inbreeding analysis
• Dog:ProLine Bundle Dog: DNA identity, inbreeding and diversity analysis and breed analysis
• Horse:Bundle Breed Analysis, Identity, Inbreeding Assessment
• Horse:MIM-6-Var. plus Inbreeding & Fitness: test for the six MIM variants and inbreeding analysis
• Dromedary:Bundle DNA Identity and Inbreeding Analysis Dromedary

Lexicon:

• Hyperkalemic Periodic Paralysis (HYPP)
• Genomic Inbreeding Coefficient (GIC)
• Genomic Heterozygosity
• ROH Profiles

Literature:

• Rudolph, J.A., Spier, S.J., Byrns, G., Rojas, C.V., Bernoco, D., Hoffman, E.P.: Periodic paralysis in quarter horses: a sodium channel mutation disseminated by selective breeding.Nat Genet 2:144-147, 1992. DOI: 10.1038/ng1092-144
• Leroy, G., Baumung, R.: Mating practices and the dissemination of genetic disorders in domestic animals, based on the example of dog breeding.Anim Genet 42:66-74, 2011. DOI: 10.1111/j.1365-2052.2010.02079.x
• FCI: International Breeding Strategies (Fédération Cynologique Internationale).