Sukusiitoksella tarkoitetaan todennäköisyyttä sille, että yksilö saa satunnaisesti valitun geeniparin molemmat alleelit samalta esivanhemmalta. Sukusiitos vähentää yksilön heterotsygotiaa ja lisää homotsygotiaa, jolloin myös resessiivisten alleelien ilmeneminen yleistyy. (Suomen Kennelliitto.)

Sukusiitosaste voidaan esittää prosentuaalisesti sukulaisuussuhteita vertaamalla. Sukusiitosaste on puolet vanhempien välisestä sukulaisuussuhteesta. Serkusparituksessa sukusiitosaste on 6,25 %, puolisisarparituksessa 12,5 % ja isä-tytär/emä-poika tai sisarparituksessa taasen 25 %. Tämä prosenttiluku tarkoittaa myös prosentuaalista mahdollisuutta sille, että jokin resessiivinen ongelma tulee esiin parituksen tuloksena. (Suomen Kennelliitto.)

Tutkimuksissa on huomattu, että yli 10 % sukusiitosasteen jälkeen mahdolliset haittavaikutukset alkavat ilmenemään yksilössä. Tällöin myös yksilön hedelmällisyys ja elinvoima heikkenevät, jota kutsutaan sukusiitostaantumaksi. Suomen Kennelliitto suosittelee, että neljän-viiden sukupolven perusteella laskettu sukusiitosaste pysyisi vielä alle 6,25 % (vastaava sukusiitosaste kuin serkusparitus). Koska jokainen yksilö kantaa perimässään useita haitallisia alleeleja, niiden todennäköisyys tulla esiin kasvaa myös sukusiitosasteen myötä. Turvallisia sukusiitosyhdistelmiä ei ole olemassa. (Suomen Kennelliitto.)

​Jos halutaan laskea mahdollisimman totuudenmukainen homotsygotian ja sukusiitoksen aste yksilölle, tulisi käyttää kaikkia mahdollisia sukupolvia laskennassa mukana. Sukusiitosasteen laskemiseen tulisi siis aina sisällyttää kaikki mahdolliset sukupolvet kantakoiriin saakka, tai ainakin sinne asti, minne tietoa pystytään löytämään. Kaikki puuttuva data johtaa aina aliarvioon todellisesta sukusiitosasteesta. Vain viiden sukupolven käyttäminen sukusiitosasteen laskemiseen on erittäin harhaanjohtavaa, sillä yksilöllä voi viiden sukupolven mukaan laskettuna olla sukusiitosasteena ”vain” 6 %, mutta 30:n sukupolven mukaan laskettuna se onkin jopa 25 %, mikä vastaa geneettisesti sisarparitusta, vaikka yksilö ei itse olisikaan sisarparituksen tulos. 6 %:n ja 25:%:n mahdollisuuden ero resessiivisten, haitallisten geenien siirtymiseen on suuri, ja tämän vuoksi kaikkia mahdollisia sukupolvia tulisi käyttää sukusiitosasteen laskennassa, jotta todellinen riski tiedetään. (Beuchat 2014.) 

Inbreeding refers to the probability that an individual receives both alleles of a randomly selected pair of genes from the same ancestor. Inbreeding reduces an individual’s heterozygosity and increases homozygosity, so the expression of recessive alleles also becomes more common. (Finnish Kennel Club.)

The degree of inbreeding can be expressed as a percentage by comparing kinship relationships. The degree of inbreeding is half of the consanguinity between the parents. In first-cousin mating, the inbreeding rate is 6.25%, in half-sister mating 12.5%, and in father-daughter/dam-son or sibling mating it is 25%. This percentage also means the chance that a recessive problem will emerge as a result of the mating. (Finnish Kennel Club.)

Studies have noticed that after an inbreeding rate of more than 10%, possible adverse effects start to appear in the individual. In this case, the individual’s fertility and vitality decrease, which is called inbreeding stagnation. The Finnish Kennel Club recommends that the inbreeding rate calculated on the basis of four to five generations should remain below 6.25% (the same inbreeding rate as a cousin mating). Since each individual carries several harmful alleles, the probability of their emergence also increases with the degree of inbreeding. There are no safe inbreeding combinations. (Finnish Kennel Club.)

​If you want to calculate the most truthful degree of homozygosity and inbreeding for an individual, you should use all possible generations in the calculation. When calculating the inbreeding rate, you should always include all possible generations up to the base dogs, or at least up to the point where information can be found. Any missing data always leads to an underestimation of the true inbreeding rate. Using only five generations to calculate the inbreeding rate is very misleading, because an individual can have an inbreeding rate of ”only” 6% based on five generations, but calculated by 30 generations it is up to 25%, which is genetically equivalent to sibling mating, even if the individual itself is not the result of sibling mating. The difference between a 6% and a 25% chance of passing on recessive, deleterious genes is large, and therefore all possible generations should be used in the inbreeding calculation to know the true risk. (Beuchat 2014.)

​​According to The Kennel Club of Great Britain, the average inbreeding rate of the Shetland Sheepdog population in their registry calculated in September 2022 is 7.5%.

In a study that processed genetic data obtained from Wisdom Health Genetics from different dog breeds, the average genomic (i.e. DNA) inbreeding percentage of Shetland Sheepdogs was calculated to be 29.2% (Bannasch et al. 2021).

​In the US study, blood samples were collected from AKC registered Shetland sheepdogs and their genomic pedigree was examined from SNP data (single nucleotide polymorphism) and WGS data (whole genome sequencing). The average genomic inbreeding percentage was 38.6% with SNP data and 35.4% with WGS data. (Dreger et al. 2016.)

The inbreeding percentages of ROM-awarded Shetland Sheepdogs have been studied in the United States. The data covered both bitches and males born between 1931 and 1992 and achieved the ROM title (register of merit, the male has at least 10 and the female has at least 5 champion offspring). The average inbreeding rate for all ROM awardees was 32% (Bowling a). According to the research, every ROM Awarded Shetland Sheepdog is genetically related to another ROM Awarded Shetland Sheepdog as if they were littermates. This suggests that the gene pool of the top-performing Shetland Sheepdogs in the United States is not very large, even though the number of individual dogs in the population is large. (Bowling 2010.)

​The average inbreeding value of Shetland sheepdogs born in Finland in 2021 calculated with 30 generations was 22.9646 % (minimum 13.0452%, maximum 38.0587%). There was an average of 82% of relatives known in the pedigree (minimum 71%, maximum 90%). The research I wrote about this can be seen in Finnish above.

The average inbreeding value of Shetland sheepdogs born in Finland in 2022 calculated with 30 generations was 23.0149 % (minimum 13,2302 %, maximum 38,3268 %). There was an average of 83,63 % of relatives known in the pedigree.

The average inbreeding value of Shetland sheepdogs born in Finland in 2023 calculated with 30 generations was 22.8016 % (minimum 13.2860 %, maximum 36.7743 %). There was an average of 85,03 % of relatives known in the pedigree.

Bannasch, Danika ym. 2021. The effect of inbreeding, body size and morphology on health in dog breeds. Canine Medicine and Genetics 8:12. https://cgejournal.biomedcentral.com/articles/10.1186/s40575-021-00111-4

Beuchat, Carol. 2014. How many generations of pedigree data do you need? (pt 1). Institute of Canine Biology. https://www.icbblog.org/module-3/many-generations-pedigree-data-need-pt-1/

Beuchat, Carol. 2022. Do you know what you need to save your breed?  https://www.instituteofcaninebiology.org/blog/do-you-know-what-you-need-to-save-your-breed

Bowling, Sue Ann. 2010. Inbreeding coefficients for ROM Shetland Sheepdogs. https://bowlingsite.mcf.com/Genetics/Inbreeding2.html

Bowling, Sue Ann. Shetland Sheepdog ROM Inbreeding coefficients. https://bowlingsite.mcf.com/ROM/Inbreeding.html
​
Bowling, Sue Ann. Banchory Kennels and Sheltie History. https://bowlingsite.mcf.com/Banchory/Banchory.html

Bowling, Sue Ann. Key Imported Shetland Sheepdogs. https://bowlingsite.mcf.com/Imports/Imports.html

Dreger, Dayna ym. 2016. Whole genome sequence, SNP chips and pedigree structure: building demographic profiles in domestic dog breeds to optimize genetic trait mapping. Dis Model Mech (2016) 9 (12): 1445–1460. https://journals.biologists.com/dmm/article/9/12/1445/4004/Whole-genome-sequence-SNP-chips-and-pedigree

Ma, Justin. 2017. Can inbreeding be reversed? https://www.quora.com/Can-inbreeding-be-reversed/answer/Justin-Ma

Shetlanninlammaskoirat ry. 2022. Jalostuksen tavoiteohjelma vuosille 2023–2027. https://www.shetlanninlammaskoirat.fi/wp-content/uploads/2022/03/Shetlanninlammaskoirien-jalostuksen-tavoiteohjelma-2023%E2%80%932027.pdf

Suomen Ajokoirajärjestö. 2020. Suomenajokoirien käyttöominaisuuksien päivitetyt BLUP-indeksit on julkaistu 28.7.2020! https://www.ajokoirajarjesto.fi/6415/

Suomen Kennelliitto. KoiraNet Jalostustietojärjestelmä. https://jalostus.kennelliitto.fi/

Suomen Kennelliitto. Sukusiitos. https://www.kennelliitto.fi/kasvatus-ja-terveys/koiran-jalostus/tietoa-jalostuksen-tueksi/sukusiitos

The Kennel Club. Inbreeding calculators (COIs). https://www.thekennelclub.org.uk/health-and-dog-care/health/getting-started-with-health-testing-and-screening/inbreeding-calculators/