Breeders vs canine biologist +kennel clubs. There are '4' different breeding strategies: 1)inbreeding 2)Linebreeding 3)Like for like(best to best) 4)Outcross (hybrid breeding) It is proven fact that closebreeding especially when COI reaches 25% deleterious effect MAY start cropping up. Firstly ,it's good to note almost all living things have two alleles: dominant & recessive. Secondly,recessive alleles are loaded with junks -all sorts of health ish. So it's safe to say all living things have hidden deleterious genes in its recessive gene. However,our dominant gene masks/overrides /covers these faults. These hidden faults become dominant as a result of pairing of two recessive genes basically due to inbreeding- so when these two hidden faults find each other as a result of inbreeding the effect becomes prominent. "This is just a vague explanation." Due to so many breeds plagued with deleterious faults, laws have been enacted by kennel clubs to ensure within 5generation COI is kept at a level below 10% EXCEPT IN RARE CASES. These laws did not and still don't sit well with working dog breeders cos they believe to retain desired traits (set type for form and function) and for gene stability (for predictability in character) inbreeding and linebreeding is basically the only strategies they believe can be used to lock in desired traits both for phenotype and genotype. Breeders are consumed with uniformity ,biologist are consumed with biology fitness(health vigour) . While breeders believe they will cull the weak(both form and function) and breed only the STRONG. Biologist are of the opinion ,EVERY DOG IN A LITTER CAN CONTRIBUTE TO THE GENEPOOL WITHOUT THE NEED OF CULLING IF COI IS BROUGHT TO THE LOWEST. Biologist won the war as they've proven to government & kennel clubs that closebreeding hurt dogs population with several health issues from cancer to hip dyplsia to epilepsy etc. This gave birth to government & kennel clubs setting new breeding standards so as to reduce and manage breeds genetics. I.e in Holland ,finland sweden and many more no inbreeding or linebreed COI of 6% and above . And in 5generations the inbreeding(coi) shouldnt be up to 10% Led by FCI. Due to this, breeders are limited to Best to Best and distance relative breeding i.e 2nd cousin,3rd couisn etc. However some breeders due to these laws stopped registering their dogs with clubs cos they felt this will reduce the workability and hardness of their dogs. Breeds Firstly ,it should be noted COI of 25% is a breaking point that should bringforth deleterious faults or at this same level ceil a trait. Secondly ,how can COI of 25% be reached ASAP? A)father/daughter or mother/son breeding =25% B)brother/sister =25% Also linebreeding can get to COI of 25% but not as fast as inbreeding. Meaning linebreeding can equally become inbreeding at : A)Two generation of breeding half brother to half sister =25% B)Three generation of linebreeding Double first cousin=25% .etc. NB: The more backward an ancestor appears in a pedigree,the lesser his/her contribution. This is why linebreeding is used to intensify such ancestor's contribution. What's the fuss with biologist? Atleast GSD was created by intense inbreeding and linebreeding, the DDR was bred for 41 years of close family breeding which some still guard jealously till today. Colby bloodline which is the offshoot of almost all "strains of pitbulls" was closely bred for over 100years with only one single outcross yet this line is still regarded. Though some breeds can't tolerate certain levels of inbreeding i.e dogo argentino ,bull terrier ,american bulldogs british bulldogs ,Dalmatians, Rottweiler etc.This is not to say others can, though some have better degrees i.e APBT and "horses"(breeding thoroughbred race horses). The German Shepherd Dog pedigree... A Data from Dreger et al 2016 (From the blog post Inbreeding of purebred dogs determined from DNA) includes the GSD to at 27th highly inbred dog by SNP. Standing on the chart at over 25%. Because of some genetic anomalies, the GSD like some other breeds under FCI states more than 7% of aggregate COI is getting too intense. But of course we must understand that some matings with 0% COI still bring out anomalies like HD, fertility issues, testicle descending issues, etc. This is why some breeders still use Estimated Breeding Value(EBV), experiences about a particular family,& other tools as guide before embarking on a pairing. Or you hear discussions like Grim z PS and Fero lines work fine. Zamp Thermodos and Ballack lines work fine etc(these logics are based on experience and consanguinity). But hell! Breeding can still be a crap shoot, therefore best way is to ensure BEST PRATICES to remove all possible doubts.