Philippine Dog Finder

Remember that it is difficult to spot unaffected carriers. When an affected dog shows up, its pedigree is often examined for likely carriers. For example, PRA is a common problem in many breeds. There are dogs that come down with PRA that have a certain ancestor in common. That ancestor may then be considered a possible carrier and line breeding on him is avoided. This is a simplistic picture, obviously, since it’s possible for an unaffected non-carrier of PRA to come from an unaffected carrier that came from an affected dog (therefore the affected dog is in the unaffected dog’s pedigree). If a general blood test is ever developed that shows the presence of the recessive in an unaffected dog, then much more accurate breedings may be done; currently this is only possible for Irish Setters.

There is rarely only a single problem a breeder is trying to screen for. Suppose a suspected carrier of PRA is known for producing excellent hips. A breeder might therefore introduce that bloodline into theirs for the hips, and be willing to have the possibility of PRA show up in the line. In screening out one problem you might have to accept the possibility of another appearing.

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Inbreeding is where the sire and the dam are closely related: mother to son, father to daughter, sister to brother, half sister to half brother, cousin to cousin. People disagree about the exact point at which inbreeding becomes linebreeding. Inbreeding is the quickest way to find out what poor genes are in the line and what dominant characteristics are in the line.

Although many people are disgusted with the idea of this family incest, it is an extremely useful tool for diagnosing what genes are present. If the genes for bad eyes are present, but hidden or ressessive, this will bring them out to their full extent. If there isn’t any bad genes, then the puppies will be of very close uniformity and very able to reproduce themselves (theroretically). This is a homozygous breeding. The resulting puppies will have a lot of genetic material that is the same as their parents and grandparents and will be close genetically to each other.

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Line breeding is when the sire and the dam are distantly related: e.g., grandsire to granddaughter, granddam to grandson, second cousins, half cousins, uncle to niece, aunt to nephew….. The general strategy is that there is a common ancestor that is being doubled up on both sides. So the desired dog appears several times in the pedigree.

This is probably the most common strategy in breeding purebred dogs (and in developing new breeds, for that matter). Though this method, new genes are slowly introduced and unwanted genes are slowly replaced. The actual rate varies by how strongly you line breed. It sacrifices little overall quality in terms of show quality. Usually the puppies are rather close in general conformation. The only problem with this method is that it often takes several generations to get poor genes out, (or adding desired genes in) resulting in many puppies that have the same genetic problems (or virtues) that their parents have. And then because some breeders are more interested in winning, they do not place the affected puppies on spay/neuter contracts. This is both a blessing and a curse for the breed. If the breeder is very careful, affected pups can be used wisely to prevent loss of quality, but still remove the affected genes by only breeding the affected pups to known non-carrier relatives. This way the breeder can again try to “edit out” the bad genes. It takes longer this way but less show quality is lost in the process. This process results in dogs that will often reproduce their same level of quality. This is referred to as reaching homozygous litters (more genes of the same kind apparent in the puppies).

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Outcrossing is where the sire and dam are totally unrelated, preferably for three or four generations. The true form of an outcross is between two entirely different breeds because in reality the members of most registered breeds come from a common ancestor (althought it may be many, many generations back). It is very rare for outcrossed puppies to be uniform in appearance. Usually there are a very large ranges of sizes, coats, colors, markings, and other distinctive characteristics. Outcrossed litters are generally heterozygous, and do not reliably reproduce themselves, so even the nicest puppy in the litter may not later produce the best puppies.

Outcrossing is generally used to introduce something new to a line — a better head, better colors, better front, etc. Usually the puppies retained from these breedings are bred back into the breeder’s original line to standardize them back into the line’s general characteristics and reproducibility — with the one desired characteristic. The tricky part is that other characteristics may come along for the ride!

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If a purebred dog of breed X mated with a purebred dog of breed Y, both meeting health standards for their breed, is there a better chance the offspring would be healthier than a same breed mating because the gene pool is larger?

In terms of health alone the first answer would be that in breeding two healthy dogs it shouldn’t matter if they’re the same of different breeds, you’re apt to get healthy pups. But this doesn’t take into account the question of recessives. Suppose you breed two dogs of different breeds that both have the same incidence of a recessive health problem. The pups would have the same odds of having that health problem as purebred pups of either breed. On the other hand, suppose the two dogs were of breeds that have no recessive health problems in common. This would reduce or eliminate the odds of the puppies of having the health problems of either breed. This is the classic explanation for the theory of first generation hybrid vigor. The resulting pups should not be bred though, since they’d have a good chance of having the recessives from BOTH breeds, so the grandpups would be inclined to be worse off than the purebred offspring of their grandparents. An excellent set of articles dealing with “hybrid vigor” can be found in DogWorld, Jan 1997 by George Padgett DVM. Another very important point to keep in mind is that when a purebred carrying a genetic defect is crossed with another breed or mixed breed, the “bad” genes do NOT “go away” even though they may not be expressed in the offspring. If crossed with another dog carrying the same defect, the offspring of that breeding will demonstrate the defect.

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