When considering a pair for breeding, breeders must take into account numerous factors that affect the overall outcome before deciding on which pair to breed. It is a breeder's responsibility to consider such things as working instinct, conformation, temperaments and pedigrees. But equally or even more importantly the breeder must also consider the genetic soundness of each, the sire and dam.

Through regular CERF, BAER, OFA and other tests breeder's can determine which terriers are affected. Until genetic markers for these diseases are identified, we cannot determine the carriers. And until we can determine carriers, carrier-to-carrier matings will undoubtedly occur, producing yet more affected and carrier offspring.

Below is a graphical representation of what we know about how genetic defects are inherited through breeding.

Clear-to-Clear

Breedings Produce

100% Clear

Clear-to-Carrier

Breedings Produce

50% Carriers

50% Clear

Clear-to-Affected

Breedings Produce

100% Carriers

Carrier-to-Carrier

Breedings Produce

50% Carriers

25% Clear

25% Affected

Carrier-to-Affected

Breedings Produce

50% Carriers

50% Affected

Affected-to-Affected

Breedings Produce

100% Affected

Currently the only means of detecting carriers is through "Test Matings" (breeding to a known carrier or affected terrier) or unintentionally, by breeding a pair and that breeding resulting in producing affected offspring.

Test Matings:

Since currently we have no tests available to determine carriers, some breeders have used the controversial yet effective method of performing "Test Matings" to determine carriers of particular diseases. If there is question as to whether or not a particular terrier is a carrier of a genetic defect, this can be determined through "Test Matings" with a known affected terrier. If there are no "affected" puppies produced, chances are the terrier in question is "clear". If 50% of the litter is "affected", then the terrier in question is at least a "carrier". If 100% of the litter is "affected" then both the sire and dam are "affected".

It is very important though that breeders taking part in these types of "Test Matings" keep in mind that because the litter was produced with a known affected terrier, even if no affected terriers were produced, the entire litter, 100% are carriers. And if these offspring are to be sold, the breeder has a responsibility to inform the buyer/s that the puppy/s are carriers. And in the case where affected terriers were produced, determining that the terrier in question is at least a carrier, the other 50% of the litter are carriers. Note; a breeder taking part in this type of "Test Matings" should be prepared in any case to keep track of this litter produced for years to come, to determine "late onsets" of some diseases and any other changes that might occur.

Even though "test matings" are controversial it is yet effective in determining carriers of genetic defects. But with your donation and support the JRTRF can be just as effective in determining carriers of diseases. The JRTRF is committed and dedicated to working towards the day when carriers of genetic diseases can be identified, and unintentional carrier-to-carrier matings will no longer threaten our beloved breed.

For the Jack Russell Terrier Research Foundation to be an effective tool, the JRTRF depends upon donations, support and information. With these donation the JRTRF can fund research projects. And with your cooperation in providing information through surveys, the JRTRF can provide Researcher’s with valuable information needed many times to proceed.

From The Book "Future Dog, Breeding For Genetic Soundness"

Every breeder is a keeper of the "genetic flame" for his or her breed. Every breeding decision an individual breeder makes has the potential to affect the future of the breed. For conscientious breeders, each attempt to produce quality purebred dogs includes a strong commitment to reduce inherited disease. Line-breeding, the tool largely responsible for creating the variety of dog breeds we are familiar with today, inadvertently also aggregates deleterious genes, producing disorders that may not be apparent in every generation.

These disorders often go undetected until the condition becomes frequent enough to be recognized as inherited. Generations may be unaffected when carriers are rare. As unaffected carriers become common, more affected individuals will appear. Removing affected individuals from the breeding population is not an effective solution since many unidentified carriers remain. The disease-producing genes will continue to spread unless unaffected carriers can be identified and selective breeding practiced.

Author: Patrick J. Wilkie

Published by the Minnesota Agricultural Experiment Station in cooperation with

the AKC Canine Health Foundation. Canine Health Foundation