Health Testing, Responsible Breeders, and the Stake Holders BY DR. CARMEN L. BATTAGLIA I n the world of purpose-bred dogs, history shows that there have been many healthy forms of breed improve- ment. Many were based on a series of little experi- ments. Some failed, but others succeeded and were
produce the traits that make each individual unique. What was also discovered was that it was not just the number of genes that were important, but also their efficiency, gene expression and the diversity of their proteins. For example, a single strand of tightly wound DNA is three microns long and fits into a space of only two-three cubic microns of a cell’s nucleus (roughly one millionth of a yard). With these discoveries, the question for breeders is not whether to use DNA tests or other protocols, but what to do with the results. In the past, many breeds suffered because quality dogs were thrown away, along with years of good breeding, because breeders did not know how to interpret and use test results. Today we know that when breed health initiatives are used they can become a demanding process that offers rewards for improved health for a breed or the misuse by uninformed breeders and their clubs. These events often lead to unin- tended consequences. Perhaps the better question is: can the undesired trait be inherited? Does it occur with increased frequency in your breed? What is the mode of inheritance? What is the reliability of the health test? If a health test or other protocol produces false-positive or false-negative results, breeders need to be careful because all of the descendants that inherit this portion of the chromo- some will also have false test results (Bell). This has been documented with families of Bedlington Terriers tested for the autosomal recessive copper toxicities gene (Bell). It is obvious that direct gene tests are better than linkage-based tests and a test with 90 % or 95 % level of confidence is better than no test at all (Bell). However, as genomic research pro- gresses, researchers will continue to identify the defective genes responsible for the disorders and they will also develop direct gene tests to replace linkage-based tests. For example, the defective gene for copper toxicities in the Bedlington Ter- rier has now been identified and a direct gene test is now pos- sible. But just having a test is not the solution. Unless breeders learn how to interpret and use the test results, progress will be slow and at a great cost. Because the majority of genetic disorders are caused by recessives, it is important to identify the affected, the carri- ers and the normal in order to find the solutions needed for making a breed improvement. To do this, breed clubs need to promote breeder education programs and provide mentors for new puppy buyers. Making a breed improvement and con- trolling unwanted disorders involves those who have learned how to manage the carriers. Good breeding also involves knowing how to use “Formula Breeding” and the principles of “Breeding Up” (Battaglia). No one approach is recommend- ed for every breed and every unwanted disorder. Pedigree analysis must be considered when using DNA tests, X-rays and other health protocols. For example, in a three generation pedigree there are 14 ancestors. Knowing only about a few ancestors can mislead breeders into believ- ing what is not true. What also becomes a factor is that breed- ers and owners who use health tests usually have some level of emotional reaction when a pup is produced with a genetic disorder. According to Dr. Bell, the reaction tends to follow what he calls a grief cycle: • Denial: This isn’t genetic. It was caused by something else. • Anger: This isn’t right! Why is this happening?
copied. Success varied widely from breed to breed and most were based, in part, on the creativity and imagination of the breeders. Now with the advances in research, a growing number of breeders have become more engaged in genetic “experiments” which occur each time they plan and carry out a mating. Some will use outcross mating which brings together two animals less related than the average for the breed. Breeding unrelated dogs tends to promote more het- erozygosity and usually more variation in the traits seen in their litters. A reason to outcross would be to bring in new genes or traits that are not present but needed. Outcrossing can also mask the expression of recessive genes and allow their propagation in the carrier state. Others will choose to line-breed which is an attempt to concentrate the genes of one or more specific ancestors through their appearance in the pedigree. Those who line-breed should use quality ancestors on both the sire and dam’s side of the pedigree and through careful selection choose offspring that meet the quality expected. Line breeding helps breeders make system- atic improvements with each breeding. Research has continued to be an important part of breed development and the combined funding by the AKC Canine Health Foundation and Morris Animal Foundation ($95 mil- lion), Nestle Purina Pet Care ($14 million) and Zoetis ($1.9 million), when taken together, have helped breeders pro- duce many notable accomplishments and a large number of healthy offspring. In 2003 the human genome project was completed with baffling results that found it was not just the number of genes that mattered but something else. For example, rice was found to contain 12 pairs of chromosomes, humans 23 and canines 39. Inside the chromosomes are the genes that “BREEDING UNRELATED DOGS TENDS TO PROMOTE MORE HETEROZYGOSITY AND USUALLY MORE VARIATION IN THE TRAITS SEEN IN THEIR LITTERS.”
170 • S how S ight M agazine , S eptember 2018
Powered by FlippingBook