Dog Breeding – Maintaining Good GeneticsGenetics is the study of how traits are inherited. Genotype is the genes that are carried, while the phenotype is what we see in the dog. We manipulate these traits to get different dog breeds or colors. Genetics is also how we breed away from detrimental issues like hip, hernias and eyes. But how does this all work?
Co-dominance or incomplete dominance is the merle gene in dogs. Heterozygous Mm desired merle color, while MM merle shows mostly white and often is blind, deaf or worse. The mm phenotype is normal color.
Line Breeding Vs. InbreedingLine breeding is the breeding of ancestors behind both parents. Line breeding concentrates the genes of specific common ancestors or sets traits such as color, coat or size. Inbreeding is the mating of close relatives such as parent x offspring, sister x brother. The public finds this unacceptable, and it is not recommended. Line breeding and inbreeding increases homozygosis (aa or AA) in offspring.
Genetic disorders or traits can be caused by a single gene pair (monogenetic) or several pairs of genes (complex or polygenetic). We are most interested in polygenetic traits with variable expression. Hernias, hip issues and Progressive Retinal Atrophy (PRA) are examples of polygenetic inherited traits.
Polygenetic TraitsA number of liability genes must combine to cross a threshold and produce the affected individual. Both sire and dam carry a genetic load of liability genes. Polygenetic issues are difficult to select for or away from. A firm veterinary diagnosis must be established so we know what the issue is and that the diagnosis is accurate. Search widely in the pedigree to see if this condition exists with increased frequency in your line. Even if we do not know the inheritance, we can select away from the issue.
Maintain the Line and the Good GenesOur goal is always to maintain the line and produce fewer "bad genes" in each new generation than in the last. By selecting less affected offspring and replacing more affected parents, we remove the gene phenotype and genotype.
Maintaining your line is the goal, as well as eliminating phenotype issues. Your next sire family must have less liability genes than the average for your breed. With traits that are multi-gene inherited, finding a sire with no PRA or Hip Dysplasia genes is not possible. If you are seeing the trait, you have it in both the sire and dam and enough of these genes are coming together to cause the issue or phenotype in the puppy. The genes came from both sides and therefore a "common ancestor" concentrates the genes they contributed and likely the problem genes. Search the pedigree for a common ancestor that gave multiple genes to both sides of the pedigree, in order to avoid that line and guide you in your next sire selection.
In the past, we eliminated a line or tried not to breed the affected line but that was wrong as we eliminated good genes. Maintaining genetic diversity of your population is essential for progress. If you just outbreed without working to eliminate the genotype, you will fail. You will deal with it again in future generations because what you did was just disseminate detrimental recessive genes through your line. Each generation must have fewer liability genes than the last!
If You Cannot Select from a Defect-Free LitterBe sure you know the genetic defect and how to diagnose. Select a normal female who is free from phenotype (i.e. hernias or hips). Breed this female to a male who is from sibling-free breeding. Replace the higher risk female with quality, lower risk offspring and repeat the process. Each generation will have a lower frequency of liability genes yet maintain the desirable genetics of the line. You decrease the risk, and the phenotype will not show up in future generations.
Environment plays a role but defects will only show up if you have the genes for it. Poor nutrition can alter expression of musculoskeletal disorders such as hip, Hypertrophic Osteodystrophy (HOD), Legg Perthes and knees, especially in the growth phase. Environment can not cause issues if the puppy is not prone to the phenotype. It is so important to decrease the liability genes in your line!
Get a Direction
- Welcome feedback from your clients on issues they are seeing.
- Request a veterinary letter so you know how they diagnosed the condition and that it is accurate.
- Get a game plan that includes genetic testing in breeding stock. Testing is once in a lifetime!
- Work with people in the breed that know the condition and eliminate it.
Genetics do not tell you what you will see. Genetics tell you what you might see. Improved genetics is not a sprint, it's a marathon. A consistent plan is always a winner!
If you need help, call us at 800.786.4751.
Don Bramlage, DVM, Former Director of Veterinary Services at Revival Animal Health
The materials, information and answers provided through this website are not intended to replace the medical advice or services of your personal veterinarian or other pet health care professional. Consult your own veterinarian for answers to specific medical questions, including diagnosis, treatment, therapy or medical attention.