Genetic Disorders Policy
Research indicates that genetic mutations, including those that cause disorders, occur in nature and more of these will be identified in the future as technology advances. It is important to understand that carrier animals of genetic disorders often have other genetic attributes desired by the industry. With genomic tools, management of deleterious alleles is possible to avoid undesirable disorders and reduce the allele frequency in the population over time while optimizing genetic progress. Therefore, efforts to eradicate or eliminate animals based on being a carrier of genetic disorders are generally not recommended, except in rare situations where their presence will result in substantial damage to the organization's viability.
BIF recommends the following strategic approach to diagnose, set policy, and manage genetic disorders.
Determining If a Genetic Disorder Exists
Protocol to determine if a disorder has an underlying genetic cause:
- Take pictures and/or video of the affected animal
- Collect tissues (i.e., tissue, whole blood) of the affected animal. Preserving the whole body of the affected animal is recommended.
- Capture DNA samples on the sire and dam of the affected animal.
- Have a veterinarian evaluate the affected animal and prepare a written report of their observations
- Provide as much pedigree and breed composition information as possible
- Work with the breed organization, genetics provider and/or university personnel to determine the appropriate entity to further analyze the situation.
Policies for Reporting and Testing Genetic Disorders
Once a genetic disorder has been identified, it is recommended that a pro-active approach for reporting and testing be taken. All breed associations should identify tested genetic carriers and potential carriers (identified by pedigree) on their registration certificate, the organization herdbook, and website. Test as many potential carriers as is economically feasible starting with the most widely used animals in that population (e.g., AI sires, donor dams). From an individual herd perspective, breeders should test sires to determine which, if any, active females need to be tested. This can be facilitated by collecting and storing tissue samples of previously used sires.
Animals that are carriers of known genetic disorders should be recorded, even in the rare situation where the organization chooses to eliminate carriers for breed viability. Organizations that are not practicing Whole Herd Reporting should develop a special recording category (with reduced or no fees) for these eliminated animals so that essential data are captured.
Breeding Management for Genetic Disorders
Once carrier animals have been identified then the disorder can be managed through both tactical and strategic approaches as part of the breeding program:
- The simplest strategy is to avoid mating potential carriers of the disorder to potential carriers of that same genetic disorder. However, care must be taken to identify what effect this approach will have on overall genetic improvement given that this strategy may unnecessarily sacrifice genetic improvement at the expense of avoidance of generating affected animals. For example, if a carrier bull's genetic merit is high and the allele frequency of the defect is low, the chance of generating afflicted offspring may not outweigh the value of the genetic improvement obtained.
- A more comprehensive approach would incorporate a mate selection framework. Mate selection is the simultaneous choice of selection candidates and their pattern of mate allocation, i.e., a mating list. Mate selection applications can manage genetic defects while simultaneously controlling for changes in inbreeding and genetic improvement of the breeding program.
A deeper dive can be found at https://beef-cattle.extension.org/managing-genetic-defects/
genetic conditions, genetic disorders, genetic defects, genetic variants
This article was derived from a report by a BIF ad hoc committee and further developed by several authors including User:Dbullock, User:Mspangler, User:Bgolden, and User:Snewman. Additional input was provided by the BIF Guidelines Committee.
- Ciepłoch, A., Rutkowska, K., Oprządek, J. et al. Genetic disorders in beef cattle: a review. Genes Genom 39, 461–471 (2017). https://doi.org/10.1007/s13258-017-0525-8
- Kinghorn, B.P. 2011. An algorithm for efficient constrained mate selection. Genetics Selection Evolution. 43:4.