Knowing how defective genes propagate into the next generation helps us make management decisions that allow for the use of carrier animals. Of course, no one system fits all operations or all defects. Points to think about when deciding how to manage against defects include the economic impact of the condition, the frequency of the broken gene within the herd, the availability and cost of DNA tests, the genetic merit of the carrier animals, and whether you raise seedstock or commercial cattle. Some strategies to consider when using known defect carrier breeding stock in either commercial or seedstock operations are as follows:
● Use crossbreeding to greatly reduce the risk of carrier to carrier matings (and boost production by up to 25%)
● If crossbreeding is not an option, then use outcrossing to avoid inbreeding and the concentration of particular defective genes
● Carrier to non-carrier matings can be used in terminal production systems without the risk of increasing the frequency of the defective allele in the breeding herd as none of the offspring will be maintained and carrier to non-carrier matings should not have any affected animals if the trait is recessive (offspring need to inherit two copies to show the phenotype).
● Test for known defects in your influential breeding stock (sires and donor dams) to identify at risk bloodlines
● Archive DNA of influential breeding stock (semen or hair) for yet unavailable DNA tests
● If a carrier animal is of high-genetic value, mate the carrier to non-carriers and test the progeny for carrier status (50% of the progeny should be free).