DNA testing for genetic diseases are a great opportunity for breeders to avoid disease affected dogs and improve the breed. However, geneticist usually strongly advise against rushing into restricting breeding to only animals completely free of disease as it can result in a loss of genetic variability, loss of valuable selected traits and the emergence of other genetic problems. The continued use of carriers in breeding programs and testing of offspring for inclusion in breeding for the next generation is recommended to avoid this problems.
Phasing in of breeding restrictions over a period of time is one way to enforce testing and eradication of the diseases. Border Collie breeders face a problem with 3 different genetic disorders that are very common and have tests available. The diseases are fatal nerve disorder, CL, the potentially fatal immune disorder, TNS, and the eye disorder CEA.
The effect of rushing into restricting breeding could be to dramatically reduce the gene pool and force other genetic problems such as epileptic fit, glaucoma, monorchidism to become more prevalent. Then when tests are available for these the cycle will repeat itself. How long breeders need to be able to preserve all the desired traits of the breed while slowly breeding out the genetic defects is for the breeders to discuss and reach agreement.