Gene defect - Mutation 

A gene defect is the deviation of a certain genetic information that leads to a defective gene product.
The defective gene product subsequently leads to symptoms of malfunction, which can vary in severity depending on the type of defect and the importance of the affected gene.

Gene defects that lead to early death in the embryonic phase (embryonic premature death) remain unnoticed and can be one of the reasons for the absence of pregnancies.

Gene defects can be acquired or inherited.

In the case of inherited defects, the affected animal has the defect from its parents; acquired genetic defects result from damage to the genetic material in the animal itself by external and internal impacts (radiation, poisons).

In some defects, the phenotype of an acquired defect cannot be distinguished from that caused by a gene defect.
If it is not clear whether the cause is a gene defect or whether the defect has arisen as a result of trauma or disease, this usually leads to exclusion from breeding.
The purpose of exclusion is to prevent the introduction of as yet unidentified and/or newly developed genetic defects into the breeding population.