An important factor in ensuring high fertility rates in parent and grandparent stock is the quality of the semen. This is particulary true when breeders are housed in cages. In floor systems, male behaviour and anatomy are much more the limiting factors than semen quality. A male that is incapable of mating will not only have no offspring, but can also prevent other males from mating with a certain group of females.

There are many methods for evaluating semen quality. The easiest way is to observe its volume, colour, and consistency. For a more precise picture, microscopic evaluation can be used. The most valuable traits are:
- mobility,
- clumping of spermatozoa, and
- presence of morpholgically abnormal cells

Other more complicated methods, such as the fluorimetric technicque, are described in the literature. There is not often a need to use these complicated techniques when microscopic evaluation is available as it is an effective and relatively simple method.

Another method is to look not at the sperm cells, but at the number of holes in the blastoderm, that are caused by penetrating sperm cells. This is an indication for both the concentration, activity and liveability of the sperm cells that actually reach the egg cell for fertilization.

The development of spermatozoa takes several weeks, so especially in the case of abnormal cells the cause will be several weeks old also. This is important to realize, if causes for reduced vitalitiy are analysed.

The quality of semen can be influenced by many factors, including male condition, nutrition, toxins, storage time, dilution, etc. Recently is has been proven that for instance, organic selenium (selenium bound with methionine) is effective in increasing and maintaining semen quality.