However, if the quality of the raw ejaculate is an important factor in determining the post-thaw quality, it would seem quite obvious that no stallion should be collected for freezing while he is sexually rested. Collection of at least two or three ejaculates prior to the first freezing should be done to maximize the quality of the raw semen. This procedure should be done even when the semen looks good under the microscope. For every step in the process, there are a number of alternatives that can be used. Recent investigations have revealed that freezing semen also affects several other parameters involved in the fertilization process.
Fewer sperm reach the site of fertilization or perhaps take a longer time to reach it.
Furthermore, sperm cells that are frozen and thawed have changes in their level of calcium, which is an important factor during the time that sperm cells need to prepare for fertilization. All of these changes that happen to sperm during the freezing and thawing process affect the ability of the mare to form a sperm reservoir that would otherwise normally happen when mares are bred by natural cover or with fresh semen. However, this involves more labor for both veterinarians and mare owners. Although it has been suggested that differences in the composition of the extender will improve the post-thaw motility of certain stallions, recent experimental data have not supported this concept. However, it is well accepted that the raw semen from stallions which are considered good freezers have lower volumes, higher sperm concentrations, and higher sperm motility compared to the semen from the those classified as poor freezers.