Frozen semen results vary among stallions. Some stallions have excellent semen quality after freezing while others have very poor results. Different freezing extenders and freezing methods can influence the quality of the frozen semen. The first step in the process is to perform a test freeze. Semen is collected from the stallion and analyzed for volume, concentration, motility, and morphology. If the semen quality is adequate, the freezing process begins. Several different freezing extenders and methods are used to determine which extender/method will result in better semen quality after thawing. The semen is diluted with a milk base extender and centrifuged. Centrifuging the semen separates the sperm from the remainder of the ejaculate. The supernatant is removed and discarded. The pellet containing the sperm is diluted with several different types of freezing extenders. The solution containing the sperm is packed in straws. At least two different freezing techniques are tested. First, the semen is frozen in the nitrogen vapor and then immersed in liquid nitrogen. The straws are placed in large nitrogen tanks and stored until they are used. One straw from each different freezing extender and method is thawed and the motility analyzed and compared. If results are favorable, then further semen collections are performed. If results are unfavorable, then the freezing technique is adjusted and the semen re-tested. Some stallions will just not freeze well regardless of the technique and their semen, should in these, cases not be used frozen. Several insemination doses or straws are obtained per semen collection. An average collection can yield 10 to 15 doses of frozen semen, but it can vary from 2 to 18 doses.