Analysis of stallion semen and its relation to fertility.

This article describes some of the basic methodology for conducting stallion semen evaluations. Not all of these assays will likely be conducted on every semen sample collected. Routine evaluations should include determination of semen volume, sperm concentration, and an estimation of the percentage of progressively motile sperm, at a minimum. Other assays can be used if a seminal problem is discerned at the beginning of the breeding season or after a stallion has recovered from an illness or injury. Additionally, laboratory assays are particularly important to conduct on cryopreserved spermatozoa, because these cells have been exposed to substantial temperature and osmotic insults (see Cryopreservation of Stallion Spermatozoa, this issue). The percentage of fully functional sperm is reduced during cryopreservation and the longevity of the cells surviving freezing is shortened. Therefore, to maintain high fertilization rates using cryopreserved sperm, only sperm samples containing sufficient numbers of high-quality cells should be used. Unfortunately, no single laboratory assay can estimate the fertilizing potential of a semen sample. What these analyses can do is discern semen samples that are likely to have poor fertilizing capacity.