General points
Ideally, the criteria used during a BSE should reflect the subsequent proposed
use of the animal in question. Clearly, the requirements for a stallion expected
to impregnate 15 mares a year via AI with fresh semen on location will be
different to those for a stallion expected to impregnate the majority of 500
mares per year at distant locations. In the case of potentially popular stallions,
obtaining an accurate idea of sperm production capacity, ideally by measuring
daily sperm output (DSO), can be very useful in deciding a realistic number of
AI doses that can be produced per day (grossly exceeding this number may
lead to poor apparent fertility, despite there being nothing intrinsically wrong
with the stallion).
In many cases, AI stallions are required to combine their breeding duties with
a career as a sport-horse; the combination of predictable absences for
competitions, and unpredictable temporary falls in libido or semen quality as a
result of stress or exertion, may be a reason to establish a store of frozen
sperm, or to only offer frozen semen and thereby avoid the risk of having to
disappoint mare owners at short notice. The export market is also an
important reason to want to cryopreserve stallion semen. If frozen semen is to
be sold, however, i