provided by regularly repeated semen collection. In this respect, the 2
ejaculates collected approximately one hour apart during a standard BSE are
rarely sufficient to really indicate sperm production capacity or baseline semen
quality (the number and quality of sperm in the second ejaculate is only a very
rough indication of the baseline). Instead, it is preferable to collect semen
daily for 5-7 days, until the stallion reaches daily sperm output (DSO:
Thompson et al., 2004). Thereafter, total sperm numbers and, more
importantly, total numbers of progressively motile, morphologically normal
sperm (x 106: TNM) can be calculated using standard semen quality
parameters, i.e. gel-free volume, concentration, percentage of (progressively)
motile sperm, and percentage of morphologically normal sperm (Colenbrander
et al. 1992). The daily TNM can be used to estimate the number of AI doses
that can be produced per day. In the Netherlands, a normal AI dose is
expected to contain at least 300 TNM and, since sperm quality will deteriorate
during transport, it is standard practice to package 600 TNM when semen is
transported at 5-7oC. While the number of sperm per dose used for frozen
semen AI have reduced significantly with the advent of deep intra-uterine
insemination techniques, suggested minimums for a standard frozen semen
AI dose are 800 x 106 total sperm or 250 x 106 progressively motile sperm
(Sieme, 2009).
Additional tests that are useful when determining whether a stallion is
acceptable for inclusion in an AI programme depend on how the semen will
subsequently be stored and transported.
Semen to be transported at 5-7oC: If the semen is intended for chilled
transport of more than 6h duration, the longevity (i.e. preservation of viability
and progressive motility) during chilled storage should be tested. Ideally, initial
testing should include more than one extender (egg-yolk or skimmed milk
based; different antibiotics) and preparation method (dilution at a ratio of at
least 1:3 times with extender to a concentration of <50 x 106/ml; or
centrifugation to remove the bulk of the seminal plasma followed by resuspension at around 20 x 106/ml) to determine which give acceptable results;
there are significant between-stallion differences in ability to withstand the
presence of seminal plasma or to tolerate different extenders. The semen
should be gradually cooled (0.3 oC/minute) to 5-7oC in an appropriate storage
container, and the percentage of (progressively) motile sperm checked at
intervals over approximately 48 hours (e.g. 6, 12, 24 and 48h). Adequate
semen quality after 24-48h of storage (e.g. >35 % progressively motile sperm,
>35% morphologically normal), is taken as being consistent with the potential
for adequate fertility via cooled transported semen (Samper, 2009). Assessing
sperm quality after a period of storage, also gives an indication of anticipated
sperm loss rates during transport, and thereby allows more accurate
calculation of what should be an acceptable dose at the time of shipment.
Frozen-thawed semen: Frozen-thawed semen accounts for a steadily
growing proportion of sport-horse mares inseminated in, and of stallion semen
exported from, a number of European countries. While frozen-semen AI was
initially unpopular, it is now clear that pregnancy results can be perfectly
acceptable for many stallions, assuming adequate attention is paid to the
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February
2016
East
London
Convention
Centre,
East
London,
South
Africa
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